Current-driven vortex dynamics in a periodic potential

Quasi-Josephson effects due to coherent vortex motion in artificial reversi ble periodic potential structures in high-T-c superconducting thin films ha ve been investigated. Periodic pinning conditions have been created by appl ying a magnetic tape containing a prerecorded harmonic signal to the surfac e of high quality Y1Ba2Cu3O7-delta thin films. Application of the periodic pinning enforces coherence in current-driven motion of Abrikosov vortices i n wide and short macrobridges and leads to the appearance of Josephson-like effects manifesting themselves in series of self-induced current steps on the current-voltage characteristics. The equation of motion for vortices fl owing across periodic potential structures is analogous to the phase equati on for low-capacitance classical Josephson junctions. The perturbation solu tions of this equation contain resonant Shapiro-like self-steps resulting f rom the locking of the frequency at which vortices are created at the sampl e borders to the resonant frequencies of the vortex system. Self-resonant f requencies are set by the characteristic time of flight across the sample w idth and across the period of the applied potential. Voltages of the self-i nduced current steps have been found to scale with inverse of the character istic length corresponding to the magnetic period and/or to the sample half -width, consistently with the theoretically derived relations. Experimental data indicate that vortices move in large bundles containing several thous ands of flux quanta. The temperature dependence of the step voltages can be ascribed to changes in vortex velocity due to the temperature-dependent vi scosity factor. [S0163-1829(99)01334-X].