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 A based on arc melting. From the electronic and magnetic property measurements, we obtained the superconducting properties such as electron-phonon coupling constant λel-ph, electron-phonon potential Vel-ph, density of states at the Fermi level D(EF), superconducting energy gap 2Δ(0)/kBTc, upper-critical field Hc2(0), coherence length ξ, and critical current density Jc. The compound showed a superconducting transition at Tc = 7.85 K. The compound has relatively sizeable specific heat jump (ΔC/γTc), high effective mass of carrier (29 me), and high Kadowaki-Woods ratio (A/γ2, 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 Tc 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.