Flavio Bruno1 A. Tamai1 I. Cucchi1 Q.S. Wu2 C. Barreteau1 A. de la Torre1 S. McKeown Walker1 S. Ricco1 Z. Wang3 T.K. Kim4 M. Hoesch4 M. Shi3 N.C. Plumb3 E. Giannini1 A. A. Soluyanov2 F. Baumberger1

1, University of Geneva, Geneva, , Switzerland
2, ETH Zurich, Zurich, , Switzerland
3, Swiss Light Source, Paul Scherrer Institute, Villigen, , Switzerland
4, Diamond Light Source, Didcot, , United Kingdom

In this talk we will discuss angle-resolved photoemission experiments resolving the distinct electronic structure of the inequivalent top and bottom (001) surfaces of WTe2 and MoTe2. We further use the identification of the two different surfaces to clarify the number of Fermi surface sheets presenting a unifying picture of the surface and bulk electronic structure of both compounds. We identify surface states on both surfaces, some of which form large Fermi arcs emerging out of the bulk electron pocket. All surface states observed experimentally are reproduced by electronic structure calculations. In the case of WTe2 the existence of Fermi arcs is independent of the presence of type-II Weyl points in the bulk band structure. This implies that the observation of surface Fermi arcs alone does not allow the identification of a material as a topological Weyl semimetal. However, the surface states observed in MoTe2 could only be reproduced by electronic structure calculations for the experimental crystal structure that predicts a topological Weyl semimetal state with eight type-II Weyl points. We further use systematic electronic structure calculations simulating different Weyl point arrangements to discuss the robustness of the identified Weyl semimetal state and the topological character of Fermi arcs in MoTe2.
F.Y. Bruno, et al, Phys Rev B 94, 121112(R) (2016).
A. Tamai, F.Y. Bruno, et al, Phys Rev X, 6, 031021 (2016).