Size dependence of the Tc and the superconducting energy gap in nanocrystalline thin films of Nb

TL;DR

This study investigates how the superconducting transition temperature and energy gap in nanocrystalline Nb thin films vary with particle size, revealing size-dependent electronic effects without phonon softening.

Contribution

It demonstrates that size-dependent superconducting properties are governed by changes in electronic density of states rather than phonon softening in Nb films.

Findings

Tc decreases as particle size drops below 20 nm

Superconducting transition disappears below 8 nm

Size effects are linked to electronic density of states changes

Abstract

In nanocrystalline Nb films, the superconducting Tc decreases with a reduction in the average particle size below 20nm. We correlate the decrease in Tc with a reduction in the superconducting energy gap measured by point contact spectroscopy. Consistent with the Anderson criterion, no superconducting transition was observed for sizes below 8 nm. We show that the size-dependence of the superconducting properties in this intermediate coupling Type II superconductor is governed by changes in the electronic density of states rather than by phonon softening.