Giant vortex state in perforated aluminum microsquares

TL;DR

This paper explores how perforations in aluminum microsquares influence superconductivity, revealing fluxoid quantization effects at low fields and a giant vortex state at high fields, supported by Ginzburg-Landau theory analysis.

Contribution

It demonstrates the transition from fluxoid quantization oscillations to a giant vortex state in perforated superconducting squares, highlighting the impact of geometry on superconducting behavior.

Findings

Fluxoid quantization causes T_c(H) oscillations at low fields.

Giant vortex state emerges at high magnetic fields.

Geometry significantly influences the superconducting phase boundary.

Abstract

We investigate the nucleation of superconductivity in a uniform perpendicular magnetic field H in aluminum microsquares containing a few (2 and 4) submicron holes (antidots). The normal/superconducting phase boundary T_c(H) of these structures shows a quite different behavior in low and high fields. In the low magnetic field regime fluxoid quantization around each antidot leads to oscillations in T_c(H), expected from the specific sample geometry, and reminiscent of the network behavior. In high magnetic fields, the T_c(H) boundaries of the perforated and a reference non-perforated microsquare reveal cusps at the same values of Phi/Phi_0 (where Phi is the applied flux threading the total square area and Phi_0 is the superconducting flux quantum), while the background on T_c(H) becomes quasi-linear, indicating that a giant vortex state is established. The influence of the actual geometries on T_c(H) is analyzed in the framework of the linearized Ginzburg-Landau theory.