In-plane magnetic penetration depth in NbS${}_2$

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$H|c$)in2H-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 (${\mathrm{\Delta }}_1=1.1k_B{T}_c$) 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.