Conductivity anisotropy and linear dichroism in spin-textured altermagnets

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.