EDGE SUPERCONDUCTING STATES

Surface superconductivity usually refers to the nucleation of supercon ctivity near the outer surface of a bulk specimen. The same intrinsic phenomena takes place in a patterned thin film giving rise to localize d superconducting edge states near any free boundary, thickness jump o r local variation of the vector potential. We have investigated a thin superconducting film with an array of patterned microholes. A splitti ng of the critical held line is found when the field is perpendicular to the film. The new transition line (H-c3) exhibits two types of fine structure due to the quantization of the multiply connected edge stat es. Fire discuss these states in terms of multiquanta vortices nucleat ed inside the holes. We report Bitter decoration of the the correspond ing vortex configuration. Because of the enhancement of the order para meter near the hole edges, the interaction between the vortices and th e microholes is repulsive slightly below the bulk critical held (H-c2) and is much stronger than the intervortex interaction. We find a ''lo calization transition'': all vortices drop inside holes when the coher ence length becomes larger than the interhole spacing. This transition explains the two types of oscillation found in the transition line an d leads to a qualitative change of the creep below the second critical field.