Parallel field penetration in a layered superconductor

Abstract

The Bean-Livingston entrance field H s for vortex penetration at the surface is calculated for layered superconductors with Josephson interlayer coupling and field parallel to the layers. Two regimes must be distinguished: close to T c, one can use the anisotropic London theory, so H s is of the order of H c, the thermodynamic critical field, and is the same as for a field normal to the layers. On the opposite, when the transverse coherence length ξ c is smaller than the interlayer distance d, H s becomes smaller than H c and is of the order of ( ξ c d )H c . Contrary to the entrance field for pure Josephson vortices (fluxons) in junctions, this field is still much larger than the first critical field H c1∥. This behaviour is a consequence of the specific structure of the vortex core in a layered superconductor and results in a crossover from a linear to a square root temperature dependence as the temperature is lowered.