Electric field effects on vortex dynamics in ultrathin ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ films

The effects of charge-carrier density modulation on critical currents and vortex dynamics in ultrathin ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ films were investigated through transport measurements in field-effect devices. Two distinct dissipation regions in resistive transitions in applied magnetic fields are identified by the electric-field effect. A Kosterlitz-Thouless-like transition is observed in zero magnetic field, which can be tuned by the electric field. The importance of thermal fluctuations for the dissipation in high-${\mathit{T}}_{\mathit{c}}$ superconductors is stressed.