Spin and anomalous Hall effects emerging from topological degeneracy in Dirac fermion system CuMnAs

TL;DR

This study reveals how topological features in CuMnAs lead to significant spin and anomalous Hall effects, with magnetic fields enabling the latter by breaking symmetry and lifting band degeneracies.

Contribution

It demonstrates the connection between topological band structures and transport phenomena in CuMnAs, highlighting the role of magnetic fields in inducing anomalous Hall effects.

Findings

Large spin Hall conductivity from nodal line gapping due to spin-orbit coupling.

Magnetic fields induce anomalous Hall effect by breaking symmetry.

External magnetic fields lift band degeneracy, enhancing Hall responses.

Abstract

Orthorhombic CuMnAs has been proposed as an antiferromagnetic semimetal hosting nodal line and Dirac points around the Fermi level. We investigate relations between the topological bands and transport phenomena, i.e. spin Hall effect and anomalous Hall effect, in orthorhombic CuMnAs with first-principles calculations combined with symmetry analysis of magnetic structures and of (spin) Berry curvature. We show the nodal line gapped with spin-orbit coupling in CuMnAs dominantly generates large spin Hall conductivity in the ground state. Although the magnetic symmetry in the ground state of CuMnAs forbids the finite anomalous Hall effect, applied magnetic fields produce a significant anomalous component of the Hall conductivity with the magnetic symmetry breaking. We identify that the dominant contribution to anomalous Hall components comes from further lifting of band degeneracy under external magnetic fields for the Bloch states generated with splitting of nodal lines by spin-orbit coupling near Fermi energy.