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 film. As a matter of fact, the single-crystal PbS is a rock-salt crystal structure, which is centrosymmetric. However, the structural inversion symmetry breaking in the surface of PbS pronounced the Rashba splitting at M-point of Brillouin zone due to spin-orbit coupling. The electron spin and momentum are tightly locked, and thus the spin current can be effectively converted into charge current under circularly polarized light excitation. Consequently, an obvious circular photogalvanic effect voltage was observed in the Rashba-type spin orbit interaction system, which is identified by the electrical measurements on the circular photogalvanic effect among the PbS thin film. This work demonstrates the feasibility of achieving strong spin-orbit coupling in centrosymmetric materials, providing a compelling material platform for the developing of low-cost spintronic devices.