Reentrant AC magnetic susceptibility in Josephson-junction arrays: An alternative explanation for the paramagnetic Meissner effect

TL;DR

This paper demonstrates that reentrant paramagnetic behavior in Josephson-junction arrays can be explained by a simple loop model, providing an alternative to the π-junction explanation for the paramagnetic Meissner effect.

Contribution

It introduces a simplified loop model that accounts for the paramagnetic response in Josephson arrays without invoking π-junctions, challenging previous interpretations of PME.

Findings

Reentrant paramagnetic response observed in Josephson arrays.

A single-loop model explains the paramagnetic contribution.

The model's parameter range matches experimental observations.

Abstract

The paramagnetic Meissner effect (PME) measured in high $T_{C}$ granular superconductors has been attributed to the presence of $\pi$-junctions between the grains. Here we present measurements of complex AC magnetic susceptibility from two-dimensional arrays of conventional (non $\pi$) Nb/Al/AlOx/Nb Josephson junctions. We measured the susceptibility as a function of the temperature $T$, the AC amplitude of the excitation field, $h_{AC}$, and the external magnetic field, $H_{DC}$. The experiments show a strong paramagnetic contribution from the multi-junction loops, which manifests itself as a reentrant screening at low temperature, for values of $h_{AC}$ higher than 50 mOe. A highly simplified model, based on a single loop containing four junction, accounts for this paramagnetic contribution and the range of parameters in which it appears. This model offers an alternative explanation of PME which does not involve $\pi$-junctions.