Non-Ohmic dissipative regime in the superconducting transition of polycrystalline Y1Ba2Cu3Ox

Abstract

We have measured the low-field magnetoresistance and current-voltage characteristics of polycrystalline ${\mathrm{Y}}_1$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ near the superconducting-normal transition. The development of a fully superconducting state occurs via an intermediate phase about 2 K in width. Within this intermediate phase, sample dissipation is highly non-Ohmic and exhibits extreme sensitivity to small magnetic fields. The nonlinear I-V characteristics describe a new phase with zero resistance and zero critical current which seems to arise from the presence of strong junction disorder.