Decoupling transition of two coherent vortex arrays within the surface superconductivity state

TL;DR

This study investigates the decoupling transition of surface vortices in niobium films under tilted magnetic fields, revealing a transition from coherent to independent vortex behavior and its impact on pinning properties.

Contribution

It demonstrates the decoupling transition of surface vortices in niobium films and links it to changes in pinning, providing new insights into vortex dynamics in layered superconductors.

Findings

Decoupling transition occurs in surface vortex arrays under tilted magnetic fields.

Pinning properties change significantly at the transition point.

Surface vortices behave coherently or independently depending on the magnetic field orientation.

Abstract

In magnetic fields applied within the angular range of the surface superconductivity state a magnetically anisotropic layered medium is created in structurally isotropic, sufficiently thick niobium films. Surface (Kulik) vortices residing in the superconducting sheaths on both main film surfaces in tilted fields are shown to undergo a decoupling transition from a coherent to an independent behavior, similar to the behavior observed for Giaever transformer. At the transition a feature in pinning properties is measured, which implies different pinning for the lattice of surface vortices coherently coupled through the normal layer and for two decoupled vortex arrays in the superconducting surface sheaths.