Effects of equivalent composition on superconducting properties of high-entropy REOBiS${}_2$ (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. REOBiS${}_2$ (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 mm${}^2$) with a well-developed c-plane. Ce was present in both trivalent (Ce${}^{3+}$) and tetravalent (Ce${}^{4+}$) electronic configurations; the concentration of Ce${}^{4+}$ 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 REOBiS${}_2$ single crystals, alluding to a method of modulating transition temperatures.

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