Tunable Odd-Parity Spin Splittings in Altermagnets

TL;DR

This paper introduces a theoretical framework to induce and control odd-parity spin splittings in collinear altermagnets using light or loop-current order, enabling new spintronics functionalities.

Contribution

It develops mechanisms to generate and manipulate odd-parity spin textures in altermagnets via two-color light fields and P-odd loop-current coupling, expanding spintronics control.

Findings

Proper phase-locked two-color driving induces a static P,T=-,- order.

Coupling to P-odd loop-current order produces controllable mixed-parity spin textures.

Application to PT-symmetric magnets yields a nonrelativistic dissipationless spin Hall effect.

Abstract

Momentum-dependent spin splitting and its relation to inversion ($P$) and time-reversal ($T$) symmetries are central to nonrelativistic spintronics. Representative examples include collinear altermagnets with $(P,T)=(+,-)$ and non-collinear odd-parity magnets with $(P,T)=(-,+)$. In this work, we develop a theoretical framework to induce odd-parity spin splittings in the more abundant collinear altermagnets through two mechanisms: driving by a two-color linearly polarized light field or coupling to a $P$-odd loop-current order. Properly phase-locked two-color driving induces a static $(P,T)=(-,-)$ order, symmetry-equivalent to a translationally invariant $P$-odd loop-current order. Coupling this order to an altermagnet produces a controllable mixed-parity spin texture, opening new avenues for the electrical and optical manipulation of spin-polarized currents in spintronics applications. The same mechanism applied to a collinear $PT$-symmetric magnet induces a distinct $(P,T)=(+,+)$ state with a nonrelativistic dissipationless anomalous spin Hall conductivity. We present group-theory and microscopic Floquet theory to highlight the emergent responses.