题目：Neutron Scattering Study of the Temperature-Dependent Phonon Spectra of AgSbTe2

Neutron Scattering Study on the Orbital-ordering and Itinerancy in a Frustrated Spinel Vanadate

主讲人:马杰 美国橡树岭国家实验室

讲座时间: 2015年1月8日上午9:30

讲座地点：国家脉冲强磁场科学中心B206

讲座摘要：

Neutron Scattering Study of the Temperature-Dependent Phonon Spectra of AgSbTe2

The thermoelectric material AgSbTe2 has attracted much attention due to the simple rocksalt structure, high thermoelectric figure-of-merit, and its extremely low thermal conductivity in bulk samples. Previous theoretical studies have suggested that the phonons can be scattered by anharmonicity (phonon-phonon coupling) and nano-defects in AgSbTe2. However, systematic measurements of the phonon spectra in this compound have not been available. We report our results of detailed time-of-flight and triple-axis neutron scattering measurements, as a function of temperature, and departure from stoichiometry. The temperature dependence of the phonon density-of-states, dispersion, and linewidth are discussed, and the lattice thermal conductivity in this system is calculated, which agrees with the reported value.

Neutron Scattering Study on the Orbital-ordering and Itinerancy in a Frustrated Spinel Vanadate

The crossover from localized- to itinerant-electron regimes in the geometrically-frustrated spinel system Mn1-xCoxV2O4 is explored by neutron-scattering measurements, first-principles caclulations, and spin models. At low Co doping, the orbital ordering (OO) of the localized V3+ spins suppresses magnetic frustration by triggering a tetragonal distortion. At high Co doping levels, however, electronic itinerancy melts the OO and lessens the structural and magnetic anisotropies, thus increases the amount of geometric frustration for the V-site pyrochlore lattice. Contrary to the predicted paramagentism induced by chemical pressure, the measured noncollinear spin states in the Co-rich region of the phase diagram provide a unique platform where localized spins and electronic itinerancy compete in a geometrically-frustrated spinel

个人简介：

2003年毕业于中国科学技术大学材料科学与工程系，获得理学学士学位；2010年于美国衣阿华州立大学天文与物理系获得凝聚态物理学博士学位；2010年至2015年在美国橡树岭国家实验室中子散射中心和田纳西大学天文与物理系担任博士后研究员；2015年入选第十一批“”青年人才，加入上海交通大学物理与天文系。长期从事凝聚态物理前沿实验研究方面的工作，尤其是运用中子散射及同步辐射X光技术对强关联体系功能材料的晶体结构、声子谱和磁子谱进行研究，探讨材料中电子、磁子、声子和轨道等相互作用及其导致的诸如电荷有序、轨道晶格耦合、自旋晶格相互作用等新奇量子效应和物理现象，以及这些效应对功能材料中各种性能的影响。已在Science, Nature Materials, Nature Nanotechnology, Physical Review Letters, Journal of the American Chemical Society等国际主流杂志上发表论文35篇。