Cubic Dirac fermion in quasi-one-dimensional transition-metal mono-chalcogenide

Abstract

We show that a previously predicted fermion particle that has no analogue in the standard model of particle theory, the cubically dispersed Dirac semimetal (CDSM), will exist in a specific, stable solid state system that has been made years ago, but was not appreciated to host such a unique fermion. Our prediction was derived by combining crystal symmetry with topological invariants and identified the space group P63/m as one of the two that can have a CDSM. We then conduct a material search using density functional theory identifying a group of quasi-one-dimensional molybdenum mono-chalcogenide compounds A(MoX)3 (A = Na, K, Rb, In, Tl; X = S, Se, Te) as ideal CDSM candidates. Studying the stability of the A(MoX)3 family reveals a few candidates such as Rb(MoTe)3 and Tl(MoTe)3 that are resilient to Peierls distortion, thus retaining the metallic character. The importance of this theoretical discovery is not only in identifying a unique, never before realized fermion type in actual materials, but also in the possibilities it opens for new material properties associated with Luttinger liquid and topological superconductivity.