JOSEPHSON-COUPLED SYSTEMS IN PERPENDICULAR MAGNETIC-FIELDS

We calculate the critical current along the c axis of a stack of Josephson-coupled layers when the applied magnetic field is perpendicular to the junctions plane. The anisotropy parameter and the Josephson interlayer critical current in the Lawrence-Doniach model are renormalized by the vortex fluctuations and have to be determined self-consistently. This leads to the existence of a decoupling phase transition in the (H, T) plane. The decoupling phase transition is first order for moderate (bare) anisotropies and second order for large anisotropies. We consider the effect of pinning centers and show that only strong disorder affects the critical current. Application of the formalism to single crystals, tapes, and films of highly anisotropic, layered superconductors is discussed. The magnetic field and temperature dependence of the critical current in tapes is calculated for the brick-wall model.