In order to understand the nature of the mixed state, the critical current density Jc of Nb/NbZr multilayers was measured as a function of magnetic field H and of the angle between H and the film plane at the temperatures where the superconducting order parameter is localized in the Nb layers. In the parallel fields, which are perpendicular to the current J, the Jc-H curves show a peak at H=Hmax. The observed angular dependence of Jc below and above Hmax can be explained by the 3D stepwise vortex model and the 2D pancake vortex model, respectively. These results indicate that a dimensional crossover in the mixed state occurs at Hmax. This crossover may be the cause of the field dependence of Jc which is an increasing function of H below Hmax.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering