Vortex dynamics in YBa2Cu3O7−δ superconducting films: Experimental evidence for an instability in the vortex system at high current densities

Abstract

Current-voltage characteristics and the temperature dependence of the electrical resistivity of YBa2Cu3O7−δ thin films were investigated in magnetic fields up to 5 T. For a given magnetic field, both voltage and resistivity jumps could be observed at high driving forces when the current density and the temperature reached the critical values J* and T*, respectively. Excellent scaling of the experimental data was obtained by describing the field and temperature dependence by J*(H,T)=J*(T)/(1+H/H0)α and J*(T)∼(1-T/Tc0)3/2 with 1/3≤α≤3/4 and H0 and Tc0 being constants. These results indicate a well-defined vortex instability closely resembling that predicted by Larkin and Ovchinnikov (LO) for high flux flow velocities. In the present case, however, by referring to the current-voltage (I-V) characteristics, this instability can be demonstrated to occur even at temperatures well below Tg defined by separating negatively from positively curved I-V characteristics. Analyzing the experimentally observed instability according to LO theory, the temperature dependence of the inelastic quasiparticle scattering time has been obtained. As a new aspect, the corresponding critical flux-flow velocity exhibits a significant field dependence for small magnetic fields, while for fields above 2 T this dependence seems to disappear. © 1996 The American Physical Society.

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