Fermi arc electronic structure and Chern numbers in the type-II Weyl semimetal candidate MoxW1-xTe2

It has recently been proposed that electronic band structures in crystals can 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 MoxW1-xTe2 may realize such a type-II Weyl fermion. Here, we first show theoretically that it is crucial to access the band structure above the Fermi level epsilon(F) to show a Weyl semimetal in MoxW1-xTe2. Then, we study MoxW1-xTe2 by pump-probe ARPES and we directly access the band structure > 0.2 eV above epsilon(F) in experiment. By comparing our results with ab initio calculations, we conclude that we directly observe the surface state containing the topological Fermi arc. We propose that a future study of MoxW1-xTe2 by pump-probe ARPES may directly pinpoint the Fermi arc. Our work sets the stage for the experimental discovery of the first type-II Weyl semimetal in MoxW1-xTe2.