THE LOCK-IN TRANSITION OF VORTICES IN LAYERED SUPERCONDUCTORS

A review of the theory of the lock-in transition of vortices onto the layer direction in type II layered superconductors is presented. This phenomenon originates from the lowering of free energy when vortex cores are centered between adjacent layers. The approaches for the low-temperature ''quasi-2D'' as well as the 3D anisotropic regimes are reviewed. fil particular, the temperature variation of the core energy modulation is obtained by a variational method. The phenomenological model with a modulated vortex core is shown to work in all the temperature range. The behaviour of the reversible torque is described as a function of the various parameters: field, temperature, anisotropy, and the existence of the London maximum is discussed. A simple interpretation of the transition is given as well as the influence of demagnetizing fields.