Vortex instability and the normal state at low temperatures

The motion of flux vortices in Y1Ba2Cu3O7-delta has been studied in the low temperature limit (T similar to 2% of T-c) at extreme current and dissipat ion densities (P/V similar to 10(9) W/cm(3)). Beyond the regime where flux motion is driven into free how, occurs an instability that seems to arise f rom a suppression of the order parameter. The critical resistivity at the p oint of instability is roughly twice the free-flux-flow value rho*/rho (n) similar to 2 rho (f) similar to 2B/H-c2, allowing an estimation of the illu sive normal-state resistivity, p(n), in the zero-temperature limit. The est imated p(n) saturates to a finite residual value, like a conventional eleme ntal superconductor, and the vortex dissipation continues to be finite as T --> 0.