The switchable bulk photovoltaic effect in 2D room temperature ferroelectric CuInP 2 S 6

The bulk photovoltaic effect (BPVE) is a crucial branch of nonlinear optics that plays a significant role in fundamental physics and practical applications. In this study, we have investigated the BPVE of a room-temperature ferroelectric material CuInP 2 S 6 (CIPS) through first-principles calculations and nonlinear response theory. It is revealed that there are significant differences in nonlinear photo-responsivity among the ferroelectric, paraelectric, and antiferroelectric phases under monochromatic light. We find that the nonlinear photocurrent can be switched by the chirality of the incident light, depending on the structural symmetry. Using the CI-NEB method, we have studied the evolution of photocurrent during phase transition processes such as polarization reversal and polar-to-nonpolar transitions. We observe that the reversal of ferroelectric ordering can induce a photocurrent flip, attributed to the sign change of topological physical quantities such as the shift vector and Berry curvature. Furthermore, we predict the modulation of photocurrent through chalcogen element substitution and strain engineering. Our study provides an insight into the nonlinear optics of ferroelectric materials and crucial theoretical guidance for the design of optoelectronic and photonic devices.