Pairing interaction in surface superconductivity

The microscopic expressions for the superconducting parameters are derived for a surface system. The formulation fully takes surface and periodicity induced nonlocality in the electron-phonon interaction and in the Coulomb electron-electron interaction into account. Thus, in contrast to the commonly used jellium models, it is applicable to transition-metals as well as semiconductor surfaces. As an example the exciton mechanism postulated for superconductivity is discussed. It is shown that surface nonlocality, in contrast to local bulk treatments, allows for electron-exciton-electron coupling and thus can induce attractive interaction