Onset of the 0-dimensional vortex pinning behavior in the optimally doped and overdoped Bi2Sr2CaCu2O8+delta system

We report results of transverse AC magnetic permeability in the linear regi me and DC magnetization loops for optimally doped and oxygen overdoped samp les of Bi2Sr2CaCu2O8+delta The data cover the low temperature (T < 25K) and low held (H-a < 1000 Oe) region of the magnetic (H-a-T) phase diagram. In optimally doped as well as in overdoped samples a crossover to a O-dimen sional pinning regime (Larkin length, L-C(C), shorter than the inter-plane CuO2 distance) is observed at a characteristic temperature Too for all inve stigated fields. The order-disorder transition, identified by the second peak in magnetizati on and a non monotonous field dependence of the AC penetration depth, is qu enched below T-0D.