MgB2 superconductivity properties in a two-gap model

For MgB2 where coexist two coupled superconductivity gaps a two-band scheme has been developed. Three interaction channels have been taken into account: a pair-transfer type sigma - pi-interband repulsion, a sigma-intraband effective attraction of electron-phonon nature, and a sigma-intraband Coulomb interaction. By means of simultaneous fitting of T-c specific heat jump and zero-temperature gaps ratio the optimal values of interaction constants have been found. The T-c isotope effect exponent, the temperature dependencies of gaps and the thermodynamic characteristics (specific heat, Hc(2)) calculated agree with the experimental findings. The theoretical curve of T-c vs chemical potential reproduces qualitatively the influence of doping on superconductivity phase transition in MgB2.