Conductivity anisotropy and linear dichroism in spin-textured altermagnets

TL;DR

This paper demonstrates that spin textures in altermagnets induce tunable in-plane anisotropies in electrical and optical properties through emergent gauge fields, even without spin-orbit coupling, enabling polarization-resolved probing and directional electronic functionalities.

Contribution

It reveals how smooth spin textures create emergent gauge fields in altermagnets, leading to anisotropic transport and optical responses, a novel mechanism not previously explored.

Findings

Spin textures produce strong in-plane anisotropies in conductivity and absorption.

Optical anisotropy varies with frequency, locking to crystal axes at low frequencies and helix at high frequencies.

Polarization-resolved optics can directly probe textured altermagnetic states.

Abstract

Spin textures are ubiquitous in antiferromagnets, yet their consequences for altermagnets remain largely unexplored. We show that smooth spatial variations of the N\'eel order act on itinerant electrons as emergent gauge fields, producing strong, tunable in-plane anisotropies in dc transport and interband optical absorption, even without intrinsic spin-orbit coupling. As a concrete example, we analyze a coplanar spin helix and predict that the principal axes of the conductivity and linear dichroism are set by the helix wave vector. Moreover, the optical anisotropy exhibits two distinct frequency regimes separated by a crossover: at low frequencies the absorption axis is locked to crystal axes, while at high frequencies it tracks the helix. Our results identify polarization-resolved optics and anisotropic transport as direct probes of textured altermagnetic states and suggest a simple route to direction-selective electronic and optical functionality in altermagnets.