Critical fields of superconducting sandwiches SIS

The temperature and angular dependences of the critical magnetic field are studied for V/Si/V sandwiches formed by two identical metal layers separated by a semiconductor layer, as well as for various types of asymmetric sandwiches having different parameters of two superconducting plates. It is found that all thin-film sandwiches in a parallel magnetic field display a phenomenon such as dimensional crossover associated with a transition between two different two-dimensional states. The presence of such a crossover, which points towards a change in the localization of a superconducting nucleus, is confirmed by the results of measurements of angular dependence of the critical field. Differences in crossover mechanisms are discussed for symmetric and asymmetric sandwiches, as well as the peculiarities connected with the formation of a one-dimensional mixed state in the sandwich layers.

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