Crystal Symmetry Selected Pure Spin Photocurrent in Altermagnetic Insulators

TL;DR

This paper demonstrates that altermagnetic insulators can generate pure spin photocurrents protected by symmetry, with potential applications in spintronics, supported by first-principles calculations on specific materials.

Contribution

It reveals symmetry-protected pure spin photocurrents in altermagnets and uncovers a linear-inject-current mechanism in BiFeO3, advancing understanding of spin photocurrents in insulators.

Findings

Spin and charge photocurrents are symmetry-protected in altermagnets.

Pure spin current can exist without charge current along specific directions.

The linear-inject-current mechanism in BiFeO3 explains enhanced photovoltaic effects.

Abstract

The generation of time-reversal-odd spin-current in metallic altermagnets has attracted considerable interest in spintronics. However, producing pure spin-current in insulating materials remains both challenging and desirable, as insulating states are frequently found in antiferromagnets. Nonlinear photogalvanic effects offer a promising method for generating spin-current in insulators. We here revealed that spin and charge photocurrents in altermagnets are protected by spin point group symmetry. Unlike the photocurrents in parity-time symmetric materials, where spin-orbit coupling (SOC) induces a significant charge current, the spin-current in altermagnets can exist as a pure spin current along specific crystal directions regardless of SOC. We applied our predictions using first-principles calculations to several distinct materials, including wurtzite MnTe and multiferroic BiFeO3. Additionally, we elucidated the previously overlooked linear-inject-current mechanism in BiFeO3 induced by SOC, which may account for the enhanced bulk photovotaic effect in multiferroics.