# On the superconducting nature of the Bi-II phase of elemental Bismuth

## TL;DR

This study combines experimental muon-spin rotation measurements and theoretical Eliashberg calculations to confirm that the Bi-II phase of Bismuth is an intermediately-coupled type-I superconductor with a transition temperature around 3.92 K.

## Contribution

It provides the first combined experimental and theoretical analysis confirming the superconducting nature and properties of the Bi-II phase of Bismuth.

## Key findings

- Bi-II is a type-I superconductor with $T_c \,\approx 3.92$ K.
- Experimental and theoretical results agree on the critical field and transition temperature.
- Bi-II exhibits intermediate electron-phonon coupling strength.

## Abstract

The superconductivity in the Bi-II phase of elemental Bismuth (transition temperature $T_{\rm c}\simeq3.92$ K at pressure $p\simeq 2.80$ GPa) was studied experimentally by means of the muon-spin rotation as well as theoretically by using the Eliashberg theory in combination with Density Functional Theory calculations. Experiments reveal that Bi-II is a type-I superconductor with a zero temperature value of the thermodynamic critical field $B_{\rm c}(0)\simeq31.97$~mT. The Eliashberg theory approach provides a good agreement with the experimental $T_{\rm c}$ and the temperature evolution of $B_{\rm c}$. The estimated value for the retardation (coupling) parameter $k_{\rm B}T_{\rm c}/\omega_{\rm ln} \approx 0.07$ ($\omega_{\rm ln}$ is the logarithmically averaged phonon frequency) suggests that Bi-II is an intermediately-coupled superconductor.