  The short timescale spin dynamics in antiferromagnets is an attractive
feature from the standpoint of ultrafast spintronics. Yet generating highly
polarized spin currents 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 spin current without net
charge 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. Our calculations show that the spin-CPGE is
significant, and the magnitude of spin photo-current 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 a fast-dynamic and
temperature-robust pure spin current in a wide range of PT-symmetric AFM
materials, including weak-relativistic magnetic insulators and topological
axion insulators.
