Current-induced highly dissipative domains in high-T c thin films

We have investigated the resistive response of high-${T}_{c}$ thin films submitted to a high density of current. For this purpose, current pulses were applied into bridges made of ${\mathrm{Nd}}_{1.15}{\mathrm{Ba}}_{1.85}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ and ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}.$ By recording the time-dependent voltage, we observe that at a certain critical current ${j}^{*},$ a highly dissipative domain develops somewhere along the bridge. The successive formation of these domains produces stepped $I\ensuremath{-}V$ characteristics. We present evidence that these domains are not regions with a temperature above ${T}_{c},$ as for hot spots. In fact this phenomenon appears to be analog to the nucleation of phase-slip centers observed in conventional superconductors near ${T}_{c},$ but here in contrast they appear in a wide temperature range. Under some conditions, these domains will propagate and destroy the superconductivity within the whole sample. We have measured the temperature dependence of ${j}^{*}$ and found a similar behavior in the two investigated compounds. This temperature dependence is just the one expected for the depairing current, but the amplitude is about 100 times smaller.