Effect of geometrical symmetry on the angular dependence of the critical magnetic field in superconductor/normal metal multilayers

Abstract

The angular dependence of the upper critical field, Hc (Θ), for Nb/Pd multilayers with different geometrical symmetries (i.e., with an even or an odd number of bilayers, Nbil) and thickness of Nb and Pd layers of the order of superconducting coherence length were investigated (the angle Θ is here defined from the plane parallel to the sample surface). The presence of an angular dimensional crossover at some temperature dependent angle Θ* (T) was established. At angles Θ< Θ* (T) the multilayers are in two-dimensional mode while at Θ> Θ* (T) they are in a three-dimensional one. In addition, the sample with odd Nbil has a larger value of Θ* (T) with respect to the sample with even Nbil. The experimental results have been qualitatively explained in the framework of the Ginzburg-Landau theory. It was shown that the main features of the Hc (Θ) dependences in samples with even and odd Nbil values are related to the different localizations of the superconducting order parameter. © 2005 The American Physical Society.