THE MEISSNER AND SHIELDING EFFECTS OF HIGH-TEMPERATURE OXIDE SUPERCONDUCTORS

The Meissner and shielding effects were investigated systematically on single crystals of (La1-xSrx)2CuO4, YBa2Cu3O7 and Bi2Sr1.8CaCu2O8. Si gnificant differences in the low-temperature Meissner fraction (f(M)) in the same materials observed under various fields and sample sizes, were explained consistently and quantitatively, based on the vortex-pi nning model. Extending the model employed, the pinning critical curren t could be estimated as a function of T from the set of the shielding and Meissner curves. The Meissner and shielding effects in the polycry stalline samples were also measured in a similarly systematic manner a nd could be interpreted by considering the effective sample size of th e polycrystals, showing a cross-over of this quantity from the grain s ize at high fields to macroscopic sample size at low fields.