Tunable spin photogalvanic effect in two-dimensional van der Waals ferroelectric semiconductors with spin-orbit coupling

Spin photogalvanic effect is a nonlinear effect that can generate spin currents through optical excitation in intrinsic semiconductors without parity inversion symmetry. The efficient control of the spin photogalvanic effect is of great significance for the research of computing-in-memory devices. In this work, we investigate the ferroelectric modulation of the spin photogalvanic effect in two-dimensional (2D) van der Waals (vdW) ferroelectric semiconductors with spin-orbit coupling, including the in-plane, out-of-plane, and in-plane/out-of-plane-coupled ferroelectrics. We provide the general form of the spin photogalvanic effect controlled by ferroelectricity in 2D vdW spin-orbit coupling ferroelectric semiconductors by the second-order perturbation theory. In the in-plane ferroelectrics excited by circularly polarized light, we discover an effect where the reversal of the ferroelectric polarization will maintain the spin current unchanged but change the direction of the charge current. We name this effect the hidden spin current modulation. Using first-principles quantum transport simulation, we validate our theory with three cases of the black phosphorus-like Bi (in-plane ferroelectric), monolayer \ensuremath{\alpha}-GeTe (out-of-plane ferroelectric), and $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ (in-plane and out-of-plane coupled ferroelectric). Our study paves the way for the research of next-generation low-dimensional computing-in-memory devices.