Probing $k$-Space Alternating Spin Polarization via the Anomalous Hall Effect

TL;DR

This paper introduces a novel method to probe $k$-space spin polarization in altermagnets by interfacing them with topological insulators, enabling measurement of local magnetic moments through the anomalous Hall effect.

Contribution

It proposes using topological insulator surfaces to detect $k$-space spin polarization in altermagnets, linking Dirac mass and Hall conductance to local magnetic moments.

Findings

Demonstrates how the Dirac mass relates to $k$-space magnetic moments.

Shows how Hall conductance measurements reveal spin density distribution.

Provides a method to map global magnetic moments in altermagnets.

Abstract

Altermagnets represent a recently discovered class of collinear magnets, characterized by antiparallel neighboring magnetic moments and alternating-sign spin polarization in momentum-space($k$-space). However, experimental methods for probing the $k$-space spin polarization in altermagnets remain limited. In this work, we propose an approach to address this challenge by interfacing an altermagnet with the surface of a topological insulator. The massless Dirac fermions on the topological insulator surface acquire a mass due to the time-reversal symmetry breaking. The local $k$-space magnetic moment at the Dirac point directly determines both the sign and magnitude of this Dirac mass, resulting in an anomalous Hall effect. By measuring the Hall conductance, we can extract the local $k$-space magnetic moment. Moreover, we can map the global magnetic moment distribution by tuning the Dirac point position using an in-plane magnetic field, thereby revealing the $k$-space spin density of the altermagnet. This work establishes the Dirac fermion on the topological insulator surface as a sensitive probe for unveiling spin characters of altermagnets and those of other unconventional antiferromagnets.