Coexisting Rashba/Dresselhaus Spin Splitting in Solution‐Processed Bournonite Films Using Circular Photogalvanic Effect

Abstract Spin‐split electronic states, such as the Rashba and Dresselhaus effects, are central to the development of energy‐efficient spintronic applications, enabling the manipulation of spin information without applying magnetic fields. While validating spin‐split electronic states typically requires sophisticated angle‐resolved photoemission spectroscopy under stringent sample preparation conditions, the circular photogalvanic effect (CPGE)— which measures helicity‐dependent photocurrent at zero bias—offers a sensitive, nondestructive, and accessible benchtop technique for probing such spin‐splitting in solids. Bournonite (CuPbSbS 3 ) is a non‐centrosymmetric semiconductor that offers several advantages including Earth‐abundant constituents, thermodynamic stability, and compatibility with solution‐based thin‐film fabrication techniques. Bournonite has been theoretically predicted to host robust spin‐split states due to its intrinsic broken bulk inversion symmetry, yet no experimental confirmation has been reported to date. Here, both transverse and longitudinal CPGE responses are measured in solution‐processed thin films of bournonite, providing direct support for coexisting Rashba and Dresselhaus spin‐split states in this material due to structural and bulk inversion asymmetry, as corroborated with first‐principles calculations. The results not only contribute to understanding this material's spintronic potential and its tunable, energy‐resolved spin structure, but also demonstrate the utilization of CPGE to identify spin‐orbit‐driven phenomena across a wide variety of non‐centrosymmetric semiconductors.