Dynamic Matching of Vortex Lattice in Superconducting Multilayers

We observed oscillations of a nonlinear flux flow resistivity $R(j,H)$ as a function of a parallel magnetic field $6<H<\mathrm{}9\mathrm{}\mathrm{T}$ in Nb-Ti/Cu multilayers. We show that the oscillations in $R\left(H\right)$, which have the field period $\Delta H\approx 0.1\mathrm{T}$ independent of temperature and current, indicate a long-range order in the rapidly moving vortex structure. The critical current $I_c\left(H\right)$ exhibits no oscillations characteristic of $R\left(H\right)$. We propose an explanation of the effect in terms of dynamic matching of the moving vortex lattice with periodic microstructure and show that both $\Delta H$ and the amplitude of the oscillations of $R\left(H\right)$ are inversely proportional to the sample thickness.