Static and dynamic shear response in ultrathin layers of vortex matter

We report on experiments in which ultrathin layers of vortex matter are she ared along nanofabricated Row channels in a NbN/Nb3Ge double layer. The str ucture of the vortex matter inside the channels can he tuned continuously, via the applied magnetic field, from ordered, dose-packed crystalline to hi ghly disordered, amorphous configurations. We explore the evolution of the static and dynamic response as vortex matter inside the channels is built u p row by row and analyze our results in terms of an effective static and dy namic friction. From the current and field dependence of this vortex fricti on, together with characteristic signatures in the measured velocity fluctu ations, we find that ultrathin layers containing up to six commensurate vor tex rows behave similar to brittle solids, while wider layers exhibit chara cteristics more akin to plastic flow.