Anomalous temperature dependence of vortex elastic properties in the flux-flow regime ofMo77Ge23/Ge multilayer superconductors

We report nonlinear electrical response in superconducting/insulating ${\mathrm{Mo}}_{77}$ ${\mathrm{Ge}}_{23}$/Ge multilayers. In low-anisotropy multilayers, we observe an abrupt change in the current-voltage characteristic as a function of temperature. This change corresponds to a sharp drop in the pinning drag force acting on moving vortices in the flux-flow regime at low temperatures. The decrease in pinning drag force may be related to an abrupt increase in the rigidity of the system of moving vortices.