Fast Dynamics of Guided Magnetic Flux Quanta

Abstract

The dynamics of Abrikosov vortices in superconductors is usually limited to vortex velocities $v\simeq1$ km/s above which samples abruptly transit into the normal state. In the Larkin-Ovchinnikov framework, near the critical temperature this is because of a flux-flow instability triggered by the reduction of the viscous drag coefficient due to the quasiparticles leaving the vortex cores. While the existing instability theories rely upon a uniform spatial distribution of vortex velocities, the measured (mean) value of $v$ is always smaller than the maximal possible one, since the distribution of $v$ never reaches the $\delta$-functional shape. Here, by guiding magnetic flux quanta at a tilt angle of $15^\circ$ with respect to a Co nanostripe array, we speed up vortices to supersonic velocities. These exceed $v$ in the reference as-grown Nb films by almost an order of magnitude and are only a factor of two smaller than the maximal vortex velocities observed in superconductors so far. We argue that such high $v$ values appear in consequence of a collective dynamic ordering when all vortices move in the channels with the same pinning strength and exhibit a very narrow distribution of $v$. Our findings render the well-known vortex guiding effect to open prospects for investigations of ultrafast vortex dynamics.