Flux-flow instability and its anisotropy in Bi2Sr2CaCu2O8+δ superconducting films

We report measurements on voltage instability at high flux-flow velocities in Bi2Sr2CaCu2O8 + delta superconducting films. Current-voltage (I - V) characteristics have been measured as a function of temperature, magnetic field, and angle between the field and the c axis of the sample. Voltage jumps were observed in I-V characteristics taken in all magnetic-field directions and in extended temperature and field ranges. An analysis of the experimental data, based on a theory for viscous flux-flow instability with a finite heat-removal rate from the sample, yielded the inelastic scattering rate and the diffusion length of quasiparticles. Reasonable values of the heat-transfer coefficient from film to bath have been obtained. This theory can also successfully explain the observed scaling behavior I*(T,H) = I*(H)(1 - T/T-co)(3/2) with I*(H) proportional to 1/(1 + H/H-0)(alpha), where T-co, H-0, and alpha are fitting parameters, determined by the temperature and magnetic-field dependence of the critical current I* at which the voltage jumps occur. A two-dimensional scaling for the angular dependence of the critical current I* and the critical voltage V* associated with the voltage jump has been found and interpreted with a model based on the two-dimensional behavior of this system. [S0163-1829(99)10901-9].