TITLE:
Quantum Statistical Theory of Superconductivity in MgB2
AUTHORS:
S. Fujita, A. Suzuki, Y. Takato
KEYWORDS:
Crystal Structure, BCS Hamiltonian, Electron-Phonon Interaction, Cooper Pairs, Bose-Einstein Condensation, Superconductivity
JOURNAL NAME:
Journal of Modern Physics,
Vol.7 No.12,
August
31,
2016
ABSTRACT: A quantum statistical theory of the superconductivity in MgB2 is developed regarding it as a member of the graphite intercalation compound. The superconducting temperature Tc for MgB2, C8K ≡ KC8, CaC6, are 39 K, 0.6 K, 11.5 K, respectively. The differences arise from the lattice structures. In the plane perpendicular to the c-axis, B’s form a honeycomb lattice with the nearest neighbour distance while Mg’s form a base-hexagonal lattice with the nearest neighbour distance above and below the B-plane distanced by . The more compact B-plane becomes superconducting due to the electron-phonon attraction. Starting with the generalized Bardeen- Cooper-Schrieffer (BCS) Hamiltonian and solving the generalized Cooper equation, we obtain a linear dispersion relation for moving Cooper pairs. The superconducting temperature Tc identified as the Bose-Einstein condensation temperature of the Cooper pairs in two dimensions is given by , where is the Cooper pair density, the Boltzmann constant. The lattices of KC8 and CaC6 are clearly specified.