Experimental observation of thermal fluctuations in single superconducting Pb nanoparticles through tunneling measurements

TL;DR

This study investigates how thermal fluctuations affect superconductivity in single Pb nanoparticles, revealing finite energy gaps above Tc and size-dependent energy gap reductions, supported by experimental and theoretical analysis.

Contribution

It provides the first detailed experimental and theoretical analysis of thermal fluctuation effects on superconductivity in zero-dimensional Pb nanoparticles.

Findings

Finite energy gap observed beyond Tc in particles smaller than 13nm.

Thermal fluctuations cause deviations from mean-field predictions.

Superconducting energy gap decreases with particle size below 20nm.

Abstract

An important question in the physics of superconducting nanostructures is the role of thermal fluctuations on superconductivity in the zero-dimensional limit. Here, we probe the evolution of superconductivity as a function of temperature and particle size in single, isolated Pb nanoparticles. Accurate determination of the size and shape of each nanoparticle makes our system a good model to quantitatively compare the experimental findings with theoretical predictions. In particular, we study the role of thermal fluctuations (TF) on the tunneling density of states (DOS) and the superconducting energy gap (D) in these nanoparticles. For the smallest particles, h < 13nm, we clearly observe a finite energy gap beyond Tc giving rise to a "critical region". We show explicitly through quantitative theoretical calculations that these deviations from mean-field predictions are caused by TF. Moreover, for T << Tc, where TF are negligible, and typical sizes below 20 nm, we show that D gradually decreases with reduction in particle size. This result is described by a theoretical model that includes finite size effects and zero temperature leading order corrections to the mean field formalism.