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Academic Exchange

Time and place: 2020.10.29, 19:00 pm, Skype Meeting

Presenter: Gregory S. Nusinovich

Title: Remote detection of excess ionizing radiation by using focused powerful terahertz wave beams

Abstract:A high-power source of sub-THz radiation allows one to remotely focus this radiation in a small volume where the RF electric field will concealed radioactive materials as a new application of gyrotrons.In this lecture, I am planning to start by describing the concept of remote detection of excess ionizing radiation by using high-power gyrotrons and some experiments with the 200kW, 0.67 THz Gyrotron. Then, I will focus on the working conditions of remote detection: formation of the breakdown-prone volume, production of free electrons by gamma rays and minimum detectable mass. Next step will be atmospheric conditions on the propagation and focusing of THz wave beams. The last part of this lecture will be devoted to plasma formation.

                                                                                                                                                                                                                                           

Time and place: 2020.10.15, 9:30 am, VooV Meeting

Presenter: Hu Miao

Title: Photon-based Spectroscopy Studies of Quantum Materials

Abstract:Correlated quantum materials possess remarkable physical properties, such as high-Tc superconductivity, anomalous Hall effect, novel topological orders etc. Yet, the underlining physics of these emergent quantum phenomena remain poorly understood. In recent few years, benefited by the fast development of new generation of x-ray light sources, ultra-high resolution inelastic x-ray scattering, fully coherent x-ray beam with nanometer x-ray spot, femtosecond time-resolution x-ray free electron laser (xFEL) become available to directly study the emerging low-energy excitations and their ultrafast processes. In this talk, I will present our works on various quantum materials and show how spin, charge and lattice excitations interact with each other and how these excitations conspire to determine the macroscopic physical properties.

                                                                                                                                                                                                                                           

Time and place: 2020.10.8, 16:00 pm, VooV Meeting

Presenter: Xiangang Wan

Title: Calculated Exchange Interactions and Competing S=0 and S=1 States in Doped NdNiO2

Abstract:Using density functional based LDA+U method and linear-response theory, we study the magnetic exchange interactions of the superconductor Nd1-xSrxNiO2. Our calculated nearest-neighbor exchange constant J1=82 meV is large, weakly affected by doping and is only slightly smaller than that found in the sister compound CaCuO2. We however find that the hole doping significantly enhances the inter-layer exchange coupling as it affects the magnetic moment of the Ni-3d{3z2-r2} orbital. This can be understood in terms of small hybridization of Ni-3d{3z2-r2} within the NiO2 plane which results in a flat band near the Fermi level, and its large overlap along z direction. We also demonstrate that the Nd-5d states appearing at the Fermi level, do not affect the magnetic exchange interactions, and thus may not participate in the superconductivity of this compound. Whereas many previous works emphasize the importance of the Ni-3d{x2-y2} and Nd-5d orbitals, we instead propose that the material can be described by a Ni-3d{x2-y2}/Ni-3d{3z2-r2} two-band model. Its solution is studied here on the level of Dynamical Mean Field Theory and reveals an underlying Mott insulating state which, depending on precise values of the intra-atomic Hunds coupling, produces upon doping competing S=0 and S=1 two-hole states at low energies that lead to very different quasiparticle band structures. We propose that trends upon doping in spin excitational spectrum and quasiparticle density of state can be a way to probe Ni 3d8 configuration.

                                                                                                                                                                                                                                           

Time and place: 2020.9.17, 19:00 pm, Zoom Meeting

Presenter: Gregory S. Nusinovich

Title: Introduction to gyrotrons: principles and applications

Abstract:Gyrotrons are well known as high-power sources of coherent electromagnetic radiation. In the millimeter- and submillimeter-wavelength regions, the power that gyrotronscan radiate in continuous-wave and long-pulse regimes exceed the power of classical microwave tubes by many orders of magnitude. In this lecture, I will give an introduction to the history of the development of gyrotrons. I will start by describing three kinds of coherent electromagnetic radiation by electron beams: Cherenkov or Smith-Purcell radiation, transition radiation, and bremsstrahlung. Then, I will focus on bremsstrahlung, and move from that (describing the history of studies) to cyclotron resonance masers (CRMs). The next step will be the invention of gyrotrons. The last part of this lecture will be devoted to gyrotron applications.

                                                                                                                                                                                                                                            

Time and place: 2020.9.16, 9:00 am, VooV Meeting

Presenter: Jiaxin Yin

Title: Scanning tunneling microscopy of emergent topological matter

Abstract:The search for topological matter is evolving towards strongly interacting systems including topological magnets and superconductors, where novel effects and unusual phases emerge from the quantum level interplay between geometry, correlation, and topology. Equipped with unprecedented spatial resolution, electronic detection, and magnetic tunability, scanning tunneling microscopy has become an advanced tool to probe and discover the emergent topological matter. In this talk, I will review the proof-of-principle methodology to study the elusive quantum topology in this discipline, with particular attention on the studies under a vector magnetic field as the new direction, and project future perspectives in tunneling into other hitherto unknown topological matter.

                                                                                                                                                                                                                                            

Time and place: 2019.12.20, 13:30 pm, Wuhan National High Magnetic Field Center C204

Presenter: Jian Shi

Title: Phase Transitions of Correlated Oxides and Neuromorphic Electronics

Abstract:As the finest computing system in our planet, human brain outperforms IBM Blue Gene at many aspects (energy efficiency, memory capacity and computational speed). Inspired by biological neural systems, neuromorphic systems open up new computing paradigms to explore cognition, learning and limits of parallel computation. In our brains, synapse is believed to be responsible for the learning and memory behaviors. The success of synapse concept at software-level artificial neural networks in the applications of voice and image recognitions has been driving the search for their hardware counterpart – synaptic transistor. Here we emulate the synapse by using a strongly correlated oxide – SmNiO3

                                                                                                                                                                                                                                            

Time and place: 2019.11.22, 15:00 pm, Wuhan National High Magnetic Field Center B206

Presenter: Marc Janoschek

Title: Dissecting Metallic Quantum Matter with Neutrons

Abstract:When many quantum particles interact in a solid frequently unexpected collective behavior emerges that is extremely difficult to predict. A prime example are metals near magnetic quantum phase transitions, notably magnetic instabilities in the zero-temperature limit that are accessed by non-thermal tuning parameters such as pressures and magnetic fields, at which strong electronic correlations manifest via new energy scales, as well as the emergence of novel quantum matter states. Examples include charge stripe and loop order, electronic nematic order, “hidden” order, multipolar order, and unconventional superconductivity. The SINQ neutron source at PSI provides a unique toolset for high-precision studies of such quantum matter states with access to the underlying energy scales and the associated collective behavior. I will provide an overview of current frontiers and developments in the field. I will summarize the progress made by recent neutron scattering experiments carried out by us and others and discuss how they offer the potential for exciting break throughs in the understanding of metallic quantum matter, notably in the extreme of high magnetic fields.

                                                                                                                                                                                                                                             

Time and place: 2019.11.14, 14:30 pm, Wuhan National High Magnetic Field Center C204

Presenter: Zhi Wang

Title: Intrinsic hysteresis of topological Josephson junctions with Majorana zero modes

Abstract:Topological Josephson junctions are distinct from conventional ones in that they host Majorana bound states which form a two-level quantum system, the so-called Majorana qubit. The energies of the two levels are depending on the Josephson phase across the junction,while reversely the effective potential for the Josephson phase is controlled by the wave function of the Majorana qubit. We build a quantum resistively shunted junction model to describe the correlation between the Majorana qubit and the classical Josephson phase. Within this model, we study the I-V characteristics of the junction, and demonstrate an intrinsic hysteric behavior which is independent of the parameters of the junction. Our results are quantitatively in agreement with recent experiments.

                                                                                                                                                                                                                                               

Time and place: 2019.11.13, 15:00 pm, Wuhan National High Magnetic Field Center B206

Presenter: Ke He

Title: The road to high temperature quantum anomalous Hall effect in magnetic topological insulators

Abstract:The quantum anomalous Hall effect is a quantum Hall effect that can occur without applied magnetic field. The effect has been experimentally realized in magnetically doped topologically insulators, but usually an ultralow temperature below 100mK is required to observe full quantization of the anomalous Hall resistance and vanishing longitudinal resistance. Elevating the temperature to realize the quantum anomalous Hall effect to above 77K or higher is crucial for its practical applications in electronics. In this talk, I will review the progresses in the past years on searching for higher temperature quantum anomalous Hall systems. Based on our understandings on these results, especially recent ones on magnetically intercalated topological insulators, we will give the principles and a roadmap for designing and constructing materials to realize high temperature quantum anomalous Hall effect.

                                                                                                                                                                                                                                                

Time and place: 2019.11.4, 10:30 am, Wuhan National High Magnetic Field Center B206

Presenter: Xuerong Liu

Title: Delocalized local orbitals in iridates: dimerization and molecularization

Abstract:Besides the charge and spin degrees of freedom, in transition metal compounds the orbital degree of freedom could lead to nontrivial consequences. The relativistic spin-orbit coupling (SOC) promotes the significance of the orbital degree of freedom, and has led to the so called SOC assisted Mott insulator concept in the iridates. If the strong SOC is embedded into special crystal geometry, and consider equal footing competition from hopping, more interesting quantum objects, such as dimer and molecular orbitals, could be realized. Combined with resonant inelastic X-ray scattering (RIXS) measurements and theoretical calculation, we demonstrate the dimer states in Ba5Allr2O11.

                                                                                                                                                                                                                                                 

Time and place: 2019.9.23, 16:00 pm, Wuhan National High Magnetic Field Center C204

Presenter: Yong Xu

Title: Intrinsic magnetic topological insulator MnBi2Te4

Abstract:The interplay of magnetism and topology is a key research subject in condensed matter physics and material science, which offers great opportunities to explore emerging new physics, like the quantum anomalous Hall (QAH) effect, axion electrodynamics and Majorana fermions. However, these exotic physical effects have rarely been realized in experiment, due to the lacking of suitable working materials. In this talk, we will present our recent findings of intrinsic magnetic topological insulators in van der Waals layered MnBi2Te4-family materials. The materials intrinsically show two-dimensional (2D) ferromagnetism in the single layer and three-dimensional (3D) A-type antiferromagnetism in the bulk, which could serve as a next-generation material platform for the state-of-art research. We predict extremely rich topological quantum effects with outstanding features in an experimentally available material MnBi2Te4, including a 3D antiferromagnetic topological insulator with the long-sought topological axion states, the type-II magnetic Weyl semimetal (WSM) with one pair of Weyl points, and intrinsic QAH insulators and axion insulators. Recent theoretical and experimental progresses will be introduced. As important progresses, we experimentally observed two exotic topological phases (i.e., axion insulator and Chern insulator) and quantum phase transition between them in one stoichiometric crystal MnBi2Te4 at relatively high temperature.

                                                                                                                                                                                                                                                 

Time and place: 2019.9.16, 9:30 am, Wuhan National High Magnetic Field Center B206

Presenter: Youguang Guo

Title: Some Research Activities on Electric Motors and Drives at UTS CEMPE

Abstract:Electric motors and drive systems play a key role in modern industry and domestic applications. This talk aims to present some research activities and ideas at the Center for Electrical Machines and Power Electronics (CEMPE), University of Technology Sydney (UTS). The focus will be the advanced material application and system-level multi-discipline optimization, which are considered as the crucial issues for developing high-performance electric drive systems. The talk also tries to explain the significance, innovation and urgency of these topics.

                                                                                                                                                                                                                                                 

Time and place: 2019.7.4, 14:30 pm, Wuhan National High Magnetic Field Center B206

Presenter: Congjun Wu

Title: Orbital-active honeycomb materials

Abstract:We provide a unified view for a class of orbital-active honeycomb materials, including bis-muthene, stanene, exciton-polarition lattice, and the recent focus of the twisted bilayer graphene. These materials are orbital-active possessing a pair of degenerate px and py orbitals on each site, which are unified under the E-representation of the C6v group symmetry. We started the research on orbital-active honeycomb systems in ultra-cold atom optical lattices, and found that similar physics also applies to the above solid state materials unified under the same symmetry structure. For solid state applications, we propose a new mechanism to boost the topological gap to the full scale of the atomic spin-orbit coupling, i.e., the order of 1eV. This mechanism has been recently realized in experiments of bismuthene on SiC, which shows the evidence of the gap up to 0.67eV. Mech-anism for unconventional superconductivity assisted by the orbital structure in this class of mate-rials is also studied. The flat band structure arises in 2D orbital-active honeycomb materials, such as organic metal frameworks and transition metal oxide films, in which strong correlation phe-nomena including Wigner crystallization and ferromagnetism appear.

                                                                                                                                                                                                                                                 

Time and place: 2019.5.21, 9:30 am, Wuhan National High Magnetic Field Center C204

Presenter: Haifeng Li

Title: Neutron/synchrotron X-ray scattering studies of strongly-correlated electron systems

Abstract:The first question we pose while studying any new family of correlated electron materials is the question concerning the internal structure: what are the crystalline and magnetic building blocks and how are they arranged? The second question concerns the microscopic dynamics: how do these building blocks move and what are their internal degrees of freedom? These herculean tasks can be accomplished by modern neutron and synchrotron X-ray scattering. Especially, neutron scattering is a unique powerful tool to solve magnetic structures and determine magnetic excitations and fluctuations. In this talk, I will present our work on iron-based superconductors & intermetallic compounds, focusing on the studies of crystalline and magnetic structures as well as spin dynamics, investigated mainly by neutron scattering technique.

                                                                                                                                                                                                                                                 

Time and place: 2019.5.17, 10:00 am, Wuhan National High Magnetic Field Center B206

Presenter: Yi Zhou

Title: Hidden SU(2) Symmetries, the Symmetry Hierarchy and the Emergent Eight-Fold Way in Spin-1 Quantum Magnets

Abstract:The largest allowed symmetry in a spin-1 quantum system is an SU(3) symmetry rather than the SO(3) spin rotation. We reveal some SU(2) symmetries as subgroups of SU(3) that, to the best of our knowledge, have not previously been recognized. Then, we construct SU(2) symmetric Hamiltonians and explore the ground-state phase diagram in accordance with the SU(3)⊃SU(2)x(1) symmetry hierarchy. It is natural to treat the eight generators of the SU(3) symmetry on an equal footing; this approach is called the eight-fold way. We find that the spin spectral functions and spin quadrupole spectral functions share the same structure,provided that the elementary excitations are flavor waves at low energies, which serves as a clue to the eight-fold way. An emergent S=l/2 gapless quantum spin liquid is found to coexist with spin nematic order in one of the ground states.

                                                                                                                                                                                                                                                 

Time and place: 2019.4.30, 14:00 pm, Wuhan National High Magnetic Field Center B206

Presenter: Shula Chen

Title: Dilute Nitride Semiconductors and Its Application in Nanophotonics and Optospintronics

Abstract:Dilute nitride semiconductors, e.g. Ga(In)NAs and GaNP, have been another versatile III-V material system which receives extensive research interest. This is driven by their unique giant bowing effect, i.e. a small incorporation of N into GaAs and GaP enables not only a significant reduction of bandgap, but also decreased lattice constant to integrate with well-established Si-based nanotechnology, therefore holding promise in visible and infrared-ranged nanophotonic applications. I will present our recent results on the GaNAs nanowire lasers, where we for the first time demonstrated the near-IR lasing from such nanostructured dilute nitride materials. Via both alloy and cavity engineering, we achieved wide lasing wavelength tunability and modal switching, which presents GaNAs nanowires as promising candidate for future IR nanolasers. Next, the opto-spintronic properties of GaNAs will be introduced. We demonstrated a room temperature spin-photon interface based on the GaNAs nanopillar array, where a defect-mediated spin filtering mechanism leads to an efficient electron spin amplification by 1200% and achieves a high spin polarization degree up to 60% in single nanopillar at room temperature. These results provide an exciting alternative to realize room temperature nanosized spin laser for future quantum information technology.

                                                                                                                                                                                                                                                 

Time and place: 2019.4.24, 15:30 pm, Wuhan National High Magnetic Field Center B206

Presenter: Walter Escoffier

Title: Aperiodic quantum oscillations in the two-dimensional electron gas at the LaAlO3/SrTiO3 interface

Abstract:We investigate the transport properties of a high-mobility quasi-two-dimensional electron gas at the interface between two insulators LaAlO3 and SrTiO3. Since its first discovery in 2004, the electronic band structure derived from magnetotransport studies in different experimental conditions of temperature and magnetic field provided equivocal conclusions. Recently, the use of high magnetic field clearly revealed non 1/B-periodic magneto-resistance oscillations, as evidenced by a highly non-linear Landau plot (Landau level index versus 1/B). Among various scenarios, the Roth-Gao-Niu model provides a natural explanation for this effect, in relation with the magnetic response functions of the system. The experimental magneto-transport results are discussed jointly with dedicated theoretical DFT band-structure calculations, as well as with structural analysis of the interface using high-resolution scanning transmission electron microscopy.

                                                                                                                                                                                                                                                 

Time and place: 2019.4.17, 14:30 pm, Wuhan National High Magnetic Field Center B206

Presenter: Jian-Qiao Sun

Title: Multi-Objective Optimization of Structures

Abstract:In this talk, we discuss conflicting objectives of various structures in engineering and in nature. The multi-objective optimization problem (MOP) is then formulated. The solution methods for MOP in the literature are reviewed. In particular, we introduce a hybrid evolutionary algorithm and cell mapping method for the global solution of MOPs. Several examples are presented including a nonlinear control example, a case study of multi-objective structural-acoustic optimization, and an MOP design of airfoils.

                                                                                                                                                                                                                                                 

Time and place: 2019.4.16, 14:30 pm, Wuhan National High Magnetic Field Center B206

Presenter: Jian-Qiao Sun

Title: Data-Driven Modeling for Analysis, Fault Detection, Optimization and Control of Dynamic Systems

Abstract:In this talk, we review efforts of the past few decades in developing mathematical models for analysis, fault detection, optimization and control of various civil, mechanical and biological systems.  Examples with “small” number of data are first discussed. These include the data driven modeling of acoustic materials, fatigue life prediction of metallic structures, modeling, fault detection and control of HVAC systems in office buildings, and surgical outcome prediction.  The methods for data-driven research are discussed including statistical analysis, principal component analysis, correlation analysis and neural networks.  We then discuss the implications of the availability of “big” data.  We then review the recent advances of methods in artificial intelligence, and discuss their potentials and challenges for applications to civil and mechanical systems operating in complex environment.  An example of our preliminary study of fault detection of rotor dynamic systems with deep learning is then presented to conclude the talk.  It is hoped that this talk will stimulate the interests in artificial intelligence and its application to traditional engineering disciplines.

                                                                                                                                                                                                                                                 

Time and place: 2019.3.29, 15:00 pm, Wuhan National High Magnetic Field Center B206

Presenter: Enke Liu

Title: Topologically Enhanced Transverse Electronic Transport Effects in Magnetic Weyl Semimetal Co3Sn2S2

Abstract:Topological physical states originating from non-trivial band characters in momentum space have motivated increasing interests in the condense matter physics. The magnetic Weyl semimetals with magnetic monopoles of Berry curvature is expected to generate the gaint, intrinsic transverse transport effects. In this talk, I will present a quasi-two-dimensional, kagome-lattice magnetic Weyl semimetal Co3Sn2S2. The chiral-anomaly-induced negative magnetoresistance, ARPES and STM observations provide signatures of Weyl fermions in Co3Sn2S2. The intrinsic properties including anomalous Hall conductivity, anomalous Hall angle, anomalous Nernst effect, and transverse thermoelectric conductivity are observed experimentally to reach up to an order of magnitudes larger than common magnetic systems. Our study establishes kagome-lattice magnetic Weyl semimetal with an out-of-plane ferromagnetic order as a key class of materials for fundamental research and device applications under the connection of topological physics and spintronics/spin-caloritronics.

                                                                                                                                                                                                                                                 

Time and place: 2019.3.29, 9:30 am, Wuhan National High Magnetic Field Center B206

Presenter: Haihu Wen

Title: Topological Superconductivity in SrxBi2Se3 and Bi2Te3/FeTe0.55Se0.45 heterostructures

Abstract:Topological superconductor is a timely and frontier topic in condensed matter physics. Here we report superconductivity with twofold symmetry in some related materials. In Sr doped Bi2Se3, we find the nematic superconductivity from the c-axis transport measurements. Furthermore, we show the systematic study of scanning tunneling microscope/spectroscopy on SrxBi2Se3. We find that the surface Dirac electrons will simultaneously condense into the superconducting state within the bulk superconducting gap. We deposit Bi2Se3 thin film on the FeTe0.55Se0.45 substrate and get the proximity induced superconductivity. Within the vortex cores of FeTe0.55Se0.45, we observed the long sought discrete Caroli-de Gennes-Matricon bound states. By using the quasiparticle interference technique, we demonstrate clear evidence of twofold symmetry of the superconducting gap. The gap minimum is along one of the main crystalline axis following the so-called Δ4y notation. This is also accompanied by the elongated vortex shape. Our results reveal the direct evidence of superconductivity with two-fold symmetry in Bi2Se3 thin film.

                                                                                                                                                                                                                                                 

Time and place: 2019.3.28, 16:00 pm, Wuhan National High Magnetic Field Center B206

Presenter: Haihu Wen

Title: Iron-based superconductors

Abstract:The iron based superconductors are expected to have strong potential in electricity transport, high magnetic field and sensitive magnetic detection. One of the on-going frontier studies on iron based superconductors is about the pairing mechanism. The Fermi surfaces in different systems are extremely distinct: some have both electron and hole pockets, but others have only the electron pockets. Therefore there is no consensus yet about the pairing gap structure and pairing mechanism. We have conducted extensive STM/STS studies on many different iron based superconductors and try to explore a unified understanding of the pairing mechanism in all iron based superconductors.

                                                                                                                                                                                                                                                 

Time and place: 2019.1.4, 10:00 am, Wuhan National High Magnetic Field Center B206

Presenter: Feng Liu

TitleTopological dipoles and quadrupoles

Abstract:Topology offers us a unique dimension of designing solid-state materials. One famous example is the Quantum spin Hall effect (QSHE) where electrons of opposite spins propagate oppositely. The origin of QSHE comes from a geometric field strength in momentum space that is the so-called Berry curvature. Besides QSHE, the geometric vector potential whose curl yields the Berry curvature – the Berry connection, can induce an electric dipole even without Berry curvature. The topological electric dipoles result fractional surface charges that manifest as topological edge states, which are robust to defects and edge roughness. Furthermore, a pair of such the topological dipoles can form a high order multipole – quadrupole, which corresponds to the topological corner states. In this talk we will discuss a simple tight-binding model that possesses topological dipoles and quadrupoles in zero Berry curvature. Experimental realizations based on solid-state material and dielectric photonic crystal are proposed. Furthermore, we show that in a pure quadrupole phase, topological edge state is pseudo-spin polarized in general.

                                                                                                                                                                                                                                                 

Time and place: 2018.12.10, 16:00 pm, Wuhan National High Magnetic Field Center C204

Presenter: Zenghui Wang

Title: A Vibrant New World—Exploring New Physics and Materials with Nanoelectromechanical Systems (NEMS)

Abstract:The advent of low-dimensional nanostructures has enabled a plethora of new devices and systems.  Among them, nanoelectromechanical systems (NEMS) offers the unique capability of coupling the exquisite material properties found in these atomically-defined nanostructures with their mechanical degree of freedom, opening new opportunities for exploring exotic phenomena at the nanoscale.  In this talk I will discuss two such examples: 1) using an individual carbon nanotube as a nanoscale balance to study low-dimensional phase transition, 2) using multimode resonance in black phosphorus NEMS resonator to resolve the intrinsic anisotropy in these nanoscale crystals, and 3) studying Brownian resonance and nonlinear motion in MoS2 NEMS.

                                                                                                                                                                                                                                                 

Time and place: 2018.12.4, 9:30 am, Wuhan National High Magnetic Field Center B206

Presenter: Masayuki Hagiwara

Title: High Magnetic Field Sciences at AHMF in Osaka University

Abstract:I will talk about two topics studied in high magnetic fields at the Center for Advanced High Magnetic Field Science (AHMF) after brief introduction of our high magnetic field facilities and experimental apparatus.The first topic is “the spin multipolar excitations observed in åkermanite compounds Sr2CoB2O7 (B=Ge and Si)”. In these compounds, Co2+ ions have magnetic moments (S=3/2). These are magneto-electric multiferroic materials in which spontaneous electric polarization appears due to the d-p hybridization mechanism. The Sr2CoGe2O7, abbreviated as SCGO, has small magnetic anisotropy, while the Sr2CoSi2O7, abbreviated as SCSO, has large magnetic anisotropy. In SCGO, we observed a two-magnon spin excitation appearing above the saturation magnetic field (Hsat) in the electron spin resonance spectra. Owing to small anisotropy, this excitation has purely spin-quadrupolar nature, and hence its observation is possible by electric component of the light (electro-magnon) due to the spin nematic interaction in SCGO. On the other hand, we observed not only two-magnon but also three-magnon spin excitations above Hsat in SCSO. The three-magnon (spin-octupolar) excitation was observed due to large magnetic anisotropy which mixes magnetic dipole and quadrupole terms, resulting in making this excitation possible by magnetic component of the light. We discuss the similarity and difference in spin excitations between SCGO and SCSO.The second topic is “the high-field magnetization of the S=1/2 honeycomb-lattice antiferromagnet Cu2(pymca)3(ClO4) where pymca stands for pyrimidine-2-carboxylate”. Recently, a honeycomb-lattice magnet with bond-dependent exchange interactions has been extensively studied as the Kitaev model [3], but in this talk, I will present the studies on a simple Heisenberg honeycomb-lattice antiferromagnet. The magnetic susceptibility shows a broad peak near 25 K, and no long range order is observed down to 0.6 K in the specific heat measurements. The magnetization curve up to 70 T at 1.4 K shows three step-like increases. Assuming three different exchange bonds based on the structure, the calculated magnetization curve reproduces the observed one except for the magnetization near 70 T, where the observed magnetization indicates another step while the calculated magnetization becomes saturated. The relationship between the magnetization plateaus and exchange bonds is discussed based on the numerical calculations.

                                                                                                                                                                                                                                                 

Time and place: 2018.11.26, 14:30 pm, Wuhan National High Magnetic Field Center B206

Presenter: Olgerts Dumbrajs

Title: History and presentstate of gyrotrons

Abstract:Gyrotron is well recognized as a promising high-power millimeter-wave and terahertz source. They are capable of providing hundreds of kilowatts of power at microwave and millimetric wavelengths. I will start the talk with an introduction to the electromagnetic spectrum and the operating principle of gyrotron oscillator. In the electron cyclotron maser (ECM), the effective frequency is directly related to the magnetic field, namely, the strength of the magnetic field determines the radiation frequency. So, in the next part, I will explain the magnetic field required for a gyrotronto generate higher frequency waves. In the second part, I will introduce the development path of gyrotron. The conventional gyrotron oscillator was first built and is now still widely used in different laboratories. The coaxial cavity gyrotrons show many advantages, but the technical complexity is increased. To achieve higher operating frequency at a given magnetic field, gyrotrons can operate at harmonics modes, with an increased risk of mode competition. The advantages and challenges of such types of gyrotron will be illustrated. In the last, I will present the present theoretical work on gyrotrons at University of Latvia. 

                                                                                                                                                                                                                                                 

Time and place: 2018.11.15, 15:30 pm, Wuhan National High Magnetic Field Center B206

Presenter: Ulrich Zeitler

TitleQuantum Matter in High Magnetic Fields

Abstract:High magnetic fields are an extremely powerful tool to investigate, to control and to manipulate the quantum properties of matter. In this talk I will present some recent results in this domain obtained at the High Field Magnet Laboratory in Nijmegen, the Netherlands.I will start the talk with a general presentation of HFML-EMFL, the high-field facility in Nijmegen with static magnetic fields up to 38 T (45 T in the near future).  More specifically, I will present the status of our current and future magnets and the wide range of state-of-the art experiments offered to external users. In the second part I will present in some more detail two examples where we show how electron-electron interaction can spectacularly influence the high field magneto-transport properties of new low-dimensional material systems: Transition-metal dichalcogenides (TMDs) and oxide-based heterostructures.  

                                                                                                                                                                                                                                                 

Time and place: 2018.11.7, 10:00 am, Wuhan National High Magnetic Field Center B206

Presenter: Glenn S. Daehn

Title: Impulse Welding and Manufacturing: Methods and Opportunities

Abstract:Explosive-like impulse can do remarkable things. Impact welding, for example can produce very strong welds between wildly dissimilar metals in a solid-state process, avoiding the intermetallic compounds that often cause brittleness, and melting that can destroy microstructure and strength. Explosive forming can dramatically extend forming limits and can avoid presses and fixed dies. This presentation will discuss many ways that explosive-like methods can be used in conventional lab or factory environments. While these methods can offer vastly different pressure-time profiles with pressures ranging to GPa and time scales to tens of nanoseconds, all these methods offer opportunities very light equipment and enable new phenomena that can enable new methods of joining, forming, cutting and surface treatment.

After a brief, but broad introduction to impulse manufacturing, we focus on the use of the new methods of the vaporizing foil technique and laser impulse methods to enable solid-state welding. Modeling and simulation will be synthesized with experimental macroscopic and microstructural information. Efforts to further commercialize these methods will also be discussed.

                                                                                                                                                                                                                                                 

Time and place: 2018.9.3, 16:00 pm, Wuhan National High Magnetic Field Center C204

Presenter: Devashibhai Adroja

Title: Introduction to ISIS pulsed Neutron and Muon facility and simple science examples

Abstract:The ISIS pulsed neutron and muon source at the Rutherford Appleton Laboratory in Oxfordshire UK is a world-leading centre for research in the physical and life sciences. ISIS produces beams of neutrons and muons that allow scientists to study materials at the atomic level using a suite of instruments, often described as ‘super-microscopes’. It supports a national and international community of more than 2000 scientists who use neutrons and muons for research in physics, chemistry, materials science, geology, engineering and biology. From the original vision over 30 years ago, ISIS has become one of the UK’s major scientific achievements. As the world’s leading pulsed neutron and muon source. ISIS has changed the way the world views neutron scattering and muon spin rotation and relaxation, which provide microscopic and fundamental information on the complex many body systems. I will briefly introduce the neutron and muon techniques and discussed the production of neutrons and muons at ISIS facility. I will discussed neutron and muon instruments, data analysis software and present some recent science examples. The science examples will be focussed on the investigations of spin excitations in Fe-based superconductors and heavy fermion superconductors, spin wave investigation in mutliferroics materials, spin gap and spin wave investigation in Kondo insulators and magnetic excitations in molecular magnets. Further, I will discuss investigations of novel crystal structure using the high resolution neutron powder diffraction and magnetic structures using a cold neutron diffractometer and diffuse scattering investigations using a single crystal diffractometer. I will also show how muon technique is used to investigate elemental analysis. I will also present upgrade plan for excitations instruments. Further I will show new funding mechanism for Chinese user community to use ISIS Facility.

                                                                                                                                                                                                                                                 

Time and place: 2018.9.3, 10:00 am, Wuhan National High Magnetic Field Center B206

Presenter: Dmitry Smirnov

Title: When high magnetic fields meet optical spectroscopy: probing electronic structure and interaction effects in novel electronic and magnetic materials

Abstract:A magnetic field is one of the few fundamental thermodynamic parameters (alongside with temperature or pressure, for example) widely used in experimental condensed matter physics to probe or induce new states of matter. The magnetic field can be applied in situ in a highly controllable manner, reversibly and with perfect tunability. It lifts degeneracy of electronic orbital and spin states, breaks time reversal symmetry, introduces energy and length scales of quantum states that may result in establishing new field-induced order and quantum effects.

A review of recent experimental results obtained at the US National High Magnetic Filed Lab is given to demonstrate the aptitude of high-field magneto-spectroscopy methods in studying novel electronic and magnetic materials.  Illustrative examples from the portfolio of our research will include: (i) Probing and controlling excitons in monolayer transition metal dichalcogenides (MoSe2, WSe2) with high magnetic fields, (ii) infrared magneto-spectroscopy of Dirac (ZrTe5) and Weyl (NbP) semimetals, (iii) magneto-Raman probe of magneto-elastic coupling in a quasi-2D, frustrated quantum antiferromagnet SrCu2(BO3)2.

                                                                                                                                                                                                                                                 

Time and place: 2018.8.24, 16:00 pm, Wuhan National High Magnetic Field Center A319

Presenter: Ryuichi Shindou

Title: Theories of topological spin-nematic excitonic insulators in graphite under high magnetic field and transport scaling in disordered semimetals

Abstract:In the first part of my talk, I will argue that three-dimensional topological excitonic insulator is realized in graphite under high magnetic field. Graphite under high magnetic field exhibits consecutive metal-insulator (MI) transitions as well as re-entrant insulator-metal (IM) transition at low temperature. A part of the experiment was discovered more than 30 years ago, while the identities of the low-temperature insulating phases are still unclear by now. We identify these enigmatic insulator phases with excitonic insulator phases, where electron and hole pocket(s) form spin-triplet excitonic pairings. We show that the re-entrant IM transition in the graphite experiment can be naturally explained by an enhanced quantum spin fluctuation in the presence of smaller electron and hole pocket(s). We further argue that the odd-parity spin-triplet excitonic pairing reconstructs chiral surface Fermi arc state of electron and that of hole into a 2+1 massless surface Dirac fermion (topological excitonic insulator).

In the second part of my talk, I will talk about transport scaling theories in disordered Weyl semimetal. In electronic band structure of solid state material, two band touching points with linear dispersion (called as `Weyl node') appear in pair in the momentum space. When they annihilate with each other, the system undergoes a quantum phase transition from Weyl semimetal (WSM) phase to a band insulator (BI) phase. The continuous phase transition is recently discovered in solid state materials. The phase transition is described by a critical theory with a `magnetic dipole' like object in the momentum space. I will argue that the critical theory hosts a new disorder-driven quantum multicritical phenomena. Based on the renormalization group argument, we clarify transport scaling properties around the Weyl node around the quantum multicritical point as well as the direct phase line between BI and WSM phases.

                                                                                                                                                                                                                                                 

Time and place: 2018.7.11, 15:00 pm, Wuhan National High Magnetic Field Center C204

Presenter: Chenhao Jin

Title: Generation, transport and detection of pure valley currents in two-dimensional heterostructures

Abstract:Two-dimensional (2D) hexagonal materials provide a promising platform for valleytronics devices, owing to the convenient generation and manipulation of valley qubits. However, efficient generation of valley information carriers with long valley lifetime is difficult to achieve in single material due to intrinsic valley relaxation channels. Here we show that, such intrinsic limit can be overcome through combining two materials into a van der Waals heterostructure; and report both near-perfect generation efficiency of valley information carriers, as well as record-high valley lifetime. Furthermore, we demonstrate generation, transport, and spatial-temporal imaging of the valley currents in a single device, which opens up new exciting opportunities to realize novel spintronic and valleytronic applications.

                                                                                                                                                                                                                                                 

Time and place: 2018.7.4, 9:30 am, Wuhan National High Magnetic Field Center C204

Presenter: Jing Wang

Title: Chiral Majorana fermions from quantum anomalous Hall state

Abstract:The chiral Majorana fermion, a massless fermionic particle being its own antiparticle, could arise as a one-dimensional quasiparticle edge state of a two-dimensional topological states of quantum matter. The propagation of chiral Majorana fermions could lead to non-abelian braiding and may be useful in topological quantum computation. Despite intensive searches, the chiral Majorana fermion is still have to achieve.Recently, we propose to realize a two-dimensional chiral topological superconducting state from the quantum anomalous Hall plateau transition in a magnetic topological insulator thin film through the proximity effect to a conventional s-wave superconductor. Furthermore, we predicted the half-quantized plateau as smoking gun signature of chiral Majorana fermion. Remarkably, such half-quantized plateau has been observed in experiments as an evidence for chiral Majorana fermion edge state in the quantum anomalous Hall-superconductor system.

                                                                                                                                                                                                                                                 

Time and place: 2018.7.3, 9:30 am, Wuhan National High Magnetic Field Center B206

Presenter: Congjun Wu

Title: Quantum Dynamics – Space-time Crystal and Bethe String States

Abstract:We present recent works on two different aspects of quantum dynamics – symmetry and strong correlations. For the symmetry aspect, we propose a new concept of “space-time” crystal as a general framework for studying intertwined space-time periodic structures, which include both the static crystal and the Floquet lattice as special cases. A new mathematic structure of “space-time” group is constructed to describe the symmetries of a space-time crystal, which augments the space group with non-symmorphic operations involving fractional translations along the time domain: “time-screw rotation” and “time-glide reflection”. Classifications for the 1+1 D and 2+1D space-time crystals (groups) are completed, and their consequences on dynamic band structures will be discussed. For the strong correlation aspect, we have studied the real frequency response at high energy which is a hard problem of condensed matter physics. We studied the role of Bethe-string states in the quantum spin dynamics in antiferromagnetic spin chains in high magnetic fields based on algebraic Bethe ansatz via the form-factor formulae. Close to quantum criticality, the string excitations govern the quantum spin dynamics, whereas the fractional excitations, which are dominant at low energies, reflect the antiferromagnetic quantum fluctuations. These states have been recently observed in the electron-spin-resonance spectroscopy measurement on SrCo2V2O8. This work is helpful for experimental studies on spin dynamics in both condensed matter and cold atom systems beyond the low energy effective Luttinger liquid theory.

                                                                                                                                                                                                                                                 

Time and place: 2018.6.29, 14:30 pm, Wuhan National High Magnetic Field Center C204

Presenter: Fan Zhang

Title: Quantum Hall Effects in Transition Metal Dichalcogenides

Abstract:The family of atomically thin transition metal dichalcogenides (TMDs) is a rapidly rising star on the horizon of condensed matter physics and has already revealed a number of spin-valley-helicity coupled optical phenomena. More fascinatingly, our magnetotransport measurements have provided compelling evidence for the presence of a three-fold Q-valley degeneracy and a heavily massive G-valley in few-layer n-type and p-type TMDs, respectively. In this talk, I will discuss our recent experimental progress on quantum transport in few-layer TMDs, guided by our earlier theoretical predictions. Particularly, I will introduce that the Q valleys offer an unprecedented opportunity to realize the solid-state version of flavor SU(3) symmetry that has been rare in electron systems to date and to explore novel electromagnetic phenomena that can arise from the interplay between the emergent symmetry and electron-electron interactions. Surprisingly, electrons carry flavor-dependent electric dipole moments even at zero magnetic field, rendering a ferroelectric nematic phase, allowing electric-field manipulation of the flavors, and leading to the concept of flavortronics.

                                                                                                                                                                                                                                                 

Time and place: 2018.6.25, 10:00 am, Wuhan National High Magnetic Field Center B204

Presenter: Xiwen Guan

TitleQuantum liquids and quantum dynamics with interacting spins

Abstract:Spins, intrinsic degrees freedom carried by elementary particles, atomicnuclei and quasiparticles, are the main theme in the study of modern physics. The quantum systems of interacting electrons, bosons and fermions essen-tially involve in interacting spins, forming rich quantum many-body phenom-ena, such as quantum liquid, criticality and dynamics etc. In this talk, using exactly solvable models, I shall discuss the unique phenomena of spin chargeseparation, quantum collapse and revival in ultracold atoms and quantum devices of interacting spins. Our exact results provide precise understanding of fundamental physics at a many-body level.

                                                                                                                                                                                                                                                 

Time and place: 2018.6.22, 10:00 am, Wuhan National High Magnetic Field Center C204

Presenter: Haizhou Lu

Title: 3D Quantum Hall effect

Abstract:The discoveries of the quantum Hall effect have led to three Nobel prizes and the booming field of topological states of quantum matter. So far, the quantum Hall effect is observed only in 2D systems. We show that the Fermi arcs can give rise to a distinctive quantum Hall effect in topological semimetals in three dimensions. Topological semimetals are 3D topological states of matter, in which the energy bands touch at a finite number of Weyl nodes. They host topologically-protected surface states, known as the Fermi arcs. Via a “wormhole” tunnelling assisted by the Weyl nodes, the Fermi arcs at two opposite surfaces can form a single 2D electron gas and support a quantum Hall effect in three dimensions. Possible signatures of the 3D quantum Hall effect have been observed in several experiments on the topological Dirac semimetal Cd3As2. Our discovery of this 3D quantum Hall give an example of (d-2)-dimensional boundary states, a promising direction in topological states of quantum matter.

                                                                                                                                                                                                                                                 

Time and place: 2018.5.21, 10:00 am, Wuhan National High Magnetic Field Center C204

Presenter: Likai Song

TitleEPR Applications in Biology: Examples from HIV Membrane Protein gp41 and an Antimicrobial AApeptide

Abstract:EPR is a powerful tool for biological research. The focus of this work is to develop EPR methods for characterizing biological samples, with specific aims to investigate HIV surface protein gp41 and an antibacterial peptide (AA1). 1). HIV gp41-antibody interaction at the viral membrane interface. The membrane proximal ectodomain region (MPER) of gp41 plays a critical role during the viral fusion process and is a major target of anti-gp41 antibodies and vaccine design. In this study, EPR and NMR techniques were used to define MPER structure on the membrane, MPER-lipid interaction, and how anti-HIV antibodies recognize their membrane-immersed epitopes. The analyses revealed a structurally conserved pair of helices immersed in the viral membrane separated by a flexible hinge. Neutralizing anti-gp41 antibodies disrupt the MPER hinge function by perturbing MPER hinge orientation, and/or extracting part of the MPER from the membrane. These findings have revealed important features of gp41-antibody interaction at the viral membrane interface. 2). Selective membrane disruption mechanism of an antibacterial AApeptide. AApeptides are a new class of antibacterial peptidomimetics that are not prone to antibiotic resistance and are highly resistant to protease degradation. We have characterized the membrane interaction of a lipo-cyclic-gamma-AApeptide (AA1). The analyses revealed that AA1 binding increases the membrane permeability of POPC/POPG liposomes, which mimic negatively charged bacterial membranes. AA1 binding also induces significant lipid lateral-ordering and membrane thinning. In contrast, minimal membrane property changes were observed upon AA1 binding for liposomes mimicking mammalian cell membranes, which consist of neutral lipids and cholesterol. Our findings suggest that AA1 interacts and disrupts bacterial membranes through a “carpet-like” mechanism.

                                                                                                                                                                                                                                               

Time and place: 2018.5.10, 10:00 am, Wuhan National High Magnetic Field Center B206

Presenter: Jurek Krzystek

TitleTerahertz Electron Paramagnetic Resonance

Abstract:The recent increase of interest in single-ion molecular magnets based on transition metal and lanthanides coordination complexes has necessitated developing techniques that reliably measure the parameter of importance for characterizing their properties, namely magnetic anisotropy, also known as zero-field splitting (zfs) for transition metals, or crystal-field splitting (cfs) for lanthanides and actinides. Whereas for many metal complexes High-Frequency and-Field EPR (HFEPR) has been fully adequate to determine zfs lying in the range of approximately 1-20 cm-1many of those that display single-ion magnet properties are characterized by so-called giant anisotropy, which means zfs or cfs exceeding, often significantly so, these numbers, sometimes reaching 100 cm-1, and more. In such a case, increasing the EPR operating frequency into terahertz range is necessary. An overview of available and prospective techniques that enable it will be presented together with applications.

                                                                                                                                                                                                                                               

Time and place: 2018.5.9, 15:00 pm, Wuhan National High Magnetic Field Center C204

Presenter: Zaiyao Fei

TitleEdge conduction and gate induced superconductivity in monolayer WTe2

Abstract:Topology and correlation are two essential concepts in modern condensed matter physics. They give rise to a lot of interesting phenomena and exotic ground states, among which the quantum spin Hall (QSH) effect and superconductivity are two famous examples. Monolayer WTe2, a topological nontrivial semimetal in the bulk form, has recently been predicted to be a QSH insulator if a bulk gap opens. In experiment, we find that at temperatures below about 100 K a gap appears and the 2D bulk becomes insulating near zero doping, while the edges remain conducting. At lower temperatures, the edge conduction is strongly suppressed by in-plane magnetic field. Most of the observations are consistent with monolayer WTe2 being a quantum spin Hall insulator. Surprisingly, when the monolayer is electrostatically doped away from the insulating state, the 2D bulk turns superconducting below about 1 K. Bilayer and trilayer WTe2, on the other hand, do not show any signature of edge conduction or superconductivity. Monolayer WTe2 thus provides a unique platform for studying different electronic ground states and the interplay among them.

                                                                                                                                                                                                                                                 

Time and place: 2018.4.27, 15:30 pm, Wuhan National High Magnetic Field Center B206

Presenter: Plamen Stanislavov Stamenov

TitlePoint Contact Andreev Reflection and the Measurement of Spin Polarization - High Fields and Novel Materials

Abstract:Following a very brief introduction to the research activities within the Magnetism and Spin Electronics Group at TCD, one topic of current development will be presented, as an example.

Point Contact Andreev Reflection (PCAR) is one of the few available methods for the determination of the Fermi level spin polarisation in metals and degenerate semiconductors. It has traditionally been applied at fixed (liquid He) temperatures, using pure niobium as the superconductor, and at essentially zero applied magnetic fields, all of which limit the amount of information that it can provide – i.e. do not allow for the extraction of the sign of the spin polarisation and make the assignment of the transport regime to ballistic or diffusive almost impossible.

Here a series of experiments is described, aimed at the expansion of this parameter space to higher magnetic fields and to higher temperatures. These require redesigned experimental setups and the use of higher performance superconductors. Demonstrations are described of the determination of the sign of the spin polarisation, at fields of more than 5-7 Tesla using a low-Z superconductor, as well as operations beyond 9.2 K. Doubts about the practical reliability of the PCAR technique are dispersed using systematic series of samples – the heavy rare-earths and comparisons with alternatives, such as spin-polarised field emission, photo-emission and Tedrow-Meservey tunnelling.

The specific material examples presented include 3d-metals, order-disorder transition alloys and zero-moment half-metals – Fe, FeAl and MnRuGa, alternative low-Z and high-Z superconductors – MgB2 and NbTi, and magnetic topological insulators, such as Cr- and V-doped (Bi1-xSbx)2Te3. Finally, remarks will be made towards the possibilities of using Andreev reflection in very high DC and pulsed magnetic fields.

                                                                                                                                                                                                                                                 

Time and place: 2018.4.4, 10:00 am, Wuhan National High Magnetic Field Center C204

Presenter: Jie Liu

TitleFractional Josephson effect in semiconductor superconducting wires

Abstract:The 4π-periodic Josephson effect is a distinguishing feature of a topological Josephson junction. However, stringent conditions make it hard to observe in experiments. In this work, we study the transient transport properties in a topological Josephson junction numerically. We show that the 4π Josephson current can be sustained under nonequilibrium conditions. The properties of the Josephson current are analyzed for different conditions and three main regimes are identified. First, when both the superconducting wires of the Josephson junction lie in the topologically nontrivial region, a 4π Josephson current can appear upon suddenly applying a dc voltage. Second, when one superconducting wire lies in the trivial region, while the other wire lies in the nontrivial region, the Josephson current is 2π periodic but the component of the higher-order Josephson current increases. Third, when both wires lie in the trivial region, a stable 2π Josephson current is observed. Most importantly, the fractional Josephson effect is fragile in the presence of disorder. Hence experiments should be designed carefully to eliminate the effect of disorder. These results could be helpful to optimize fine-tuning of the experimental parameters to observe the 4π-periodic Josephson current in a topological Josephson junction.

                                                                                                                                                                                                                                               

Time and place: 2018.3.29, 10:00 am, Wuhan National High Magnetic Field Center C204

Presenter: Simin Nie

Title: Topological nodal-line semimetals in ferromagnetic rare-earth-metal monohalides

Abstract:Topological semimetals, extending the topological classification from insulators to metals, have greatly enriched our understanding of topological states in condensed matter. This is particularly true for topological nodal-line semimetals (TNLSs). In the present paper, we identify layered materials as promising candidates for hosting TNLSs. Based on first-principles calculations and effective model analysis, we propose that layered ferromagnetic rare-earth-metal monohalides LnX (Ln=La, Gd; X=Cl, Br) exhibit long pursued topological phases. Specifically, single-layer LaX and single-layer GdX are ideal two-dimensional (2D) Weyl semimetals and large-gap 2D quantum anomalous Hall insulators (QAHIs), with band gaps up to 61 meV, respectively. In addition, 3D LaX and 3D GdX are TNLSs with a pair of mirror-symmetry protected nodal lines and 3D weak QAHIs, respectively. The nodal lines in 3D LaX extending through the whole Brillouin zone (BZ) are fairly robust against strong spin-orbit coupling (SOC) and located close to the Fermi level, providing a novel platform toward exploring the exotic properties in nodal-line fermions as well as related device designs.

                                                                                                                                                                                                                                               

Time and place: 2018.1.24, 10:00 am, Wuhan National High Magnetic Field Center C204

Presenter: Xiaoxiang Xi

Title: Superconductivity and charge-density-wave order in NbSe2

Abstract:Atomically thin van der Waals materials have emerged as a frontier for both fundamental physics and device applications. Although novel single-particle and excitonic properties have been extensively studied, the collective electron phenomena in these materials remain less well understood. In this talk, we will discuss superconductivity and charge-density-wave (CDW) order in atomically thin group-V transition metal dichalcogenide NbSe2 down to the monolayer limit. Electrical transport measurements show that the superconducting transition temperature decreases monotonically with reducing the layer thickness. The temperature dependent Raman scattering, on the other hand, shows enhanced CDW order as the sample thickness reduces. Magneto-transport measurements further reveal that the in-plane upper critical fields in atomically thin NbSe2 superconductors significantly exceed the Pauli paramagnetic limit. We will discuss possible mechanisms for these phenomena and electrical tuning of the superconductivity and CDW in this 2D metal.

                                                                                                                                                                                                                                                

Time and place: 2018.1.15, 9:30 am, Wuhan National High Magnetic Field Center C204

Presenter: Tiantian Zhang

Title: Double-Weyl Phonons in Transition-Metal Monosilicides

Abstract:We employed ab initio calculations to identify a class of crystalline materials of MSi(M=Fe, Co, Mn, Re, Ru) having double-Weyl points in both their acoustic and optical phonon spectra. They exhibit novel topological points termed “spin-1 Weyl point” at the Brillouin zone center and “charge-2 Dirac point” at the zone corner. The corresponding gapless surface phonon dispersions are two helicoidal sheets whose isofrequency contours form a single noncontractible loop in the surface Brillouin zone. In addition, the global structure of the surface bands can be analytically expressed as double-periodic Weierstrass elliptic functions.

                                                                                                                                                                                                                                                

Time and place: 2017.12.18, 14:30 pm, Wuhan National High Magnetic Field Center C204

Presenter: Wenyu Shan

Title: Model and Transport Studies on Topological Materials with Dirac Valleys

Abstract:Topological materials have attracted much recent interest from both theoretical and experimental sides. The existence of  Dirac valleys gives rise to exotic transport and optical properties. In this talk, I will focus on two types of systems with Dirac valleys: topological insulators and two-dimensional materials. For topological insulators, I will introduce the finite-size effect and the construction of effective model for thin film structure. For two-dimensional materials, I will discuss the recent puzzles on valley Hall experiments in graphene systems and our solutions. Furthermore I will talk about the generation and detection of pure valley current by optical approach in monolayer transition metal dichalcogenides.

                                                                                                                                                                                                                                                 

Time and place: 2017.12.6, 14:30 pm, Wuhan National High Magnetic Field Center C204

Presenter: Jinglei Zhang

Title: Measuring Quantum Oscillations in Extreme Magnetic Fields

Abstract:Measurement of quantum oscillations is a very powerful way for studying the Fermi-surface topologies. Recently, several techniques for probing the quantum oscillations had been successfully constructed in our Water-Cooled magnets with the highest field up to 38.5T and lowest temperature down to 0.3K. In this presentation, I will first explain the basic principles of these techniques and demonstrate their applications on topological materials. In the second part, I will discuss the effect of hydrostatic pressure on the magnetotransport properties of zirconium pentatelluride. We find that the quasi-linear magnetoresistance decreases drastically under pressure. Besides, the change of the quantum oscillation phase from topological nontrivial to trivial is revealed around 2.0GPa. Both demonstrate that the accidental Dirac cone in ZrTe5 is violated under pressure.

                                                                                                                                                                                                                                                 

Time and place: 2017.11.22, 9:30 am, Wuhan National High Magnetic Field Center C204

Presenter: Zhenbing Tan

Title: Toward quantum entanglement in solid state by Cooper pair splitting

Abstract:Quantum entanglement is at the heart of Einstein–Podolsky–Rosen (EPR) paradox, which is fundamental for quantum information. Quantum entanglement has been successfully realized in optics, where the experiment benefit from the easy generation of entangled photons. In solid state, however, the progress has been modest. One natural source for quantum entanglement in solid state is split Cooper pairs. A Cooper pair, split out from a superconductor into two different terminals, will form a non-local entangled spin pair. We report an experiment on a superconductor-graphene double quantum dot (QD) system, in which we observe Cooper pair splitting (CPS) up to a CPS efficiency of ~ 10%. Comparing to the previous Cooper pair splitters, we were able to independently tune the bias and the energy levels of the two graphene QDs. Benefit from that, for the first time, the energy levels of the two QDs were tuned to be asymmetric or symmetric with respect to Fermi level in the superconductor. And we observed CPS or elastic co-tunneling favored as predicted by current theories. The realization of CPS in graphene opens a door for graphene to be used for quantum information processing.

                                                                                                                                                                                                                                                 

Time and place: 2017.11.9, 14:30 pm, Wuhan National High Magnetic Field Center C204

Presenter: Jia Zhang

Title: Recent progress of first-principles calculations on advanced magnetic materials interface

Abstract:Spintronics is an emergent developing research field in condensed matter physics in which the electron charge, spin interact with each other. Especially various interesting phenomenon will arise with different functional magnetic materials interface and lead to potential device applications.In this talk I will discuss our recent first-principles calculations results on some advanced magnetic interfaces aiming at the low power consumption spintronics applications.

                                                                                                                                                                                                                                                 

Time and place: 2017.9.25, 14:30 pm, Wuhan National High Magnetic Field Center B206

Presenter: Kamran Behnia

Title: The challenge of efficient scientific communication

Abstract:A routine task of a contemporary scientist is to publish new findings in scientific journals. In general, one prefers to address the broadest possible audience by choosing a high-profile journal. On the other hand, the impact factor of a journal correlates with its rejection rate. This market-based process of scientific publication has become dominant in recent years.As a consequence, a considerable fraction of the time previously devoted to scientific research itself is nowadays spent in optimizing the quality of communicating the results of this research.

How to transform a scientific result to a scientific communication? How to manage to keep the quality of the initial ingredient during this transformation? I will try to address this issue with a focus on experimental condensed-matter physics. A few useful rules of thumb in addressing an ever-widening international scientific audience will be identified.

                                                                                                                                                                                                                                                 

Time and place: 2017.9.11, 10:00 am, Wuhan National High Magnetic Field Center B206

Presenter: Zheng Wang

Title: Structural and dynamical evolution in La-based glasses and melts

Abstract:The limited plasticity before catastrophic failure is a long-standing conundrum hindering the wide application of metallic glasses (MGs). Recent study found that the local relaxation behavior can strongly affect the heterogeneous deformation in MGs, which can even govern their mechanical performance at room temperature. Furthermore, the local relaxation behavior is also considered to be related to regions in MGs exhibiting weak bonding and large amount of free volume. Therefore, tuning the local relaxation behavior may provide a practical option to optimize the mechanical performance of MGs. For La-(Ni,Co)-Al MGs, replacing transition metals (TM) Ni and Co with similar sized Cu results in a different local relaxation behavior, where a separate beta-relaxation peak in the glass state vanishes. The reason behind it is still unclear yet but is suspected to be related with chemical interaction and local packing effects.

In this study, we measured density and total structure factor of these La-based glass-forming melts using the newly developed containerless electrostatic levitation (ESL), trying to find out some clue rooted in their liquid structures. We found interestingly a positive excess volume in the binary La-Cu melts, in contrast to the negative excess volume in La-Ni/Co melts. The La60Cu40 liquid exhibits also a considerably different total structure factor S(q) compared to that of the La60(Ni/Co)40 melts, measured with the X-ray synchrotron diffraction. Both the specific volume and the reverse Monte Carlo simulation on measured S(q) suggest a looser packing in La-Cu-(Al) than in La-(Ni,Co)-(Al) melts, which might be related to the change of the relaxation behavior in the ternary La-TM-Al glasses.

                                                                                                                                                                                                                                                 

Time and place: 2017.8.29, 10:30 am, Wuhan National High Magnetic Field Center B206

Presenter: Zhida Song

Title:Detecting the chiral magnetic effect by lattice dynamics in Weyl semimetals

Abstract:In the present work, we propose that the chiral magnetic effect, the direct consequence of the presence of Weyl points in the band structure, can be detected by its coupling to certain phonon modes, which behave like pseudo-scalars under point group transformations. Such coupling can generate resonance between intrinsic plasmon oscillation and the corresponding phonon modes, leading to dramatic modification of the optical response by the external magnetic field, which provides a way to study chiral magnetic effect by optical measurements.

                                                                                                                                                                                                                                                 

Time and place: 2017.6.9, 10:00 am, Wuhan National High Magnetic Field Center B206

Presenter: Gang Cao

Title:The Challenge of Spin-Orbit-Tuned Ground States in Iridates

Abstract:Effects of spin-orbit interactions in condensed matter are an important and rapidly evolving topic. Strong competition between spin-orbit, on-site Coulomb and crystalline electric field interactions in iridates drives exotic quantum states that are unique to this group of materials. In particular, the “Jeff = ½” Mott state served as an early signal that the combined effect of strong spin-orbit and Coulomb interactions in iridates has unique, intriguing consequences. In this talk, we survey some current experimental studies of iridates. In essence, these materials tend to defy conventional wisdom: absence of conventional correlations between magnetic and insulating states, avoidance of metallization at high pressures, “S-shaped” I-V characteristic, emergence of an odd-parity hidden order, etc. It is particularly intriguing that there exist conspicuous discrepancies between current experimental results and theoretical proposals that address superconducting, topological and quantum spin liquid phases. This class of materials, in which the lattice degrees of freedom play a critical role seldom seen in other materials, evidently presents some profound intellectual challenges that call for more investigations both experimentally and theoretically. Physical properties unique to these materials may help unlock a world of possibilities for functional materials and devices.

                                                                                                                                                                                                                                                 

Time and place: 2017.5.24, 10:00 am, Wuhan National High Magnetic Field Center B206

Presenter: Shuai Wei

Title:Glass Transition and Liquid-Liquid Transition in Phase-Change Materials and Bulk Metallic Glassformers

Abstract:Recent discoveries of three dimensional (3D) topological semimetals, including Dirac semimetals (DSM), Dirac nodal-line semimetals and Weyl semimetals, have generated immense interests since they represent new topological states of quantum matters. Both Dirac and Weyl semimetals feature relativistic fermions with linearly dispersing excitations. In this talk, I will first give a brief introduction to this emerging area and discuss how to characterize the properties of Dirac/Weyl fermions. Then I will present our recent studies on topological semimetals. I will show nearly massless Dirac fermions generated by 2D Sb layers coexists with ferromagnetism in Sr1-yMn1-zSb2, whichoffers a rare opportunity to investigatethe effect of time reversal symmetry breaking on the electronic band structure and explore a possible ferromagnetic Weyl state.I will also reportour recentdiscovery of two new nodal line semimetals – ZrSiSe and ZrSiTe. The nodal-line semimetals exhibit Dirac cones along a one dimensional line/loop in their electronic structure, contrasted with the Dirac/Weyl cones with discrete nodes in Dirac/Weyl semimetals. We have found signatures of nodal-line fermions from quantum oscillation experiments in these two materials and demonstrated that their atomically thin crystals are accessible via mechanical exfoliation, which raises the possibility of realizing the theoretically predicted 2D topological insulators in monolayers of ZrSiSe and zrSiTe. Finally I will discussexotic quantum transport behavior of Weyl semimetal YbMnBi2, which results from the zeroth Landau Level, a unique property of topological materials.

                                                                                                                                                                                                                                                   

Time and place: 2017.5.24,2:30-3:30 pm, Wuhan National High Magnetic Field CenterC204

Presenter:Zhiqiang Mao

Title:Relativistic Fermions Generated by Square Lattices in Layered Compounds

Abstract:Phase-Change Materials such as Ge2Sb2Te5 and Ge1Sb2Te4 can be reversibly switched between amorphous and crystalline states by applying an external voltage pulse. The fast phase switching on nanoseconds timescales is of technological interests for chalcogenide-based phase-change non-volatile memory devices for next generation data storage applications. A favored phase-change material must possess a unique combination of physical properties such as ultrafast crystallization kinetics, strong electronic/optical contrast, and relatively stable amorphous state. The urgency of understanding the underlying physics in the context of technological applications should need no emphasis. Here we show a striking anomaly in the viscosity of chalcogenide glass-forming alloy Ge15Te85. Applying the Adam-Gibbs equation to calorimetric data, we find a fragile-to-strong liquid transition (FS-transition), and then predict the ‘strong’ liquid course of the viscosity down to Tg. The in-situ X-ray scattering data reveal that the transition is not only related to short-range-order (SRO) structural change, but also linked to a remarkable development of medium-range-order (MRO). The latter manifests as an emerging pre-peak in total structural factor S(Q) and an atomic pair correlation on the length scale of ~8 Å in the real-space G(r) function. The FS-transition is also associated with a semiconductor-metal transition and a density anomaly. By examining the electronic conductivity and, then, semiconductor-to-metal (SC-M) transitions in related alloys, we find a systematic tendency in SC-M transitions with the metallicity of alloy components and conclude that Ge-Sb-Te Phase-Change Materials possess SC-M (and liquid-liquid) transitions that have become submerged below the liquidus surface, which controls the liquid-state behavior and has significant impact on application-relevant phase-change material properties.In parallel, we compare the liquid-state behavior of Ge15Te85 with that in the bulk metallic glass-forming liquid, Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 (Vit.106a), where a liquid-liquid transition(LLT) in the deeply undercooled state at T/Tg∼1.2 was observed using high-energy synchrotron x-ray radiation combined with electrostatic levitation (ESL). In the case of bulk metallic glassforming liquid, a quantitative structure-fragility relation can be applied and a FS-transition can be derived from the structural data.

                                                                                                                                                                                                                                                   

Time and place: 2017.4.14,10:00 am, Wuhan National High Magnetic Field CenterC204

Presenter:Jianming Lu

Title:The application of the field effect in low dimensional materials superconductors

Abstract:The characteristics of the material is closely related to the structure and height of Fermi surface, so It becomes an important means of material application and basic physics research to adjust Fermi surface or carrier concentration .Compared with the chemical doping, the traditional field effect transistors have less negative effects on impurities, avoiding the damage of sample eigen crystal structure; But the disadvantage is that the ability of adjusting Fermi surface is smaller, so often, only used in narrow band semiconductor metal insulator phase transition. In order to regulate the transformation of matter between various quantum states, such as the phase transformation from metal to superconducting state, we need a special kind of field effect of medium - ionic liquid: it inherits the traditional characteristics of the field effect that is not to introduce impurities, but the ability to adjust the carrier concentration is increased by an order of magnitude, which enables us to observe superconducting state in the semiconductor. Transition metal sulfide MoS2, for example, after entering the superconducting state, its unique structure of Fermi surface spin - valley "physical" - also be inherited to the superconductor, thus realized the Ising model superconducting state, having a significant impact on magnetic properties of the superconductor itself. In WS2 which has stronger spin orbit coupling , the superconducting state in single chemical vapor deposition of monolayer samples was observed, and the special insulators was found near superconducting phase space. Single-layer WS2 superconductor not only provide a ising superconductor paradigm, but also provide a new perspective for explaining the superconducting phase diagram induced by the widely observed multilayer samples and interfaces.

                                                                                                                                                                                                                                                   

Time and place:2017.2.14, 3:00pm, Wuhan National High Magnetic Field Center C204

Presenter:Wenbo Wang

Title:Characterization of ferromagnetic domains in magnetic thin films by using magnetic force microscopy

Abstract:Magnetic force microscopy (MFM) is a powerful scanning probe technique to study the local magnetic properties of sample surface, by detecting the magnetic interaction between the magnetic tip and sample. Here we present cryogenic MFM studies of a 200 nm thick hexagonal (h) LuFeO3film grown by molecular-beam epitaxy (MBE). Labyrinth-like domains ~ 1.8um in size were observed after zero field cooling below the Neel temperature TN~ 147 K, where weak ferromagnetic order (P63cm) exist. At 6 K, MFM images of the magnetization reversal process reveal a typical domain behavior of a pinning-dominated hard magnet. The pinning strength is substantially reduced at elevated temperature. The temperature dependence of the domain contrast demonstrates that our MFM is able to detect the domain contrast of magnets with tiny magnetic moments (~ 0.002 µB/f.u.). Taking advantage of this powerful MFM technique with high sensitivity, we were able to study the ferromagnetism of a quantum anomalous Hall system, Cr,V co-doped (Bi,Sb)2Te3. The magnetization reversal process reveals a typical ferromagnetic domain behavior, via domain nucleation and domain wall propagation. The carrier density dependence suggests both RKKY and non-RKKY-like interaction play an important role in the ferromagnetism of the magnetic topological thin films. Our results provide microscopic evidence of the ferromagnetic nature of a QAH system.

                                                                                                                                                                                                                                                   

Time and place:2016.12.19, 9:00am, Wuhan National High Magnetic Field Center B206

Presenter:Yixi Su

Title:monopoles and quantum dynamics in spin ice materials

Abstract:The realizations of magnetic monopoles as an emergent fractionalized quasi-particle in dipolar spin ice Ho2Ti2O7 and Dy2Ti2O7 pyrochlore compounds has been hailed as one of the major recent breakthroughs in condensed matter physics. Owing to the combination of a large Ising single-ion anisotropy and an effective ferromagnetic nearest-neighbor exchange interaction, the creation of magnetic monopoles as the consequence of the violation of the “2-in/2-out” ice rules becomes extremely energetically unfavorable below about 600 mK, thus leading to an almost completely suppressed spin dynamics and a frozen spin ice state possessing Pauling’s residual entropy. An intriguing question that thus arises and has already attracted tremendous amount of research efforts in the community is what may be the consequence if quantum fluctuation is invoked in the framework of the classical spin ice physics? Theories based on various forms of the quantum spin ice model have predicted the emergence of exotic ground state and collective excitations such as artificial photons. However, a convincing realization of the quantum spin ice state in real materials has not been achieved so far. In this talk, some of our recent neutron scattering studies of static and dynamics magnetic correlations in spin ice and quantum spin ice candidate materials based on frustrated pyrochlore oxides will be presented. Possible implication of our neutron scattering data within the context of the experimental signatures of magnetic monopoles and quantum dynamics will be discussed as well.

                                                                                                                                                                                                                                                   

Time and place:2016.11.1, 10:30am, Wuhan National High Magnetic Field Center B206

Presenter:Suchitra Sebastian

Title:Exploring Materials Universes: the case of an exotic insulator that behaves like a meta

Abstract:Materials comprise trillions of electrons that interact with each other to create a diversity of physical behaviours. We owe much of modern technology - from powerful computing to the marvels of communication - to discoveries of new types of collective electron behaviours in materials. Such discoveries, however, are often serendipitous, given that materials can be thought of as complex universes teeming with vast numbers of electrons, making their behaviours challenging to understand or predict. A question we are often confronted with is how to make progress in discovering novel collective electron behaviours akin to new universes. I will discuss possible approaches to increasing the odds of making discoveries, with examples from cases such as new superconductors and new types of dual metal-insulating materials. In particular, I will discuss the surprising case of the Kondo insulator SmB6 in which we have used high magnetic fields to observe a Fermi surface characteristic of a metal. Potential models will be discussed in the context of our findings.

                                                                                                                                                                                                                                                   

Time and place:2016.10.29, 9:00am, Wuhan National High Magnetic Field Center B206

Presenter:Hiroyuki Nojiri

Title:High Frequency EPR Studies for Low Dimensional Magnetic Systems

Abstract:Recent activities of the high frequency ESR on low dimensional magnetic systems will be introduced. In the first place, the ESR measuring systems in both pulsed and steady high magnetic fields will be presented. It will be followed by several examples on zero-dimensional magnetic systems such as hetero-metallic molecular magnets and high-spin giant magnetic clusters. In these compounds, ESR is used as the unique method to determine the magnetic levels and the short-range correlations. Moreover, the zero-field splitting and g-values are useful to identify the states of magnetic ions forming such clusters. For one-dimensional magnets, the development of the short-range correlation appears as the characteristic temperature dependence of the resonance field and the line width. The dimensionality also influence on the line shape of the resonance. A few examples will be introduced. Various examples of two-dimensional systems are also reviewed. The presentation includes the spin-ladder, the Shastry-Sutherland dimer system and perfectly frustrated two-dimensional dimer network. The spin gap excitation, triplets and the bound states are observed by the high frequency ESR. It will be summarized with a few comments on the expected developments of high frequency ESR.

                                                                                                                                                                                                                                                   

Time and place:2016.10.28, 10:30am, Wuhan National High Magnetic Field Center B206

Presenter:Vivien Zapf

Title:High Magnetic Fields for Multiferroics and Complex Functional Spin Systems

Abstract:I will review the need for new multifunctional magnetic materials, in particular insulating magnetoelectrics for low-power sensing, computing, and frequency devices. Complex magnetic spin systems are a route to creating magnetoelectric behavior by tuning the symmetry of the magnetism and creating key magnetoelectric coupling mechanisms. Understanding complex magnetic spin systems and how they couple to ferroelectricity in turn requires high magnetic fields and fast magnetic fields. High magnetic fields allows us to tune and explore materials to the extreme limits of their phase diagram and thereby distinguish among multiple models. Fast magnetic fields provide record sensitivity in magnetoelectric measurements as well as access to dynamic behavior. The combination of neutron diffraction, high and fast magnetic fields and theory allow us to understand complex spin systems and their multifunctionality. I will also discuss new routes to multiferroic behavior in metal-organic systems that go beyond traditional ferromagnetism and ferroelectricity.

                                                                                                                                                                                                                                                   

Time and place:2016.9.6, 9:00am, Wuhan National High Magnetic Field Center C204

Presenter:Rongjun Huang

Title:Proximity effect induced transport property between topological insulators (Bi2Se3, Sb doped Bi2Se3 ) and magnetic insulator CoFe2O4

Abstract:In this study, we mainly investigate the proximity effect in topological insulator and magnetic insulator bilayer system. In the experiment, Bi2Se3Sb/CoFe2O4 heterostructure was fabricated by using the molecule beam epitaxial technique and the pulsed laser deposition. A series of heterostructure magnetoresistances (MRs) are measured by physical properties measurement system (PPMS). The weak anti-localization (WAL) is strongly suppressed by the proximity effect in Bi2Se3Sb/CFO interface. The MR results are fitted by the modified HLN equation so that the size of surface state gap can be extracted successfully. The temperature dependent MR of the heterostructures at small and large perpendicular magnetic fields are also measured and analyzed. The results indicate that the phenomenon of surface band gap opening does not occur at small magnetic field because the CFO is in-plane magnetically polarized, but become manifest with increasing magnetic field. The approaches and results accommodated in this work show that CFO can effectively magnetizes Bi2Se3Sb and the heterostructures are promising for TI-based spintronic device applications.

                                                                                                                                                                                                                                                   

Time and place:2016.6.23, 3:00pm, Wuhan National High Magnetic Field Center C204

Presenter:Weiwei Zhao

Title:Research on quantum effects in the magnetic topological insulators and the low dimensional superconducting

Abstract:Anomalous quantum hall effect has attracted much attention in the experimental and theoretical research after confirmed by the experiment for the first time in 2013.Here I will introduce that in V doped magnetic topological insulators, the first observed zero resistance anomalous quantum hall effect under zero magnetic field and experimental evidence with lossless topology boundary condition (Nature Materials, 14473, Phys. Rev. Lett., 115057, 206).Superconductors as another kind of material of loss-less resistor, its low dimensional system have the rich quantum behaviors, these effects can be used for the carrier of future quantum computing and storage devices. Here I will introduce a few low dimensional quantum behavior research in the superconducting system, including the macroscopic quantum tunneling in superconducting nanowires, single magnetic flux switch, as well as (KTB phase transformation of superconducting thin films, vortex phase transformation, Ising pair of observation, etc.

                                                                                                                                                                                                                                                   

Time and place:2016.5.24.10am, Wuhan National High Magnetic Field Center B206

Presenter: Victor Pantsyrny

Title:High strength, high conductivity Cu matrix nanostructured composite wires processed by large plastic deformation

Abstract:New class of electrotechnical conductors on the base of nanostructured Cu-Nb alloy is under the consideration in this overview. It is known that anomalous increase of mechanical strength takes place in microcomposite Cu-Nb fine wires cold deformed by the drawing with large amount of deformation. The mechanisms of attaining of the extremely high mechanical strength at the level of 2000 MPa are discussed. The microstructure of heavily deformed Cu-Nb microcomposite consists of the ribbon like Nb filaments embedded in pure Cu matrix. The role of the specific structure of the interphases Cu-Nb boundaries is underlined. The interrelations of the mechanical strength and microstructure parameters such as the thickness of Nb ribbons are described. The decrease of the dislocation density during deformation was observed when the thickness of Nb ribbons and thickness of Cu matrix layers began to be comparable with the characteristic dimension of Frank-Read source of dislocation. It is also shown that the conductivity of nanostructured Cu-Nb materials is defined by the scattering of the electrons on the interphases Cu-Nb boundaries when the thickness of Cu matrix layers attain the mean free path of electrons in copper. The possibility to attain the high combination of conductivity in the range of 40% IACS to 80%IACS and Ultimate Tensile Strength in the range of 800 MPa to 1600 MPa in technical wires is presented. The examples of the high strength nanostructured technical Cu-Nb conductors with cross sections from 0.0007 mm2 (diameter of 30 µm) up to 120 mm2 are presented.

                                                                                                                                                                                                                                                   

Time and place:2016.5.23, 3:00pm, Wuhan National High Magnetic Field Center C204

Presenter:Yaomin Dai

Title:Non-Fermi liquid behaviors in Fe-based superconductors

Abstract:The normal state of high-temperature (high-Tc) superconductors is very unusual, with the electrical resistivity (or quasiparticle scattering rate) varying with temperature in a peculiar way that deviates significantly from the quadratic T dependence expected from Landau’s Fermi liquid (FL) theory of metals. We study a series of LiFe1−xCoxAs compounds with different Co concentrations by transport, optical spectroscopy, angle-resolved photoemission spectroscopy, and nuclear magnetic resonance. We observe a Fermi-liquid to non-Fermi-liquid to Fermi-liquid (FL-NFL-FL) crossover alongside a monotonic suppression of the superconductivity with increasing Co content. In parallel to the FL-NFL-FL crossover, we find that both the low-energy spin fluctuations and Fermi surface nesting are enhanced and then diminished, strongly suggesting that the NFL behavior in LiFe1−xCoxAs is induced by low-energy spin fluctuations that are very likely tuned by Fermi surface nesting. Our study reveals a unique phase diagram of LiFe1−xCoxAs where the region of NFL is moved to the boundary of the superconducting phase, implying that they are probably governed by different mechanisms.

                                                                                                                                                                                                                                                   

Time and place:2016.5.16, 3:00pm, Wuhan National High Magnetic Field Center B206

Presenter:Marcelo Jaime

Title:Magnetoelastic Correlations, Frustration, and Bose-Einstein Condensation in Quantum Magnets

Abstract:Quantum magnets are natural realizations of gases of interacting bosons whose relevant parameters such as dimensionality, lattice geometry, amount of disorder, nature of the interactions, and particle concentration can vary widely between different compounds. The particle concentration can be easily tuned by applying an external magnetic field which plays the role of a chemical potential. This rich spectrum of realizations offers a unique possibility for studying the different physical behaviors that emerge in interacting Bose gases from the interplay between their relevant parameters. The plethora of other bosonic phases that can emerge in quantum magnets, of which the Bose-Einstein condensate is the most basic ground state, is intriguing and not always easy to predict [1]. Here we review recent results with some attention paid to the strength of magnetoelastic correlations in quantum magnets as a smoking gun for frustration and broken symmetries crucial to determine the nature of the ground state.

                                                                                                                                                                                                                                                   

Time and place:2016.5.10, 3:00pm ,Wuhan National High Magnetic Field Center C204

Presenter:David C. Larbalestier

Title:The National High Magnetic Field Laboratory HTS conductor and magnet R&D program

Abstract:The NHMFL has been encouraged by two National Research Council Reports, COHMAG in 2004 and MagSci in 2013, to develop new generations of high field magnets using HTS materials. For much of the first 5 or 6 years [1] the emphasis was primarily on conductor evaluation and development and on small coils [2] but this led to the construction of a 32 T all superconducting coil from REBCO coated conductor that is almost ready for users. However REBCO coated conductors have large magnetization currents that are less desirable for uniform field applications than a multifilament, round, twisted, isotropic conductor like round wire Bi-2212. Recent developments of Bi-2223 laminated with superalloy also bring it back into contention as a high field magnet conductor. I will describe some elements of our program, including the recent 40 T no insulation insert coil (9T in 31T).

                                                                                                                                                                                                                                                   

Time and place:2016.5.10, 10:00am, Wuhan National High Magnetic Field Center C204

Presenter: Laura H. Greene

Title:High-Temperature Superconductivity: From History to Mystery

Abstract:At we pass the centenary of the discovery of superconductivity, the design of new and more useful superconductors remains as enigmatic as ever. As high-density current carriers with little or no power loss, high-temperature superconductors (HTS) offer unique solutions to fundamental grid challenges of the 21stcentury and hold great promise in addressing our global energy challenge in energy production, storage, and distribution. Traditionally guided by serendipity, our recent materials genome initiative is geared to develop predictive design of HTS. In this pursuit, we have chosen point contact spectroscopy (PCS) to aid in identifying promising candidates; as we have proved PCS to be an identifier of non-Fermi liquid (NFL) behavior above Tc, ubiquitous to all unconventional superconductors. We present a new definition of unconventional superconductivity; that the electronic fluid in the normal state is NFL, and that not necessarily the superconducting order parameter breaks the symmetry of the underlying lattice. We present how these studies will help to categorize and identify promising new HTS candidates.

                                                                                                                                                                                                                                                   

Time and place:2016.5.10, 5:00pm, Wuhan National High Magnetic Field Center C204

Presenter:Faxian Xiu

Title:Field-driven phase transition and magneto-optical properties in topological Dirac semimetals

Abstract:In this talk, I will first report the Landau level splitting in TDS Cd3As2single crystals under high magnetic fields (up to 60T), which suggests the removal of spin degeneracy by breaking time reversal symmetry. The detected Berry phase develops an evident angular dependence and possesses a crossover from nontrivial to trivial state under high magnetic fields, a strong hint for a fierce competition between the orbit-coupling and the field-generated mass term. Then, I will briefly review our recent progress in chiral anomaly by showing exclusively new approaches to detect the chiral anomaly and the related valley transport in ultra-high mobility Cd3As2Dirac semimetal. Three independent evidences including the E∙B-generated magneto-optical Kerr effect, the negative MR, and the valley transport, are provided as a direct and convincing experimental identification for the chiral anomaly in crystals. Finally, I would like to talk about the magneto-optical measurements in Cd3As2/ZrTe5Dirac semimetals and some exciting transport measurements under ultra-high magnetic field, in which a striking topological phase transition takes place (around 30 T), i.e., the dynamical mass generation. The Dirac electron spontaneously acquires a Dirac mass due to electron-electron interactions. These transitions also manifest themselves as spin density waves in both first and zeroth Landau levels. Our study presents the very first example of the dynamical mass generation phenomenon occurring in three-dimensional massless Dirac fermions in condensed matter physics.

                                                                                                                                                                                                                                                   

Time and place:2016.4.15, 2:30pm, Wuhan National High Magnetic Field Center C204

Presenter:Ke Zou

Title:Structural studies of high Tc superconductor FeSe/SrTiO3 grown by molecular beam epitaxy

Abstract:The marked enhancement of the superconducting critical temperature for FeSe grown on SrTiO3 (STO) is a notable recent discovery in the field of high temperature superconductivity. A complete understanding of the mechanism for this enhancement has not been elucidated and is thought to be due to how the electronic structure is modified by the interface. We determine the surface reconstruction of SrTiO3 that is used to achieve superconducting FeSe films in experiments. In particular, we observe the existence of a double TiO2 layer and identify the symmetry of the reconstruction at the FeSe/SrTiO3 interface. The double TiO2 layer plays two important roles. First, it facilitates epitaxial growth of FeSe films. Second, ab initio calculations reveal that electron transfer to the FeSe is enhanced by the double layer termination more strongly than by other surface structures of SrTiO3 . The enhanced electron transfer suppresses the hole pocket near the Γ point, leading to a band structure characteristic of superconducting samples. The characterization of the interface structure presented here is a key step towards understanding the electronic properties of this novel superconductor.

                                                                                                                                                                                                                                                   

Time and place: 2016.4.1, 3:00pm, Wuhan National High Magnetic Field Center C204

Presenter: Hongtao Yuan

Title:Electronic Phase Control with an Electric Field

Abstract:Electric-field control of charge carrier density has attracted much attention since it is remarkably simple for modulating physical properties of condensed matters and for exploring new functionalities with a transistor configuration. To realize novel field-effect modulated electronic phenomena in solids, a broad range of attainable carrier density is always required. However, so far, owing to the limitation of dielectric breakdown in most solid dielectrics, the maximum carrier density accumulated in conventional field-effect transistors (FETs) is quite low (<< 1013 cm-2) and thus seriously limits the tunability of electronic states of solids, for example, not sufficient enough to induce insulator-to-superconductor transition. While, recently a new type of transistor, known as electric-double-layer transistor (EDLT), with ionic liquids (ILs) as gate dielectrics have been proved to be able to effectively attain a high carrier density up to levels of around 1015 cm-2 and to realize a large local electric field up to 50mV/cm at liquid/solid interfaces, which are attracting increasing interests because of their potential to greatly tune electronic states and even to create novel states of matter which are impossible or difficult to obtain in conventional methods. In this presentation, I will discuss the interfacial carrier accumulation within liquid gated EDLTs and their novel tunability of varied electronic phase transitions in oxides, chacogenides and Dirac materials like graphene and topological insulators. I will start with fundamentals of interface electrochemistry and charging mechanism in such fantastic liquid/solid EDL interfaces, for example the competation between electrochemistry charging and electrostatic charging, or the interfacial band alginment and band engineering confirmed with measuring working functions of different ILs by photoemmision spectroscopy (PES). Based on these investigations and by further taking great advantages of high carrier density at EDL interfaces (1015 cm-2), we successfully obtained electric-field-induced insulator-metal transition in ZnO and insulator-superconductor transition in SrTiO3, KTaO3 and ZrNCl. Also we achieved carrier-mediated room temperature ferromagnetism in diluted magnetic semiconductors and giant anomalous Hall effect in magnetically doped topological insulators through modulating the interfacial carrier accumulation. On the other hand, by taking the advantage of large local electric field (50MV/cm), spin-orbit interaction (SOI) and resulting spin splitting of energy band of 2D systems can be regulated with structure inversion asymmetry (SIA) originated from the interfacial band bending and large applied electric fields, and further be used for generating spin-polarized carriers in solids.

                                                                                                                                                                                                                                                   

Time and place: 2016.3.24, 9:30am, Wuhan National High Magnetic Field Center C204

Presenter: Zhaoming Tian

Title:Exotic topological states and quantum metal-insulator transition in Nd2Ir2O7 pyrochlore iridates

Abstract:Pyrochlore iridates have attracted great interest as prime candidates to host topologically nontrivial states, quantum spin liquid state and quantum phase transition, in particular through the interplay between different degrees of freedom, such as local moments and mobile electrons. Based on our study using our high quality Nd2Ir2O7 single crystals, we will discuss such example, i.e. quadratic band touching state, Weyl semimetallic state and field-induced quantum phase transition in Nd2Ir2O7 pyrochlore iridates.

                                                                                                                                                                                                                                                   

Time and place: 2015.12.28, 10:00am, Wuhan National High Magnetic Field CenterC204

Presenter: Feng Wang

Title:Exploiting lanthanide luminescence in core-shell nanoparticles

Abstract:In this talk, I systematically introduce our recent efforts on lanthanide-doped core-shell nanoparticles that are generally composed of a layer-by-layer structure with a set of lanthanide ions incorporated into separate layer. I discuss how to fabricate these nanostructures by wet-chemistry method and how to characterize the nanostructure by a combination of electron microscopy and luminescence spectroscopy. Examples will be given to demonstrate highly flexible luminescence processes across UV to NIR spectral region in single core-shell nanoparticles by controlling the dopant composition and distribution of dopant ions in the host lattice. The enhanced ability to manipulate photon energy opens up exciting new opportunities for technological applications.

                                                                                                                                                                                                                                                   

Time and place:2015.10.29, 4:00pm, Wuhan National High Magnetic Field CenterB206

Presenter:Xiao Hu

Title:Questing after Majorana Particles in Topological Matte

Abstract:A Majorana particle is a fermion and equivalent to its antiparticle, which was proposed by E. Majorana in 1937 in order to explain the neutrino. While not yet confirmed as an elementary particle for about 80 years, physicists are excited recently by its presence in matters, since quasiparticle excitations in topological superconductors behave in the way with “particle being equivalent to antiparticle”, known as the Majorana condition. These Majorana quasiparticles (MQPs) are considered to be useful for realizing decoherence-free quantum computation. In this talk, I will introduce our recent work on search of MQPs in a topological superconductor formed by a topological insulator and a conventional s-wave superconductor. We reveal that, in the spin-resolved spatial-energy distribution of local density of states, there is a checkerboard-like pattern associated with MQP due to the intimate relation among the orbital and spin angular momenta and the phase winding of superconducting vortex. This, if measured successfully by the spin-resolved STM/STS, provides evidence for the long-searched-for Majorana particle.

                                                                                                                                                                                                                                                   

Timeand place: 2015.10.28, 10:00am, Wuhan National High Magnetic Field CenterB206

Presenter: Cyril Proust

Title:Fermi surface reconstruction by charge order in the pseudogap phase of underdoped copper oxides

Abstract:Over the last years, quantum oscillation measurements have shown that the Fermi surface of underdoped cuprates suffer a drastic modification compare to the large hole-like cylinder observed in the overdoped side. Many studies such as NMR measurements, x-ray scattering point to a reconstruction of the Fermi surface due to charge density wave (CDW). Fermi-surface reconstruction and charge modulations are two universal signatures of underdoped cuprates, which begs the following questions: what is the impact of charge order on the electronic properties of underdoped cuprates? Is the Fermi surface seen by quantum oscillations compatible with a reconstruction by CDW modulations?

After an introduction starting from the observation of quantum oscillations to the discovery of charge order in cuprates, I will present thermodynamic and transport measurements in underdoped cuprates performed in high magnetic fields demonstrating that a phase transition takes place at low temperature. Compelling evidence that the Fermi surface of YBa2Cu3Oyis reconstructed by the CDW order detected by x-ray diffraction comes from the recent discovery of an additional small hole-like pocket in quantum oscillations measurements. The consistency between our quantum oscillation measurements and models of Fermi-surface reconstruction by the CDW order will be discussed.

                                                                                                                                                                                                                                                   

Time and place:2015.10.26, 10:00am, Wuhan National High Magnetic Field CenterB206

Presenter:Amr S. Helmy

Title:Nano Photonic Architectures for Novel Communications and Sensing Technologies

Abstract:Plasmonic waveguides provide the unique ability to confine light within a few nanometers and allow for near perfect transmission through sharp bends as well as efficient light distribution between orthogonally intersecting waveguide junctions. However, due to free-carrier absorption in the metal, the enhanced mode confinement inevitably entails an increase in the waveguide loss. This lowers the device figure-of-merit achievable with passive plasmonic components and in turn hinders the performance of active plasmonic components. In order to mitigate the losses of these waveguides; a novel methodology for designing multi-layer hybrid plasmonic waveguides has been developed. This class of modes and the design methodology associated charts a route for obtaining modes with propagation loss values in the range of 5-10 dB/mm, while maintaining mode areas that are characteristic of plasmonics. This long range mode behavior empowers a new class of optical devices such as modulators, and detectors with record device sizes and parasitic capacitance values. With these structures as a building block, new levels of optoelectronic integration and performance metrics for athermal transceivers is achievable.

                                                                                                                                                                                                                                                   

Time and place:2015.10.15, 8:30am, Wuhan National High Magnetic Field CenterB206

Presenter:Johan Vanacken

Title:High Temperature Superconductors in Pulsed High Magnetic Fields

Abstract:Solid-state physics is investigated in high pulsed magnetic fields of B=50 Tesla and above. High magnetic fields are a basic research tool in contemporary condensed matter physics. In many cases, higher magnetic fields improve the understanding of physical phenomena or are even the only way to reveal them.

In this presentation the work done at the high field laboratory in Leuven on high temperature superconducting cuprates and pnictides) will be reviewed. The high field results of hole and electron doped (collaboration IOP - Beijing) cuprates will be presented, as well as the results on the pnictides (Collaboration Nanjing University).

The presentation will show mainly experimental work, stimulating theoreticians to work on the understanding of the complex behavior of high temperature superconductors.

                                                                                                                                                                                                                                                   

Time and place:2015.10.14, 8:30am, Wuhan National High Magnetic Field CenterB206

Presenter:Greg S. Boebinger

Title:Materials, Energy and Life: Entertaining Aspects of High Magnetic Field Research

Abstract:The MagLab exists to provide its international user community with unique magnets and expertise spanning condensed matter physics, materials research, chemistry, biochemistry, biology, and biomedicine. We generate magnetic fields exceeding two million times the Earth’s magnetic field. This talk seeks to answer the question, “Why would anyone want to do such a thing?” Illustrative examples from the portfolio of user research at the MagLab will include • MATERIALS:tweaking macroscopic quantum phenomena in two-dimensional square lattices of copper and oxygen to achieve high-temperature superconductivity or magnetic Bose-Einstein condensation;• ENERGY:analyzing nature’s most complex fluids, including petroleum, to improve utilization and mitigate pollution;and • LIFE:tracking sodium and gadolinium quantum dots to revolutionize magnetic resonance imaging.During the talk, we anticipate that jokes will very likely be told. The portion of the talk that surveys my own work on high-temperature superconductivity uses magnetic fields to suppress the superconductivity…with a goal of revealing the Wizard who pulls the strings behind the curtain. This work is a collaboration with Scott Riggs, Oskar Vafek and Jon Kemper of the MagLab branch at Florida State University; Jon Betts, Al Bert Migliori and Fedor Balakirev of the MagLab branch at Los Alamos National Laboratory; and W. N. Hardy, Ruixing Liang and Doug Bonn of the University of British Columbia.





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