Strongly correlated and strongly coupled s-wave superconductivity of the high entropy alloy Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 compound

Abstract

High entropy alloy (HEA) is a random mixture of multiple elements stabilized by high mixing entropy. We synthesized a Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 bulk HEA compound as a body-centered cubic structure with lattice parameter a = 3.38 angstrom based on arc melting. From the electronic and magnetic property measurements, we obtained the superconducting properties such as electron-phonon coupling constant lambda(el-ph), electron-phonon potential Vel-ph, density of states at the Fermi level D(E-F), superconducting energy gap 2 Delta(0)/k(B)T(c), upper-critical field H-c2(0), coherence length and critical current density J(c). The compound showed a superconducting transition at T-c = 7.85 K. The compound has relatively sizeable specific heat jump (Delta C/gamma T-c), high effective mass of carrier (29 m(e)), and high Kadowaki-Woods ratio (A/gamma(2), which plays an important role in the heavy Fermi compounds), indicating that it resides within the strongly coupled s-wave superconductor within a dirty limit. Its vortex pinning force is described by the Dew-Huges double exponential pinning model, implying that there are two types of pinning mechanisms. The possible coexistence of strongly correlated behavior in s-wave superconductivity in HEA compounds is noteworthy because many of the strongly correlated superconductors, such as heavy-fermion and high T-c cuprate superconductors, have nodal gap symmetry. The HEA compound suggests exploiting different types of superconductivity with the current strongly correlated superconductors as well as metallic superconductors. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.