Giant Rashba spin splitting for circular photogalvanic effect in wafer-scale lead sulfide thin film

The spin degree of freedom of charge carriers provides an effective way to expand the functionality of conventional electronic devices. In this work, based on density functional theory, we discover giant Rashba-type spin splitting with a remarkable Rashba coefficient of 2.85 eV Å in wafer-scale lead sulfide (PbS) thin films. As a matter of fact, single-crystal PbS has a rock salt crystal structure, which is centrosymmetric. However, structural inversion symmetry breaking at the surface of PbS enhances Rashba splitting at the M-point of the Brillouin zone due to spin–orbit coupling. The electron spin and momentum are tightly locked, thus the spin current can be effectively converted into charge current under circularly polarized light excitation. Consequently, an obvious circular photogalvanic effect (CPGE) voltage was observed in the Rashba-type spin–orbit interaction system, as identified by electrical measurements of the CPGE in PbS thin films. This work demonstrates the feasibility of achieving strong spin–orbit coupling in centrosymmetric materials, providing a compelling platform for developing low-cost spintronic devices.