Orbital Kerr effect and terahertz detection via the nonlinear Hall effect

The optical Kerr effect, widely used for probing magnetic domains, can be used to detect nonequilibrium orbital accumulation, even in the absence of spin-orbit coupling. In certain low-symmetry crystals, this orbital accumulation is associated with a nonlinear Hall effect that can be exploited for terahertz (THz) detection. As a result, the ``orbital'' Kerr effect is directly related to the THz responsivity of the material. Using first-principles calculations, the authors demonstrate here that this effect in low-symmetry crystals and multilayers can be remarkably large.