Intrinsic Electronic Structure and Inhomogeneity of High-Entropy Layered REOBiS₂ Superconductors

Two decades after the discovery of high-entropy alloys (HEAs), the field has witnessed these systems rise as prominent examples of high-performance functional materials, overcoming established knowledge of multicomponent systems. HEA superconductors are currently under thorough investigation due to their robust superconducting state and the possibility of enhancing their figure of merit through the high-entropy approach, in addition to the well-known mechanical and thermal properties of these materials. Here, we have investigated the electronic structure of HEA-type REOBiS₂ layered superconductors (RE = rare earth) using spectromicroscopy and angle-resolved photoemission spectroscopy (ARPES) with a submicron beam size. The overall features of the fundamental electronic structure are robust, showing limited effects of mixing entropy. We find an inherent coexistence of phases driven by local fluctuations in the interlayer interactions. This coexistence exhibits distinct patterns for different samples characterized by varying configurational entropy. Similarly, the Luttinger volume estimated from the ARPES spectra reveals differing self-doping regimes, indicating that RE valence fluctuations are possibly influenced by configurational disorder. Overall, this study represents the first report on the electronic structure of HEA-type BiS₂-based superconductors and provides valuable insight into controlling superconducting properties by tailoring nano- to microstructures through a high-entropy approach.