Dirac semimetals $A_3Bi$ ($A$=Na,K,Rb) as $Z_2$ Weyl semimetals

TL;DR

This paper reveals that Dirac semimetals $A_3Bi$ possess a $Z_2$ Weyl semimetal structure due to a discrete symmetry, leading to distinct Weyl sectors with surface Fermi arcs and monopole features in Berry curvature.

Contribution

It introduces a novel interpretation of Dirac semimetals as $Z_2$ Weyl semimetals based on a discrete symmetry of the effective Hamiltonian, with explicit calculations supporting this view.

Findings

Electron states split into two Weyl sectors.

Each sector exhibits Weyl nodes with Berry monopoles.

Surface Fermi arcs confirm the $Z_2$ Weyl semimetal nature.

Abstract

We demonstrate that the physical reason for the nontrivial topological properties of Dirac semimetals $A_3 Bi$ (A=Na,K,Rb) is connected with a discrete symmetry of the low-energy effective Hamiltonian. By making use of this discrete symmetry, we argue that all electron states can be split into two separate sectors of the theory. Each sector describes a Weyl semimetal with a pair of Weyl nodes and broken time-reversal symmetry. The latter symmetry is not broken in the complete theory because the time-reversal transformation interchanges states from different sectors. Our findings are supported by explicit calculations of the Berry curvature. In each sector, the field lines of the curvature reveal a pair of monopoles of the Berry flux at the positions of Weyl nodes. The $Z_2$ Weyl semimetal nature is also confirmed by the existence of pairs of surface Fermi arcs, which originate from different sectors of the theory.