Superconductivity of Bi-III phase of elemental Bismuth: insights from Muon-Spin Rotation and Density Functional Theory

TL;DR

This study investigates the superconducting properties of the Bi-III phase of elemental Bismuth under pressure, revealing strong coupling superconductivity with unique magnetic and electronic characteristics supported by experimental and theoretical analyses.

Contribution

It provides new insights into the superconducting behavior of Bi-III, combining muon-spin rotation measurements with density functional theory to explore its pairing mechanisms and physical parameters.

Findings

Bi-III has the highest $ ext{κ}$ among single element superconductors.

Superconductivity in Bi-III exhibits strong coupling with $2 ext{Δ}/k_{ m B}T_{ m c} hickapprox4.34$.

Possible alternative pairing mechanisms include Fermi surface nesting.

Abstract

Using muon-spin rotation the pressure-induced superconductivity in the Bi-III phase of elemental Bismuth (transition temperature $T_{\rm c}\simeq7.05$ K) was investigated. The Ginzburg-Landau parameter $\kappa=\lambda/\xi=30(6)$ ($\lambda$ is the magnetic penetration depth, $\xi$ is the coherence length) was estimated which is the highest among single element superconductors. The temperature dependence of the superconducting energy gap [$\Delta(T)$] reconstructed from $\lambda^{-2}(T)$ deviates from the weak-coupled BCS prediction. The coupling strength $2\Delta/k_{\rm B}T_{\rm c}\simeq 4.34$ 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 the characteristic phonon frequency $\omega_{\rm ln}\simeq 5.5$ meV. An alternative pairing mechanism to the electron-phonon coupling involves the possibility of Cooper pairing induced by the Fermi surface nesting.