Vortex structure and resistive transitions in high-T-c superconductors

The nature of the resistive transition for a current applied parallel to the magnetic field in high-T-c materials is investigated by numerical simulation on the three-dimensional Josephson junction array model. Using finite-size scaling it is shown that for samples with disorder the temperature T-p of the c-axis resistivity transition corresponds to a percolation phase transition of vortex lines perpendicularly to the applied field. The value of T-p is higher than the temperature of the resistive transition for j perpendicular to H, but decreases with the thickness of the sample and with anisotropy. We predict that critical behavior around T-p should reflect in experimentally accessible quantities, as the I-V curves.