Sign control of photocurrents by spin-group-symmetry breaking in altermagnetic insulators

TL;DR

This paper explores how spin-group-symmetry breaking influences nonlinear optical responses in altermagnetic insulators, demonstrating control of photocurrents via strain and revealing a new mechanism involving spin-gap asymmetry.

Contribution

It introduces a symmetry-guided mechanism for controlling photocurrents in altermagnetic insulators using strain, supported by density functional theory calculations.

Findings

Photocurrent components are locked to strain direction.

Spin-gap asymmetry couples with N9el order and strain.

Density functional theory confirms the proposed mechanism.

Abstract

Controlling physical responses through symmetry breaking is a central paradigm in quantum materials, enabling novel functionalities. Here we determine the effects of spin-group-symmetry breaking on nonlinear optical responses of collinear altermagnetic insulators. Using shear strain as an example, we show that the direction of symmetry-breaking induced components of charge and spin photocurrents are locked to the sign of the strain. In the absence of spin-orbit coupling, this effect is intuitively captured by the spin-gap asymmetry--an imbalance between spin-up and spin-down direct band gaps which couples trilinearly with the N\'eel order and the strain. We demonstrate this mechanism with density functional theory calculations on the recently proposed altermagnet CuWP$_2$S$_6$. Having symmetry-guided control of both charge and spin photocurrents allows, vice versa, to reveal and investigate altermagnetism in insulating materials by exploration of their optical responses.