Effect of geometrical symmetry on the angular dependence of the critical magnetic field in superconductorormal metal multilayers

摘要

The angular dependence of the upper critical field, H_c(Θ), for Nb/Pd multilayers with different geometrical symmetries (i.e., with an even or an odd number of bilayers, N_(bil)) 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 N_(bil) has a larger value of Θ~*(T) with respect to the sample with even N_(bil). The experimental results have been qualitatively explained in the framework of the Ginzburg-Landau theory. It was shown that the main features of the H_c(Θ) dependences in samples with even and odd N_(bil) values are related to the different localizations of the superconducting order parameter.