Critical field behavior of a multiply connected superconductor in a tilted magnetic field

TL;DR

This study investigates the critical magnetic field behavior of thin aluminum superconducting films on a perforated substrate, revealing complex reentrant phenomena and the influence of field orientation on superconductivity.

Contribution

It provides new insights into how tilted magnetic fields affect the critical behavior of multiply connected superconductors with nanoscale hole arrays.

Findings

Reentrant superconductivity at a specific matching field.

Critical field position scales with sec(θ) in tilted fields.

Enhanced dissipation occurs when the perpendicular component matches the matching field.

Abstract

We report magnetotransport measurements of the critical field behavior of thin Al films deposited onto multiply connected substrates. The substrates were fabricated via a standard electrochemical process that produced a triangular array of 66 nm diameter holes having a lattice constant of 100 nm. The critical field transition of the Al films was measured near $T_c$ as a function of field orientation relative to the substrate normal. With the field oriented along the normal ($\theta=0$), we observe reentrant superconductivity at a characteristic matching field $H_m=0.22\,\mathrm{T}$, corresponding to one flux quantum per hole. In tilted fields, the position $H^*$ of the reentrance feature increases as $\sec(\theta)$, but the resistivity traces are somewhat more complex than those of a continuous superconducting film. We show that when the tilt angle is tuned such that $H^*$ is of the order of the upper critical field $H_c$, the entire critical region is dominated by the enhanced dissipation associated with a sub-matching perpendicular component of the applied field. At higher tilt angles a local maximum in the critical field is observed when the perpendicular component of the field is equal to the matching field.