Thermodynamic and other properties of the superconductors BaPb 0.7Bi 0.3O 3 and Ba 0.7K 0.3BiO 3

Abstract

Results of a thermodynamic analysis are presented for the superconductors BaPb 0.7Bi 0.3O 3 and Ba 0.7K 0.3BiO 3. The physical quantities are calculated by numerical solutions of the Eliashberg gap equations with the electron-phonon spectra α 2( ω) F( ω) as calculated by Shirai et al., using a realistic electronic band-structure determined by the tight-binding approximation. For the superconductor BaPb 0.7Bi 0.3O 3, several models of the α 2( ω) F( ω) were studied looking for a better agreement with experimental data. The best fit is achieved with a simple constant scaling ( C = 1.25) of the Shirai's spectra. We also calculated the functional derivatives for the critical temperature T c, the critical magnetic field H c(0), and the deviation function D( t) with respect to changes in α 2( ω) F( ω).