Effects of equivalent composition on superconducting properties of high-entropy REOBiS2 (RE = La, Ce, Pr, Nd, Sm, Gd) single crystals

Abstract

Superconductors are influenced by high-entropy alloys (HEAs); these have been investigated in various functional materials. REOBiS2 (RE = La, Ce, Pr, Nd, Sm, and Gd in different combinations) single crystals with HEAs at the RE-site were successfully grown using the flux method. The obtained crystals were plate-shaped (∼1 mm2) with a well-developed c-plane. Ce was present in both trivalent (Ce3+) and tetravalent (Ce4+) electronic configurations; the concentration of Ce4+ at the RE-site was approximately 10 at% in all single crystals. The single crystals showed superconducting transition temperature with zero resistivity within 1.2–4.2 K. The superconducting transition temperature, superconducting anisotropy, electronic specific heat coefficient, and Debye temperature of the crystals were not correlated with the mixed entropy at the RE-site. Except for the electronic specific heat coefficient, the variation of these parameters as a function of mixed entropy showed different trends for equivalent and non-equivalent RE element compositions. Thus, the configuration of RE elements influences the superconducting properties of REOBiS2 single crystals, alluding to a method of modulating transition temperatures.