Growth and Characterization of ROBiS₂ High-Entropy Superconducting Single Crystals

A series of high-entropy superconductors, ROBiS₂ (R = La + Ce + Pr + Nd + Sm), have been successfully grown in the form of single crystals using CsCl flux. The obtained single crystals have a platelike shape with a size of 0.5-2.0 mm and a thickness of 70-450 μm, and they are cleavable along the c-plane. The c-axis lattice constants of the obtained ROBiS₂ single crystals have similar values of 13.47-13.57 Å. The Ce in the obtained ROBiS₂ single crystals was in a mixed-valence state, comprising both Ce³⁺ and Ce⁴⁺. On the other hand, Pr and Sm showed only the trivalent state. The superconducting transition temperatures of ROBiS₂ single crystals were approximately 2-4 K. The superconducting transition temperature and superconducting anisotropies of R-site mixed high-entropy samples increased with a decrease in the mean ionic radius of the R-site. Moreover, a deviation in the tendency to exhibit superconducting properties was observed based on the difference in the R-site mixed entropy. R-site mixed entropy in ROBiS₂ superconductors may affect their superconducting properties.