Non-phononic mechanism of superconductivity in pure semi-metallic Bismuth single crystal at sub-milli Kelvin

Very recently, the elusive phenomenon of superconductivity in pure semi-metallic Bismuth single crystal has been experimentally observed at extremely low transition temperature of 0.53 mK. Electrons, charged fermions, in this crystal form a very rare gas with interparticle separation of nearly 185A˚. But it is a highly quantum mechanical degenerate gas at such a low temperature with thermal de Broglie wavelength equal to a fraction of a million Angstrom. In such a dilute system the peculiar oscillatory behavior of the generalized electronic dielectric function at large distances can give rise to an attractive interaction between two electrons. The interaction of electrons therefore, can be described by a pseudo-potential with a negative scattering length that gives rise to the formation of Cooper pairs and then bulk superconductivity in the framework of BCS theory. It turns out that the value of scattering length of 3.265A˚ can explain the observed superconducting transition temperature. The complexity of ellipsoidal Fermi surfaces of Bismuth and different values of electronic mass along its three crystal axes, consistent with the symmetry of its crystal structure, have been incorporated in the analysis. It follows that there will not be any Isotope effect. The suggested theoretical argument is akin to what has been proposed recently in neutral atomic rare gas of fermions in magnetic traps to study the presence of superfluidity in these systems.