Crystal symmetry selected pure spin photocurrent in altermagnetic insulators

Spin current generation in altermagnets is a central focus in spintronics. While the time-reversal-odd spin Hall effect is significant in metallic systems, insulating behavior is more common in antiferromagnets. Here, the authors demonstrate that pure spin currents can be generated in altermagnetic insulators through nonlinear photogalvanic effects, specifically via shift and injection currents. Remarkably, these mechanisms remain effective in producing directional pure spin currents even with spin-orbit coupling, in contrast to previous findings in nonmagnetic and parity-time symmetric antiferromagnetic materials.