Study of the vortex state in YBa 2Cu 3O 7 and Bi 2Sr 2CaCu 2O x by the NMR decoration technique

Abstract

The field inhomogeneity in the mixed state of a type II superconductor can be studied by the NMR decoration technique. We calibrated this technique using the classical superconductor Nb 3Sn [1]. As NMR probe we have taken thin silicone oil layers formed around the individual grains of superconducting powder. We measured the additional NMR line broadening of the oil as a function of temperature. This method is applied to study the characteristic field inhomogeneity of YBa 2Cu 3O 7 (YBCO) and Bi 2Sr 2CaCu 2O x (BSCCO) powders in the field cooled and zero field cooled regimes. For YBCO, the temperature dependence of the additional line broadening follows the temperature dependence of the penetration depth given by the fwo fluid model. The penetration depth λ 0=3040 Å for YBCO derived from the two fluid model fit, is an average over different grain orientations and lies in between the values λ ab and λ c reported previously [2]. For BSCCO, the additional line broadening vs temperature strongly deviates from the predicton based on the two fluid model.