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

TL;DR

This study investigates vortex lattice instabilities in nanostructured superconducting films, revealing how pinning strength influences the nature of the transition and exploring magnetic braking effects on vortex dynamics.

Contribution

It demonstrates the existence of a unique instability current density under strong pinning and identifies multiple voltage transitions under weaker pinning, supported by Ginzburg-Landau simulations.

Findings

Strong pinning yields a single well-defined instability current density.

Weak pinning results in multiple voltage transitions.

Magnetic braking affects vortex instabilities and ratchet effects.

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