Light-induced nonlinear Edelstein effect under ferroaxial ordering

Ferroaxial ordering, a spontaneous rotational distortion of the atomic arrangement, brings about a cross-product-type spin-orbit coupling (SOC) manifested as an electric toroidal dipole. We propose the light-induced nonlinear Edelstein effect (NLEE) -- a second-order optical response in which a static magnetization is induced by a time-dependent electric field -- as a promising probe of ferroaxial ordering. First, we elucidate the relationship between the NLEE tensor and the electric toroidal dipole. By decomposing the polarization modes of light, we find that both the linearly polarized and circularly polarized light couple to the electric toroidal dipole via distinct mechanisms. We then demonstrate the NLEE using a minimal model that incorporates ferroaxial ordering. Our analysis reveals that effective coupling between orbital magnetization and SOC induces spin magnetization. In particular, the spin magnetization is tilted owing to the electric toroidal dipole; the tilt angle reflects the ratio between the ferroaxial-origin SOC and the relativistic SOC.