Current-induced phase transition of moving vortices in untwinned YBa2Cu3O7−δ single crystals

To study the phase transition of vortices induced by current flow, the electrical resistivity and the voltage–current characteristic have been measured on untwinned ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ single crystals in a magnetic field parallel to the $c$ axis. Near a first-order melting transition (FOMT) line, the well-known counterclockwise hysteresis of resistivity drop disappears completely above a certain current density while a novel clockwise hysteresis appears just below this resistivity drop. Moreover, the voltage–current characteristic does not show any Ohmic behavior as the current increases near the FOMT line. The obtained results are explained by the current-induced melting of the vortex lattice or smectic similar to an increase in the temperature or the magnetic field.