Enhancing topological Weyl Semimetals by Janus transition-metal dichalcogenides structures

Abstract

The search and characterization of Weyl Semimetals (WSMs) is a challenge, in particular, because it requires a deep numerical analysis of the Fermi surface to identify the Fermi arcs. Here, we proposed a theoretical framework based on the combination of density functional theory with maximally localized Wannier functions for tight-binding parametrization and topological analyses to identify and characterize WSMs compounds. Inspired by the results reported for the transition-metal dichalcogenides (TMDs) compounds, namely, the WTe2 and MoTe2 systems, we selected the layered Janus-TMDs MTeSe (M = W, Mo, Cr) compounds in the 1T, 1T′, and 1Td structures to search for new WSMs. Based on phonons calculations, we found that only 8 Janus-TMDs are stable. The stacking 3D structure of the Janus-TMDs reveals a strong kz Fermi surface dependence. We report different Fermi surface k-planes behavior: (i) a point-like kind and (ii) a non-point like that are related to a cone and a tilted cone energy dispersion, respectively. From our results, we introduced a sub-classification inside the previous type II WSMs, namely, (i) strong type II if all Fermi surface k-planes present non-point like behavior and (ii) weak type II if one plane is point-like. As before, all planes with point-like Fermi surface stands for type I. Based on that, only one Janus-TMDs was found to be of type I, while the remaining systems are separated into two groups, namely, weak and strong type II. From our understanding, the planar Hall current experiments might be sensitive and able to distinguish the two sub-type II classification. From our calculations and analyses, the Janus structures exhibit Weyl points with a large separation in k-space compared with the pristine ones. This property is fundamental to obtain large extended Fermi arcs on the surface of the material and design good candidates for angle-resolved photoemission spectroscopy experiments.