Superconducting properties and Hall Effect of epitaxial NbN thin films

TL;DR

This study investigates how the superconducting transition temperature and Hall effect in epitaxial NbN thin films are influenced by growth conditions, revealing that carrier density primarily governs superconductivity rather than disorder.

Contribution

It demonstrates that tuning carrier density during growth affects superconducting properties, providing insights into the interplay between carrier density and disorder in NbN films.

Findings

Carrier density varies significantly with growth conditions.

Superconducting transition temperature correlates with carrier density.

Carrier mobility remains relatively stable across samples.

Abstract

We have measured the magnetotransport properties and Hall effect of a series of epitaxial NbN films grown on (100) oriented single crystalline MgO substrate under different conditions using reactive magnetron sputtering. Hall effect measurements reveal that the carrier density in NbN thin films is sensitive to the growth condition. The carrier density increases by a factor of 3 between the film with highest normal state resistivity (rho_n~3.83micro-Ohm-m) and lowest transition temperature (Tc~9.99K) and the film with lowest normal state resistivity (rho_n~0.94micro-Ohm-m) and highest transition temperature (Tc~16.11K) while the mobility of carriers does not change significantly except for the most resistive films. Our results show that the Tc of NbN is governed primarily by the carrier density rather than disorder scattering. By varying the carrier concentration during growth we can vary the effective disorder (kF_l) from the moderately clean limit to the dirty limit which makes this system ideal to study the interplay of carrier density and disorder on the superconducting properties of an s-wave superconductor.