STSM of Volodymyr Bevz at the Goethe University Frankfurt (Germany)
The purpose of the STSM was to explore the vortex dynamics in superconductor-based hybrid structures fabricated by focused ion and electron beam induced deposition. The motivation and major results of this research were the following: The dynamics of Abrikosov vortices in superconductors is usually limited to vortex velocities v ≈ 1 km/s, above which samples abruptly transit into the normal state. In the Larkin-Ovchinnikov framework, near the critical temperature, this transition 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 δ -functional shape. In the course of the STSM, by guiding magnetic ﬂux quanta at a small tilt angle of with respect to a Co nanostripe array, we speeded up vortices to 3–6 km/s. These velocities exceed the vortex velocities in the reference as-grown Nb ﬁlms by almost an order of magnitude and 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 have rendered the well-known vortex guiding eﬀect as toolbox for investigations of ultrafast vortex dynamics and are published in Phys. Rev. Appl. 11, 054064 (2019).