Research Progress

Topological semimetal in honeycomb lattice LnSI

author: time:2017-09-22 clicks:


(a)The A-A stacked honeycomb lattice. (b)The 3D strong TI. (c)Nodal-line semimetal with two nodal lines circled around the Γ point as shown in (d). (e)Topological semimetal coexisting of both Weyl nodes and nodal lines as shown in (f). (g)Double Weyl semimetal with two pairs of double-Weyl points. (h) Ideal Weyl semimetal holding four pairs of Weyl nodes.

(PNAS 2017, Doi:10.1073/pnas.1713261114)


Weyl semimetal (WSM), whose low energy excitation satisfies the Weyl equation exactly, has attracted considerable interest during the last few years. One hallmark of the WSM is the Weyl nodes (WNs) and the Fermi arcs existing at the crystal boundary. Recently, WNs and Fermi arcs were predicted and observed in the TaAs family of compounds. However, the complicated electronic structures in TaAs lead to many debates on the spectroscopic and transport properties, especially the origin of the negative magnetoresistance observed in it. Thus, it is desirable to find the ideal WSMs with less pairs of WNs residing at the Fermi level only.

What we discover?

In this work, we study a special 3D honeycomb lattice model with inversion symmetry broken and demonstrate that fruitful topological nontrivial states can be realized in such system, including ideal WSM, 3D strong topological insulator (TI), nodal-line semimetal, and a novel semimetal phase consisting of WNs and nodal lines, which is discussed for the first time in condensed matters. Furthermore, based on density functional theory(DFT) calculations, we show that rare earth-sulfide-iodide LnSI(Ln=Lu, Y, and Gd) satisfies this model well, among which LuSI and YSI are 3D strong TIs with unusual surface states of the right-handed spin texture, and GdSI is the long-pursued ideal WSM with only two pairs of WNs crossing the Fermi level. Two very long Fermi arcs exist on the (010) surface of GdSI, which are easily confirmed by angle-resolved photoemission spectroscopy (ARPES) experiment.

Why is this important?

Our work provides a new mechanism to explore the topological materials, especially the ideal WSM and nodal-line semimetal. The proposed ideal WSM GdSI gives a new platform for exploring the chiral anomaly physics and related device designs. Following our work, GdSI has already drawn some experimental groups’ attention. The corresponding experimental works are on-going.

Who did the research?

Simin Nie1,2, Gang Xu1,3,4, Fritz B. Prinz2, and Shou-cheng Zhang4

1Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China.

2Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305.

3School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China.

4Department of Physics, Stanford University, Stanford, CA 94305-4045.


This work is supported by the National Thousand Young Talents Program and the National Natural Science Foundation of China.

P. S.

Gang Xu returned to the Center in 2016 and was selected as National Thousand Young Talents Program of China in 2017. Xu’s researches mainly focus Materials Computation and condensed matter theory, including the topological materials and topological states such as Chern semimetal, quantum anomalous Hall (QAH) effect and topological superconductivity(TSC); the electronic structures and physical properties of the iron-based superconductors. More than 35 papers published on the high level international journals, including 8 PRL, 2 Nat. Nanotech, 1 Nat. Phys, 1 Nat. Commun and 2 Nano letters. Total citations are more than 4000. H-index=21. The detailed publications are at

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