Pinning effects on flux flow instability in epitaxial Nb thin films

Abstract

The flux flow properties of epitaxial niobium films with different pinning strengths are investigated by dc electrical resistance measurements and mapped to results derived within the framework of a theoretical model. Investigated are the cases of weak random pinning in as-grown films, strong random pinning in Ga ion-irradiated films, and strong periodic pinning induced by a nanogroove array milled by focused ion beam. The generic feature of the current-voltage curves of the films consists in instability jumps to the normal state at some instability current density $j^{\ast }$ as the vortex lattice reaches its critical velocity $v^{\ast }$. While $v^{\ast }(B)$ monotonically decreases for as-grown films, the irradiated films exhibit a non-monotonic dependence $v^{\ast }(B)$ attaining a maximum in the low-field range. In the case of nanopatterned films, this broad maximum is accompanied by a much sharper maximum in both, $v^{\ast }(B)$ and $j^{\ast }(B)$, which we attribute to the commensurability effect when the spacing between the vortex rows coincides with the location of the grooves. We argue that the observed behavior of $v^{\ast }(B)$ can be explained by the pinning effect on the vortex flow instability and support our claims by fitting the experimental data to theoretical expressions derived within a model accounting for the field dependence of the depinning current density.

7 pages, 6 figures, accepted for publication in Supercond. Sci. Technol

References in corpus (4)

• Rearrangement of the vortex lattice due to instabilities of vortex flow
• AC-driven Vortices and the Hall Effect in a Superconductor with a Tilted Washboard Pinning Potential
• Evidence of a new low field cross-over in the vortex critical velocity of type-II superconducting thin films
• Pinning effects on hot-electron vortex flow instability in superconducting films

Cited by in corpus (5)

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• Supersonic dynamics of guided magnetic flux quanta
• Rising speed limits for fluxons via edge quality improvement in wide MoSi thin films
• Vortex counting and velocimetry for slitted superconducting thin strips
• Fast Dynamics of Vortices in Superconductors