A MEAN-FIELD DESCRIPTION OF THE TRANSITION TO THE MIXED-STATE OF SUPERCONDUCTING MICROBRIDGES WITH LOW VORTEX PINNING FORCES

We propose a mean field description of the phenomena occurring in supe rconducting thin film microbridges with low pinning forces when vortic es are nucleated. This model allows for computation of the vortex velo city, the penetration depth, the critical current density and the vort ex nucleation field in a microbridge from its dimensions, its current voltage characteristics, and the coherence length of the microbridge m aterial. Moreover the effect of an external magnetic field is shown to be strongly dependent on its spatial distribution. The model predicti ons are compared to experimental results obtained from TlBaCuO and YBa CuO vortex flux transistors and a long YBaCuO microbridge.