Helicity-Controlled Spin Hall Angle in 2D Altermagnets with Rashba Spin-Orbit Coupling

We investigated the efficiency of charge-to-spin conversion in two-dimensional Rashba altermagnets, a class of materials that combines the characteristics of both ferromagnets and antiferromagnets. Using quantum linear response theory, we quantified the longitudinal and spin Hall conductivities in this system and demonstrated a substantial enhancement in the spin Hall angle below the band crossing point through the dual effects of relativistic spin–orbit interaction and nonrelativistic altermagnetic exchange interaction. Additionally, the results showed that the skew scattering and intrinsic mechanisms arising from Fermi sea states are almost negligible in this system, in contrast to conventional ferromagnetic Rashba systems. Our findings not only elucidate the spin dynamics in Rashba altermagnets but also pave the way for developing novel strategies for manipulating charge-to-spin conversion via sophisticated control of noncollinear and collinear out-of-plane spin textures.