Current-driven vortex state inBi2Sr2CaCu2O8+δwith columnar defects

The effects of applied current on the vortex-lines dynamics in heavy-ion-irradiated ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ are studied through Monte Carlo simulation. From the analysis of current-voltage characteristics, we find a clear peak effect in the critical current density, prominent near the melting transition of the vortex solid, when the magnetic field is increased toward the matching field. The peak field corresponds to a fractional $(\ensuremath{\approx}1/3)$ filling factor of the vortices to columnar defects. This enhanced vortex pinning occurs simultaneously with a rapid change in the interlayer-coupling nature of the current-driven vortex state. In addition, numerical results on current-driven moving vortex lines could also explain other anomalies obtained from the recent Josephson plasma measurements.