Prediction of an arc-tunable Weyl Fermion metallic state in Mo$_x$W$_{1-x}$Te$_2$

A Weyl semimetal is a new state of matter that hosts Weyl fermions as emergent quasiparticles. The Weyl fermions correspond to isolated points of bulk band degeneracy, Weyl nodes, which are connected only through the crystal’s boundary by an exotic Fermi arc surface state. The length of the Fermi arc gives a measure of the topological strength, because the only way to destroy the Weyl nodes is to annihilate them in pairs in k space. To date, Weyl semimetals are only realized in the TaAs class. Here, we propose a tunable Weyl metallic state in Mo$_x$W$_{1-x}$Te$_2$ via our first-principles calculations, where the Fermi arc length can be continuously changed as a function of Mo concentration, thus tuning the topological strength of the system [1]. Our results provide an experimentally feasible route to realizing Weyl physics in the layered compound Mo$_x$W$_{1-x}$Te$_2$ where non-saturating magneto-resistance and pressure driven superconductivity have been observed. \newline [1] T.-R. Chang et al., arXiv:1508.06723.