The critical temperature of a superconductor on a possible mediated pairing mechanism

Abstract

The possibility of pairing correlations arising from the quenching of the repulsiveelectron–ion Darwin term in the pairon (Cooper pair) state is examined. Twopairing processes, arising from ionic density fluctuations (phonons) and fromelectronic density fluctuations (excitons), are shown to dominate in lowTc andhigh Tc superconductors, respectively. Based on a two-body interaction potential the BCS type of wavefunction and reduced Hamiltonian are obtained. Asquenching occurs only when a pairon is scattered by the nucleus without recoil between an electronand a hole section of the Fermi surface, a two-band model with umklapp processes gives theTc equation for both the phonon- and exciton-coupled superconductors whose solution issimilar to that obtained by Eliashberg equations except that the dependence ofTc on structure is explicitly included.