Effect of proximity of a normal layer on the anisotropy of the superconducting energy gap

To investigate the effect of a normal layer in close contact with an anisotropic superconductor on the observable anisotropy a simplified description of gap anisotropy in terms of a two-band model is used. Within McMillan's tunneling model of the proximity effect, tunneling into the normal layer provides a mechanosm for interband scattering, which serves to smear the gap structure. It is suggested that this mechanism is responsible for the failure to observe gap anisotropy in tunneling experiments on single crystal Nb.