Multiple fermions in MoP

Abstract

Based on the first-principles calculation, we report that the WC-type MoP is a new type of topological semimetal. It can host Weyl semimetal phase with six pairs of Weyl points (WPs) in the first whole Brillouin zone (BZ). In the absence of spin-orbit coupling (SOC), band inversion forms a gapless nodal ring protected by horizontal mirror symmetry [Formula: see text]. The strong SOC in MoP makes the nodal ring fully gapped in the mirror plane, and generates multiple WPs away from the plane. As one hallmark of Weyl semimetals, the unique Fermi arcs are also observed by calculating the projected surface states and Fermi surfaces. Besides the above prodigious features, it also possess an additional four pairs of massless fermions with triply degenerate points (TDPs) in the vicinity of the Fermi level. Each TDP is a band crossing between degenerate and non-degenerate bands along the high-symmetry line in the Brillouin zone, and is protected by crystalline symmetries. Such new type of topological semimetal realizes multiple fermions states and further provides a fancy platform to study emergent physical phenomena.