Excess flux stability fingerprints in the I_c(B)-T_c(B) phase boundary of superconducting thin films with quasiperiodic microtopology

TL;DR

This study experimentally explores how quasiperiodic microtopology in superconducting niobium thin films influences the magnetic field dependence of critical current and transition temperature, revealing unique excess flux stability fingerprints.

Contribution

It provides the first experimental observation of modulations in the phase boundary caused by quasiperiodic microtopology, confirming predictions from numerical simulations.

Findings

Modulations in the phase boundary for quasiperiodic tilings

Excess flux densities slightly higher than matching flux show unique effects

Quasiperiodic caging and giant vortices explain the observed effects

Abstract

We experimentally investigate the magnetic field $B$ dependence of the critical current I_c and the transition temperature T_c, i.e. the I_c(B)-T_c(B) phase boundary, of superconducting niobium thin films patterned with periodic and quasiperiodic antidot arrays on the submicron scale. For this purpose we monitor current-voltage characteristics at different values of B and T. We investigate samples with antidots positioned at the vertices of two different tilings with quasiperiodic symmetry, namely the Shield Tiling and the Tuebingen Triangle Tiling. For reference we investigate a sample with a triangular antidot lattice. We find modulations of the phase boundary for both quasiperiodic tilings, which were predicted by numerical simulations but not observed in experiments yet. The particularity of these commensurability effects is that they correspond to excess flux densities, which are slightly higher than the matching flux. The observed matching effects can be explained by quasiperiodic caging of interstitial vortices and/or the formation of symmetry induced giant vortices.