Measurements of the fluctuation magnetization around TC in a YBa2Cu3O7 crystal: Determination of the critical-region width

We present measurements of the fluctuation-induced magnetization around the superconducting transition in a YBa2Cu3O7 single crystal. The data were analyzed in terms of the Ginzburg–Landau theory for multilayered superconductors. The simultaneous analysis in the low magnetic field region above TC0 and in the high magnetic field region around TC(H) allowed us to obtain accurate information on the critical region width (which was found to be in excellent agreement with the prediction of the Ginzburg criterion) and also on the ratio of Josephson couplings between the different superconducting layers.