At ambient pressure, bulk rhombohedral bismuth is a semimetal. In a semimetal the concentration of mobile electrons is extremely low. The concentration of mobile electrons in metals is with roughly one mobile electron per atom much higher. Therefore, it was thought that bulk Bi shows no superconductivity (SC).
Srinivasan Ramakrishnan and colleagues, Tata Institute of Fundamental Research (TIFR), Mumbai, India, have discovered bulk SC of a high quality single crystal of Bi (99.998 % pure) at 0.53 mK with an estimated critical field of 5.2 µTesla at 0 K and ambient pressure.
This discovery cannot be explained by the conventional Bardeen-Cooper-Schrieffer theory. The adiabatic approximation fails for Bi. The electronic (Fermi) energy is much larger than the lattice (vibration) energy used in this standard model. The researchers say that future theoretical work is necessary to understand SC in the non-adiabatic limit in systems with low-carrier density and unusual band structure, such as Bi.
- Evidence for bulk superconductivity in pure bismuth single crystals at ambient pressure,
Om Prakash, Anil Kumar, A. Thamizhavel, S. Ramakrishnan,