Known since ancient times, elemental Bismuth is a brittle metal, among the most well-characterized materials available. At ambient pressure it becomes superconducting at extremely low temperature of 0.5 mK which makes it extremely difficult to study.
The situation changes radically under pressure. Upon pressure-induced structural transition, the superconducting temperature rises to several Kelvin. Our recent muon work investigates these superconducting phases. At the intermediate pressures, the superconducting phase expels the applied magnetic field showing very clear Meissner effect, whereas the high-pressure phase allows penetration of magnetic field and forms vortices throughout the sample, which can be picked up by the implanted muons. These observations are textbook-like example of the different behavior of the Type-I and Type-II superconductors and the transformation between the two.
Find more on the two different phases in the papers:
Bi-II phase: Phys. Rev. B 99, 174506
Bi-III phase: Phys. Rev. B 98, 140504(R)