Penetration Depth Measurements and Associated Phenomenology in High-Tc Superconductors

Measurements of the penetration length lambda of c-axis oriented thin films of YBa sub 2 Cu sub 3 O sub 7 in magnetic fields H as high as 14 T enable a determination of the transition temperature T sub c(H) by extrapolation to lambda=infinity. For fields in the range 1 T ~ H = 14 T, lambda(H,T) is found to have a square-root dependence on H and a temperature dependence near T sub c which reduces to that expected for an array of Josephson-coupled proximity junctions.