Theory for the upper critical field in superconducting multilayers with interface irregularities

The upper critical field in superconducting multilayers, which are composed of two kinds of superconducting layers with different diffusion constants and contain interface irregularities, investigated in the direction parallel to the layers. The interface irregularities enhance the upper critical field. The crossover temperature at which the superconducting nucleation position moves from one layer to another is increased as the effect of the irregularities becomes strong. As a result, the two-dimensional region where the nucleation position of the superconducting order is inside a layer with the larger diffusion constant is greatly reduced by the irregularities.