Shell Structure and Strengthening of Superconducting Pair Correlation in Nanoclusters

TL;DR

This paper explores how shell structure in metallic nanoclusters can lead to strong superconducting pairing, potentially resulting in high critical temperatures and observable spectroscopic effects.

Contribution

It demonstrates that shell degeneracy and specific cluster configurations can significantly enhance superconducting pairing in nanoclusters, with implications for high Tc superconductivity.

Findings

High Tc values predicted for certain nanoclusters

Strong alteration of energy spectrum due to pairing

Odd-even spectral effects indicative of pairing

Abstract

The existence of shell structure and the accompanying high degeneracy of electronic levels leads to the possibility of strong superconducting pairing in metallic nanoclusters with N~100-1000 delocalized electrons. The most favorable cases correspond to (a) "magic" clusters with strongly degenerate highest occupied and lowest unoccupied shells and a relatively small energy spacing between them as well as to (b) clusters with slightly incomplete shells and small Jahn-Teller splitting. It is shown that realistic sets of parameters lead to very high values of Tc as well as to a strong alteration of the energy spectrum. The impact of fluctuations is analyzed. Spectroscopic experiments aimed at detecting the presence of pair correlations are proposed. The pairing should also manifest itself via odd-even effects in cluster spectra, similar to the case of nuclei.