Superconductivity of Bi-III phase of elemental bismuth: Insights from muon-spin rotation and density functional theory

Abstract

Using muon-spin rotation the pressure-induced superconductivity in the Bi-III phase of elemental bismuth (transition temperature Tc≃7.05 K) was investigated. A Ginzburg-Landau parameter κ=λ/ξ=30(6) (λ is the magnetic penetration depth, ξ is the coherence length) was estimated, which turns out to be the highest among known single element superconductors. The temperature dependence of the superconducting energy gap [Δ(T)] reconstructed from λ-2(T) deviates from the weakly coupled BCS prediction. The coupling strength 2Δ/kBTc≃4.34 was estimated, thus implying that Bi-III stays within the strong-coupling regime. The density functional theory calculations suggest that superconductivity in Bi-III could be described within the Eliashberg approach with a characteristic phonon frequency ωln≃5.5 meV. An alternative pairing mechanism to the electron-phonon coupling involves the possibility of Cooper pairing induced by Fermi-surface nesting.