Role of the vortex-core energy on the Beresinkii-Kosterlitz-Thouless transition in thin films of NbN

TL;DR

This paper investigates how vortex-core energy influences the Berezinskii-Kosterlitz-Thouless transition in NbN thin films, highlighting its role in superfluid density and resistivity behavior near the transition.

Contribution

It demonstrates the crucial impact of vortex-core energy on BKT signatures and estimates its variation with disorder in NbN thin films.

Findings

Vortex-core energy significantly affects BKT transition signatures.

Disorder level influences vortex-core energy in NbN films.

Experimental data aligns with theoretical models of vortex fluctuations.

Abstract

We analyze the occurrence of the Beresinkii-Kosterlitz-Thouless transition in thin films of NbN at various film thickness, by probing the effect of vortex fluctuations on the temperature dependence of the superfluid density below $T_{BKT}$ and of the resistivity above $T_{BKT}$. By direct comparison between the experimental data and the theory we show the crucial role played by the vortex-core energy in determining the characteristic signatures of the BKT physics, and we estimate its dependence on the disorder level. Our work provides a paradigmatic example of BKT physics in a quasi-two-dimensional superconductor.