Crossover between the classical friction and the nano-scale friction investigated by the transient dynamics of vortices in La2-xSrxCuO4 thin films

Abstract

We investigated the dynamics of driven vortices in high-Tc superconductor from the viewpoint of the physics of friction. First of all, for all samples, we found the obvious waiting-time dependence of the maximum static friction force which is proportional to the critical current density, below the glass-liquid transition line. This indicates that the dynamics of vortices is like the nano-scale(microscopic) friction, where the relaxation occurs frequently. As temperature decreased, the waiting-time dependence dissapeared, impling that the vortex dynamics became that of classical(macroscopic) friction, where the relaxation rarely occurs. The crossover line of the relaxation phenomena depended on the bridge size. From the results obtained in this paper, we propose a universal parameter which discriminates the macroscopic friction from the microscopic friction.