Spin-orbit torques in a Rashba honeycomb antiferromagnet

TL;DR

This paper uses a microscopic model to analyze spin-orbit torques in a 2D Rashba honeycomb antiferromagnet, revealing how sublattice symmetry and disorder influence torque behavior and anisotropy.

Contribution

It provides a detailed numerical study of spin-orbit torques in a microscopic model, highlighting the effects of sublattice symmetry breaking and disorder on torque magnitude and symmetry.

Findings

Neel spin-orbit torque vanishes in symmetric model

Anti-damping torque becomes finite and anisotropic when symmetry is broken

Torque magnitude depends on impurity concentration

Abstract

Recent experiments on switching antiferromagnetic domains by electric current pulses have attracted a lot of attention to spin-orbit torques in antiferromagnets. In this work, we employ the tight-binding model solver, kwant, to compute spin-orbit torques in a two-dimensional antiferromagnet on a honeycomb lattice with strong spin-orbit interaction of Rashba type. Our model combines spin-orbit interaction, local s-d-like exchange, and scattering of conduction electrons on on-site disorder potential to provide a microscopic mechanism for angular momentum relaxation. We consider two versions of the model: one with preserved and one with broken sublattice symmetry. A non-equilibrium staggered polarization, that is responsible for the so-called Neel spin-orbit torque, is shown to vanish identically in the symmetric model but may become finite if sublattice symmetry is broken. Similarly, anti-damping spin-orbit torques vanish in the symmetric model but become finite and anisotropic in a model with broken sublattice symmetry. As expected, anti-damping torques also reveal a sizable dependence on impurity concentration. Our numerical analysis also confirms symmetry classification of spin-orbit torques and strong torque anisotropy due to in-plane confinement of electron momenta.