In-plane magnetic penetration depth in NbS$_{2}$

TL;DR

This study investigates the temperature dependence of the in-plane magnetic penetration depth in NbS₂, revealing a fully open superconducting gap with evidence of two-gap superconductivity similar to NbSe₂, despite the absence of a charge density wave.

Contribution

It provides the first detailed measurement of the in-plane penetration depth in NbS₂, demonstrating two-gap superconductivity and comparing it to NbSe₂, highlighting the role of Nb tubular sheets.

Findings

Exponential temperature dependence of λ_ab indicating a fully open gap.

Presence of two superconducting gaps with different magnitudes.

Superconducting gaps are similar in NbS₂ and NbSe₂, independent of CDW presence.

Abstract

We report on the temperature dependence of the in plane magnetic penetration depth ($\lambda_{ab}$) and first penetration field ($H_f\propto 1/\lambda_{ab}^2(T)$ for $H\|c$) in 2H-NbS$_2$ single crystals. An exponential temperature dependence is clearly observed in $\lambda_{ab}$(T) at low temperature, signing the presence of a fully open superconducting gap. This compound is the only superconducting 2H-dichalcogenide which does not develop a charge density wave (CDW). However as previously observed in 2H-NbSe$_2$, this gap ($\Delta_{1}=1.1\, k_{B}T_{c}$) is significantly smaller than the standard BCS weak coupling value. At higher temperature, a larger gap ($\Delta_{2}=1.8\, k_{B}T_{c}$) has to be introduced to describe the data which are compatible with a two gap model. The superconducting gaps are hence very similar in NbS$_2$ and NbSe$_2$ and we show here that both of them open in the strongly coupled Nb tubular sheets independently of the presence of a CDW or not.