Central peak position in magnetization loops of high-T-c superconductors

Exact analytical results are obtained for the magnetization of a supercondu cting thin strip with a general behavior J(c)(B) of the critical current de nsity. We show that within the critical-state model the magnetization as a function of applied field, B-a, has an extremum located exactly at B-a = 0. This result is in excellent agreement with presented experimental data for a YBa2Cu3O7-delta thin film. After introducing granularity by patterning t he him, the central peak becomes shifted to positive fields, B-cp > 0, on t he descending field branch of the loop. Our results show that a positive B- cp is a definite signature of granularity in superconductors. [S0031-9007(9 9)08821-3].