Discovery of a new type of topological Weyl fermion semimetal state in MoxW1-xTe2

A Type II Weyl fermion semimetal has been predicted in Mo x W1−x Te2, but it awaits experimental evidence. Here, Belopolski et al. observe a topological Fermi arc in Mo x W1−x Te2, showing it originates from a Type II Weyl fermion and offering a new platform to study novel transport phenomena in Weyl semimetals.