Theory of a fallen high Tc superconductivity in Ultra Low Tc Bismuth

Abstract

Superconductivity with an ultra low Tc  ∼  0.5 mK was discovered recently in bismuth, a semimetal. We begin with a reference cubic lattice, of a cooperatively dimerized (cubic) A7 structure of Bi and develop a model. Using an earlier observation of Jones and Peierls of a quasi one dimensionality and half filled band character of all three 6p bands, we develop a theory for solid Bi. We suggest that electron correlation effects that gets enhanced in quasi one dimensional systems has profound consequences. We show that Bi is a failed high Tc superconductor, because of a strong competition from a valence bond dimerization instability that causes a cubic to A7 distortion. A consequent gap opening leaves the experimentally seen small fermi pockets. Signatures of the fallen high Tc superconductivity in the normal state properties of Bi and how to resurrect high Tc superconductivity are discussed. It is also likely that because of an appreciable coulomb driven inter band pair scattering, PT violating chiral superconductivity is possible. Our theory is also applicable to the A7 and cubic phases of Sb, As and P, all in the same column as Bi in the periodic table.