Measuring Chern numbers above the Fermi level in the Type II Weyl semimetal Mo_xW_1-xTe₂

2016/04/24 by Ilya Belopolski, Su-Yang Xu, Yukiaki Ishida +30 · 1 citation
Physics and Astronomy · #cond-mat.mes-hall

paper · pdf · doi:10.1103/physrevb.94.085127

published as Phys. Rev. B 94, 085127 (2016) · Incorporates earlier results presented in arXiv:1512.09099, by the same authors

arxiv created 2016/04/24 · arxiv updated 2016/08/24

Abstract

It has recently been proposed that electronic band structures in crystals give rise to a previously overlooked type of Weyl fermion, which violates Lorentz invariance and, consequently, is forbidden in particle physics. It was further predicted that Mo_xW_1-xTe₂ may realize such a Type II Weyl fermion. One crucial challenge is that the Weyl points in Mo_xW_1-xTe₂ are predicted to lie above the Fermi level. Here, by studying a simple model for a Type II Weyl cone, we clarify the importance of accessing the unoccupied band structure to demonstrate that Mo_xW_1-xTe₂ is a Weyl semimetal. Then, we use pump-probe angle-resolved photoemission spectroscopy (pump-probe ARPES) to directly observe the unoccupied band structure of Mo_xW_1-xTe₂. For the first time, we directly access states > 0.2 eV above the Fermi level. By comparing our results with ab initio calculations, we conclude that we directly observe the surface state containing the topological Fermi arc. Our work opens the way to studying the unoccupied band structure as well as the time-domain relaxation dynamics of Mo_xW_1-xTe₂ and related transition metal dichalcogenides.

Citations

• Unoccupied electronic structure and signatures of topological Fermi arcs in the Weyl semimetal candidate Mo_xW_1-xTe₂

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• Discovery of magnetic topological crystals