  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.
