Dynamic vortex instabilities in Ta/Ge-based multilayers and thin films with various pinning strengths

摘要

We report measurements of a dynamic instability in the moving vortex system of Ta/Ge-based thin films and multilayers. The instability results from a nonequilibrium distribution of quasiparticles induced by motion of the vortex cores, as described theoretically by Larkin and Ovchinnikov in the regime where there is no pinning. For the Ta/Ge system, where the critical vortex velocity is relatively small, we observe the instability in cases where either the viscosity or pinning dominate the vortex motion. We develop a simple model to describe the effects of pinning on the flux motion near the instability, and show that it gives a good description of the experimental data, especially in fields not too close to ten. The temperature dependence of the critical vortex velocity extracted from the analysis indicates that electron-electron scattering provides the dominant contribution to the energy relaxation. [References: 22]