Strongly correlated and strongly coupled s-wave superconductivity of the high entropy alloy Ta_1/6Nb_2/6Hf_1/6Zr_1/6Ti_1/6 compound

High entropy alloy (HEA) is a random mixture of multiple elements stabilized by high mixing entropy. We synthesized a Ta_1/6Nb_2/6Hf_1/6Zr_1/6Ti_1/6 bulk HEA compound as a body-centered cubic structure with lattice parameter a = 3.38 Å based on arc melting. From the electronic and magnetic property measurements, we obtained 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 density J_c. The compound showed a superconducting transition at T_c = 7.85 K. The compound has relatively sizeable specific heat jump (ΔC/γT_c), high effective mass of carrier (29 m_e), 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 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.