Multi-type Dirac fermions protected by orthogonal glide symmetries in a noncentrosymmetric system

TL;DR

This paper uncovers how orthogonal glide symmetries protect two distinct types of bulk Dirac points in noncentrosymmetric systems, exemplified by KSnSe2, revealing new topological phases and symmetry protection mechanisms.

Contribution

It introduces a novel symmetry protection mechanism for multiple Dirac fermion types in noncentrosymmetric materials and identifies KSnSe2 as a candidate for such topological phases.

Findings

Identification of two distinct Dirac point types protected by glide symmetries

Demonstration of a symmetry-enforced Dirac point at a non-time-reversal-invariant momentum

Proposal of KSnSe2 as a material hosting multi-type Dirac fermions

Abstract

Compared to inversion-symmetric systems, emerging bulk Dirac point (DP) in noncentrosymmetric systems is much harder and its symmetry protection mechanism is poorly understood. In this work, we propose that orthogonal glide symmetries can protect two distinct types of bulk anisotropic DPs. One is the ordinary anisotropic DP that is doubly degenerate only along one invariant axis, which is resulted from symmetry-protected accidental band crossing. The other one is a symmetry-enforced DP fixed at a non-time-reversal-invariant point, which is doubly degenerate at three orthogonal directions. This unique topological phase is exemplified by KSnSe$_{2}$ in space group 108. Our work not only unveils an unique symmetry protection mechanism but also provides the first material candidate for exploring multi-type Dirac fermions in noncentrosymmetric systems.