Mechanisms of superconductivity studied by two-particle emission

It is shown theoretically that the one-photon two-electron emission spectroscopy of superconducting surfaces provides novel information on the mechanisms of superconductivity. In particular, measured angular correlations of the photo-excited (Cooper) pairs can be related to the Cooper pair wave function in momentum space. We outline how the use of circularly polarized photons gives access to phase properties of the superconducting gap function. Furthermore, we discuss the influence of the topology of the sample and the influence of an external magnetic field for the case of superconducting rings pierced by a magnetic flux.