The paraconductivity of granular Al-films at high reduced temperatures and magnetic fields

TL;DR

This study investigates the paraconductivity in granular aluminum films at high reduced temperatures and magnetic fields, revealing strong Josephson coupling and high Tc values due to fluctuation effects and a total-energy cutoff.

Contribution

It introduces a model incorporating a total-energy cutoff to explain anomalous fluctuation behavior and accurately determines coherence lengths in granular Al films.

Findings

Coherence lengths are 20-48 nm, larger than grain sizes.

Grains are strongly Josephson-coupled.

Tc is up to twice the bulk value.

Abstract

The electrical conductivity induced near the superconducting transition by thermal fluctuations was measured in different granular aluminum films. The seemingly anomalous behavior at high reduced temperatures and magnetic fields is explained by taking into account a total-energy cutoff in the superconducting fluctuation spectrum in both the direct (Aslamazov-Larkin) and the indirect (anomalous Maki-Thompson) contributions to the fluctuation effects. The analysis allowed a reliable determination of the coherence length amplitudes, which resulted to be much larger (20-48 nm) than the grains size (5-10 nm). This suggests that the grains are strongly Josephson-coupled, while the Tc value is still as high as twice the bulk value. These results could contribute to identify the mechanisms enhancing Tc in these materials.