Pairing mechanism and transition temperature of Ba-Pb-BiO superconductors

The nature of pairing mechanism in cubic perovskite BaPbBiO3 has been investigated by developing a model potential which involves electron-electron, electron-optical phonon as well as electron-plasmon interactions. The interaction potential was used to obtain the pairing parameters as coupling strength and Coulomb repulsive parameter. Coupled oscillations of electronic charge with longitudinal optical phonon describe the superconducting nature of bismuth oxides. Estimated value of coupling strength (λ=0.84) is consistent with a moderate attractive interaction. The screened Coulomb repulsive parameter (μ=0.22) infers the poor screening of charge carriers with low carrier concentration and reflects a small density of states. The superconducting transition temperature (Tc) of BaPb0.75Bi0.25O3 is evaluated as 15.5K which is consistent with the earlier reported data. The analysis has led to the conclusion that a weak to moderate coupling exists and the coupling of charge oscillations with longitudinal optical phonon mode could be a reason to the superconductivity in Ba-Pb-BiO superconductors. (author)