Josephson-like effects in coherent motion of vortices in a periodic potential

Resonant quasi-Josephson effects induced by coherent vortex motion in artif icial reversible periodic potential structures have been investigated. Peri odic potential has been imposed by application of a magnetic tape containin g a prerecorded harmonic signal to the surface of a high-T-c, thin film str ip. Motion of current driven vortices in the film with applied tape is high ly coherent and leads to the appearance of a series of self-resonant DC cur rent steps on the I-V characteristic of the sample. The presented model att ributes these steps to locking of the vortex nucleation frequency to the in ternal self-frequencies of the system; the latter being set by the time of flight of vortex bundles across the sample width and across the spatial per iod of the applied potential. Voltages of the current steps have been found to scale consistently with the proposed model. The velocity of vortex moti on inferred from the voltages of the first quasi-Josephson steps was found to be extremely large. The possible explanation of this fact in terms of th e huge size of vortex bundles is discussed and confronted with independent experimental evaluations of the bundle size from the flux-flow noise spectr a and vortex induced random telegraph voltages in high-T-c, superconductors . (C) 2000 Elsevier Science B.V. All rights reserved.