Thermal effects in YBCO/metal bilayers at high current densities

Abstract

We report on the thermal aspects associated with the switching properties at high current densities of YBCO thin films shunted by a metallic layer. The role of the shunt is first detailed in a current ramp mode experiment under various conditions of temperature and magnetic field. We discuss specifically a regime associated with an almost total current diversion by the metallic layer, observed when the critical current density is reduced at temperatures close to the critical temperature T c or under magnetic field. This regime is associated to a thermal anomaly, as seen in the temperature signal measured on the rear side of the substrate, which can explain the partial recovery of the superconductive state under magnetic field. Under current limitation conditions at 50 Hz, 77 K and self-field, the temperature reaches 260 K at the rear side of the sapphire substrate after 0.4 s without any damage to the superconducting device.