XXXVI Reunión Bienal de la Real Sociedad Española de Física

Observation of Large Topologically Trivial Fermi-Arcs in the Candidate Type-II Weyl Semimetal WTe2

18 Jul 2017, 18:30

20m

Aula Química Inorgánica (Facultad Química (USC))

Quantum Materials and Technologies (GEFES) Quantum Materials and Technologies (GEFES) I

Description

The discovery of non-saturating magnetoresistance and pressure induced superconductivity has drawn much attention to WTe2 lately. [1] The interest on this material increased when it was very recently proposed to be the first example of a new class of materials dubbed type-II Weyl semimetals.[2] The electronic band structure of a type-II Weyl semimetal shows tilted Weyl cones that arise from topologically protected crossings of valence and conduction bands causing touching points between electron and hole pockets near the Fermi level. The projection of these so called Weyl points onto a surface must be connected by Fermi arcs. In WTe2 the surface Fermi arcs terminate inside the bulk electron and hole pockets where the surface states strongly hybridize with bulk states and can no longer be observed experimentally. Additionally, WTe2 is non centro-symmetric, which implies inequivalent top and bottom surfaces with a distinct electronic structure that could not be resolved so far. Together, these subtleties render the identification of the topological nature of the Fermi arcs challenging. We present several advances towards a comprehensive understanding of WTe2 electronic structure. Using micro-focus laser-ARPES we resolve for the first time the distinct electronic structure of both inequivalent top and bottom (001) surfaces. The presence of large surface state Fermi arcs on both surfaces is established. [3] Using surface electronic structure calculations we further demonstrate that these Fermi arcs are topologically trivial and that their existence is independent of the presence of type-II Weyl points in the bulk band structure. Contrary to common believe, the observation of surface state Fermi arcs is thus not suitable to robustly identify a type-II Weyl semimetal. [4] Finally, we show that the bulk Fermi surface is formed by three-dimensional electron and hole pockets with areas that are found to be in good agreement with transport experiments with the exception of small hole pockets that have not been observed in quantum oscillation experiments. This work was supported by the Swiss National Science Foundation through the Ambizione grant (PZ00P2_161327)