Superconducting ground state and electronic properties of σ-Phase Ta–W–Mo-Re-Os high entropy alloys

We report on a new member of superconducting high entropy alloys, Ta₇W_10+xMo_30-xRe₃₃Os₂₀, 0≤x ≤ 12 (σ-phase), which was synthesized and its superconducting properties were investigated. It was found that bulk superconductivity with a maximum T_c of 5.9 K observed at x = 0. The superconducting T_c decreases with the increase of x, which is directly associated with a reduction in electron-phonon interactions. At low temperatures, the specific heat demonstrates the presence of conventional, fully gapped superconductivity with weak coupling. The collective pinning of vortices is more dominant because point defects play a significant role, as observed from the thermally activated flux flow behaviour. The electronic parameters in these compounds fall within a conventional range on the Uemura plot, suggesting that σ-phase high entropy alloys have a conventional superconducting ground state.