Disorder-induced decoupling of pancake vortices in a layered superconductor

We consider the effect of pancake vortices induced by a magnetic field on the Josephson coupling in a disordered, layered superconductor. Due to the random displacements of vortices, the magnetic field suppresses the Josephson coupling. We find the characteristic value of the ''decoupling'' field. The effective Josephson energy does not drop to zero above this field, but saturates at some small value and remains field independent in the regime of individual pinning. Crossover to the collective pinning regime at higher fields and temperatures leads to partial restoration of the Josephson energy. We studied also the influence of the pancake wandering on the field distribution inside the superconductor. We found that the feature which is most sensitive to the pancake misalignment is the large field tail in the distribution function. We show that the asymmetry of the field distribution induced by this tail disappears at fields substantially smaller than the decoupling field.