Strongly Correlated and Strong Coupled S-Wave Superconductivity of the High Entropy Alloy Ta _1/6Nb _2/6Hf _1/6Zr _1/6Ti _1/6 Compound

Abstract

High entropy alloy (HEA) is a random mixture of multiple elements stabilized by a high mixing entropy. We synthesized Ta_1/6Nb_2/6Hf_1/6Zr_1/6Ti_1/6 bulk HEA compound as a body-centered cubic structure with the lattice parameter a = 3.38 Å by arc melting. From the electronic and magnetic properties measurements, we found that it exhibits a superconducting transition at T_c = 7.85 K. From the superconducting properties such as electron-phonon coupling constant λ_el-ph, electron-phonon potential V_el-ph, density of states at the Fermi level D(E_F), superconducting energy gap 2Δ(0)/k_BT_c, upper-critical field H_c2(0), coherence length ξ, and critical current Jc etc, we found that it is a strong coupled s-wave superconductor in a dirty limit. Meanwhile, the relative sizeable specific heat jump (ΔC/γT_c), high effective mass of carrier (29 m_e), and high Kadowaki-Woods ratio which is close to one of heavy Fermi compounds indicate that it resides in the limit of a strongly correlated system. The vortex pinning force is described by the Dew-Huges double exponential pinning model, implying that there are two types of pinning mechanism. The possible coexistence of strongly correlated behavior in s-wave superconductivity on the HEA compounds is noteworthy because many of the strongly correlated superconductors have a nodal gap symmetry such as heavy fermion and high Tc cuprate superconductors. The HEA compound suggests a different types of superconductivity with the current strongly correlated superconductors as well as metallic superconductors.

Keywords: Superconductor, High entropy alloy, s-wave, strongly correlated system