High-current differential resistance in Bi2Sr2CaCu2O8 single crystals

We have studied the post threshold voltage response in the a-b plane of Bi2 Sr2CaCu2O8 single crystals to short (< 100 mus) current pulses, Current den sities in the a-b plane in excess to 4 x 10(8) Am-2 have been investigated as a function of temperature down to 5 K and c-axis directed magnetic field up to 7 T. We find a current-independent differential resistance R-f in th e high-current limit well beyond threshold. In the vortex solid phase, R-f is independent of temperature and of the magnetic field in a broad range of fields (0.5 to 7 T). The Lorentz-force-independent differential resistance in the solid phase suggests either a viscosity proportional to magnetic fi eld in the flux-flow picture or a non-flux-flow (possibly phase fluctuation ) origin of a-b plane dissipation.