DRIVING AND PINNING FORCES ACTING ON VORTICES IN LAYERED SUPERCONDUCTORS

The vortex structure and the distribution of the transport current in a layered superconductor consisting of an alternate stack of strongly and weakly superconducting layers are theoretically studied within the framework of the Ginzburg-Landau theory. It is assumed that in the superconductor the coherence length is comparable to the layer thickness and the penetration depth is much longer than the thickness. The present theory predicts that the superconducting current mainly flows in the strongly superconducting layer, while the vortex center lies in the weakly superconducting layer. As a result the driving force acting on the vortex becomes extremely weak, since the small current density in the weakly superconducting layer is responsible for the force. Some behavior of the critical current in the cuprate superconductors YBa2Cu3O7-delta and Bi2Sr2CaCu2O8+delta may be explained with the present theory.