Transition to the normal state of superconducting Y1Ba2Cu3O7-δ thin films induced by high current densities

We report measurements at zero applied magnetic field of the characteristic curves (E-J) in Y1Ba2Cu3O7-delta thin films in the high current density regime, up to current densities which induce the transition to the normal state. To minimize spurious heating effects due to Joule dissipation, the E-J curves were measured with a pulse technique and with the samples submerged in a liquid nitrogen bath, changing the temperature by varying the nitrogen vapour pressure. This experimental set-up allows us to observe not only the abrupt voltage jump appearing at current densities J* much larger (typically one order of magnitude) than the critical current density, J(c), but also the entire transition up to the normal state. Our results show that the product J*rho (n) is roughly sample independent, rho (n) being the slope of the E-J curves for J>J*. This finding is in qualitative agreement with the existing models that explain the jump at J* in terms of a vortex instability at high flux-flow velocities.