6533b852fe1ef96bd12aabaa

RESEARCH PRODUCT

Flux-flow instability and its anisotropy inBi2Sr2CaCu2O8+δsuperconducting films

subject

description

We report measurements on voltage instability at high flux-flow velocities in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ superconducting films. Current-voltage $(I\ensuremath{-}V)$ 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 $I\ensuremath{-}V$ 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 ${I}^{*}{(T,H)=I}^{*}(H)(1\ensuremath{-}{T/T}_{\mathrm{co}}{)}^{3/2}$ with ${I}^{*}(H)\ensuremath{\propto}{1/(1+H/H}_{0}{)}^{\ensuremath{\alpha}}$, where ${T}_{\mathrm{co}},$ ${H}_{0},$ and \ensuremath{\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.