Predicted Realization of Cubic Dirac Fermion in Quasi-One-Dimensional Transition-Metal MonoChalcogenides

TL;DR

This paper predicts and identifies a class of cubic Dirac semimetals in quasi-one-dimensional transition-metal mono-chalcogenides, revealing their unique symmetry-protected band crossings and potential for novel optical properties.

Contribution

It demonstrates the realization of cubic Dirac fermions in specific solid-state materials and identifies candidate compounds through density functional theory.

Findings

Cubic Dirac semimetal characterized by linear and cubic dispersions

Identification of Rb(MoTe)3 and Tl(MoTe)3 as stable candidates

Potential for polarization-dependent optical responses

Abstract

We show that the previously predicted Fermion particle that has no analogue in the standard model of particle theory - the cubically dispersed Dirac semimetal (CDSM) - is realized in a specific, stable solid state system that has been made years ago, but was not appreciated to host such a unique Fermion, composed of six Weyl Fermions, 3 with left-handed and 3 with right-handed chirality. We identified the crystal symmetry constraints and found the space group P63/m as one of the two that can support a CDSM, of which the characteristic band crossing has linear dispersion along the principle axis but cubic dispersion in the plane perpendicular to it. We then conducted 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 predicted to be resilient to Peierls distortion, thus retaining the metallic character. The combination of one-dimensionality and metallic nature in this family provides a platform for unusual optical signature - polarization dependent metallic vs insulating response.