MAGNETIC-FLUX PENETRATION INTO JOSEPHSON NETWORKS IN A CRITICAL STATE

A theory of magnetic field penetration in a critical state is derived for Josephson networks (i.e., for granular superconductors) when magnetic fields thread through intergranular Josephson junction regions rather than through grains. In the framework of a microscopic approach we find the critical current J(c)(B) as a function of magnetic induction B and the magnetic field profiles, which in some special cases are described by the well-known phenomenological theories of Bean and Kim and Anderson. In some cases J(c)(B) has an oscillating character that relates to a step structure of B(x). 2D Josephson networks are studied. We find that the profile of a magnetic field threading through a Josephson network can be no steeper than that described by the Kim-Anderson model.