Intrinsic Dynamic Generation of Spin Polarization by Time-Varying Electric Field

Electric control of spin in insulators is desired for low-consumption and ultrafast spintronics, but the underlying mechanism remains largely unexplored. Here, we propose an intrinsic effect of dynamic spin generation driven by time-varying electric field. In the intraband response regime, it can be nicely formulated as a Berry curvature effect and leads to two phenomena that are forbidden in the dc limit: linear spin generation in nonmagnetic insulators and intrinsic Néel spin-orbit torque in PT-symmetric antiferromagnetic insulators. These phenomena are driven by the time derivative of field rather than the field itself, and have a quantum origin in the first-order dynamic anomalous spin polarizability. Combined with first-principles calculations, we predict sizable effects driven by the terahertz field in nonmagnetic monolayer Bi and in antiferromagnetic even-layer MnBi_{2}Te_{4}, which can be detected in experiment.