Onset, evolution, and magnetic braking of vortex lattice instabilities in nanostructured superconducting films

Abstract

In 1976 Larkin and Ovchinnikov [Sov. Phys. JETP 41, 960 (1976)] predicted that vortex matter in superconductors driven by an electrical current can undergo an abrupt dynamic transition from a flux-flow regime to a more dissipative state at sufficiently high vortex velocities. Typically this transition manifests itself as a large voltage jump at a particular current density, so-called instability current density J * , which is smaller than the depairing current. By tuning the effective pinning strength in Al films, using an artificial periodic pinning array of triangular holes, we show that a unique and well defined instability current density exists if the pinning is strong, whereas a series of multiple voltage transitions appear in the relatively weaker pinning regime. This behavior is consistent with time-dependent Ginzburg-Landau simulations, where the multiple-step transition can be unambiguously attributed to the progressive development of vortex chains and subsequently phase-slip lines. In addition, we explore experimentally the magnetic braking effects, caused by a thick Cu layer deposited on top of the superconductor, on the instabilities and the vortex ratchet effect.

Parabolic temporal profiles of non-spanning avalanches and their importance for ferroic switching

“…Averaged jerk profiles have been determined so far for slip avalanches in metallic glasses, 25 deformations during crystal plasticity, 26 in granular materials, 27 shear bands, 28 and superconductors. 29 Simulations of jerk profiles in ferroelastic materials seem to confirm the parabola hypothesis 30 although this work combined spanning avalanches ("large avalanches") at yield points with more local switching avalanches ("small avalanches"). A similar distinction was made between "small slip avalanches" and "large slip avalanches" in metallic glasses 25 and related to different physical processes underlying the small and large slip process.…”

Velocimetry of superconducting vortices based on stroboscopic resonances

“…Furthermore, by substituting the characteristic values of ξ (0) and T c for different materials one can easily compare the vortex velocities to be expected. Using the parameters of Al ( ξ (0) = 90 nm, τ GL (0) = 0.38 ps, T c = 1.37 K 42 ) and Pb ( ξ (0) = 33 nm, τ GL (0) = 72 fs, T c = 7.2 K 43 ), one obtains the velocity multiplier ratios: and , estimating expected velocity for Abrikosov vortices to be significantly larger than in NbN.…”

Open circuit voltage generated by dragging superconducting vortices with a dynamic pinning potential

“…In what follows, we adopt ξ=73.8 nm, κ=4 and w=2.4 μm in our simulations [39,40]. For comparison, typical Nb thin films have ξ(0)=10 nm and κ=15 [41], for Al films it has been previously reported ξ(0)=90 nm and κ∼2 [42], whereas for Pb, ξ(0)=34 nm and κ∼2 [43]. Since the effective penetration depth is dependent on the thickness of the superconducting film, it can be varied in a large range of values without significantly altering T c or ξ.…”