Superconductivity in equimolar Nb-Re-Hf-Zr-Ti high entropy alloy

Highlights: • Detailed superconducting properties of a new high entropy alloy superconductor Nb₂₀Re₂₀Zr₂₀Hf₂₀Ti₂₀ were studied. • The material is a type-II moderately coupled single-gap BCS superconductor. • Superconducting transition temperature T_C = 5.3 K and lower critical field H_C1(0) = 33 mT. • The obtained value of the upper critical field H_C2(0) (8.88 T) is close to the Pauli limiting field. Herein, we report the synthesis and detailed superconducting properties of a new high entropy alloy superconductor with nominal composition Nb₂₀Re₂₀Zr₂₀Hf₂₀Ti₂₀ using powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), magnetization, transport, and thermodynamic measurements. The room temperature powder XRD confirms that the alloy is arranged on a simple body-centered cubic crystal lattice with lattice parameter a = 3.38 (1) Å. EDX measurement yields an average composition of Nb₂₁Re₁₆Zr₂₀Hf₂₃Ti₂₀ (in atomic $\text{\%}$). Transport, magnetic and heat capacity measurements reveal that the material is a type-II superconductor with the bulk superconducting transition at $T_c$ = 5.3 K, lower critical field $H_{c1}$ (0) = 33 mT and upper critical field $H_{c2}$(0) = 8.88 T. Low - temperature specific heat measurement indicates that the sample is a moderately coupled superconductor, and the electronic specific heat data fits well with the single-gap BCS model.