Spin relaxation and transport behaviors in altermagnetic systems

Abstract: The D'yakonov-Perel' (DP) spin-relaxation mechanism has traditionally been associated with either relativistic spin-orbit coupling, which breaks space-inversion symmetry, or inhomogeneous magnetization, which breaks both time-reversal and translational symmetries. Here, we investigate spin relaxation mechanism in altermagnetic systems which possess novel magnetic states characterized by sublattices connected through crystal-rotation symmetries and opposite spins with zero overall net magnetization and absence of spin-orbit coupling. We find that altermagnetic states exhibit DP-type spin relaxations in both strong- and weak-scattering regimes, with the spin relaxation rate decreasing to zero as the temperature approaches the critical temperature of the altermagnetic phase transition. However, the scattering time involved in this spin relaxation mechanism is not the momentum relaxation time, in contrast to the conventional DP spin relaxation. Using a kinetic approach incorporating rigorous microscopic scattering, we demonstrate that the spin Hall current is highly anisotropic and proportional to the degree of altermagnetic order.