PT-Symmetry-Enabled Spin Circular Photogalvanic Effect in Antiferromagnetic Insulators

The short timescale spin dynamics in antiferromagnets is an attractive feature from the standpoint of ultrafast spintronics. Yet generating highly polarized spin current at room temperature remains a fundamental challenge for antiferromagnets. We propose a spin circular photogalvanic effect (spin CPGE), in which circularly polarized light can produce a highly spin-polarized current at room temperature, through an "injection-current-like" mechanism in parity-time (PT)-symmetric antiferromagnetic (AFM) insulators. We demonstrate this effect by first-principles simulations of bilayer CrI3 and room-temperature-AFM hematite. The spin CPGE is significant, and the magnitude of spin photocurrent is comparable with the widely observed charge photocurrent in ferroelectric materials. Interestingly, this spin photocurrent is not sensitive to spin-orbit interactions, which were regarded as fundamental mechanisms for generating spin current. Given the fast response of light-matter interactions, large energy scale, and insensitivity to spin-orbit interactions, our work gives hope to realizing fast-dynamic and temperature-robust pure spin current in a wide range of PT-symmetric AFM materials, including topological axion insulators and weak-relativistic magnetic insulators.