BEYOND THE SIMPLE HEXAGONAL ABRIKOSOV VORTEX LATTICE IN LAYERED SUPERCONDUCTORS

In layered superconductors as high-T-c materials but also organic supe rconductors, chalcogenides and superlattices, the simple concept of an distorted hexagonal lattice of straight vortices becomes unsufficient . Due to anisotropy and short coherence lengths, quite new vortex stru ctures may arise. Some of them, as staircase vortices, simply add a mo dulation in the direction of vortex lines. This phenomenon is reviewed , together with the resulting lock-in transition, especially when the effects of the layered structure are weak. More exotic structures like a decomposed vortex lattice can also occur in specific situations: th ey involve two perpendicular sublattices, one parallel and one normal to the layers. We propose that extended defects as twin boundaries or irradiation tracks can trigger such a structure even in moderately ani sotropic compounds as Y:123.