Evolution of superconductivity in ultrathin NbS2

TL;DR

This study investigates how the superconductivity of ultrathin NbS2 layers diminishes with decreasing thickness, highlighting the roles of disorder, oxidation, and encapsulation in preserving superconducting properties.

Contribution

It provides a detailed analysis of the thickness-dependent superconductivity in NbS2 and demonstrates how encapsulation can maintain superconductivity in ultrathin layers.

Findings

Superconducting transition temperature decreases with reduced thickness.

Atmospheric oxygen causes chemical changes leading to loss of superconductivity.

Encapsulation with PMMA preserves superconductivity in ultrathin NbS2.

Abstract

We report a systematic study of thickness-dependent superconductivity and carrier transport properties in exfoliated layered 2H-NbS2. Hall-effect measurements reveal 2H-NbS2 in its normal state to be a p-type metal with hole mobility of 1-3 cm2/Vs. The superconducting transition temperature is found to decrease with thickness. We find that the suppression of superconductivity is due to disorder resulting from the incorporation of atmospheric oxygen and a reduced hole density. Cross-section transmission electron microscope (TEM) imaging reveals a chemical change of NbS2 in ambient conditions, resulting in the formation of amorphous oxide layers sandwiching crystalline layered NbS2. Though few-nm-thick 2H-NbS2 completely converts to amorphous oxide in ambient conditions, PMMA encapsulation prevents further chemical change and preserves superconductivity.