From orbital to paramagnetic pair breaking in layered superconductor 2H-NbS2

The superconducting transition-metal dichalcogenides 2H-NbSe2 and 2H-NbS2 are intensively studied on account of their unique electronic properties such as Ising superconductivity, found in multi-and monolayers, with upper critical fields beyond the Pauli limit. Even in bulk crystals, there are reports of multiband superconductivity and exotic states, such as the Fulde-Ferrell-Larkin-Ovchinnikov phase. In this work, we investigate the superconducting properties of 2H-NbS2 through a detailed high-field mapping of the phase diagram by means of magnetotransport and magnetostriction experiments. We compare the phase diagram between bulk crystals and a 6-nm-Thick flake of 2H-NbS2 and find a drastically enhanced Maki parameter in the flake, signifying a change of the relevant pair-breaking mechanism from orbital to paramagnetic pair breaking, which we attribute to an effect of enhanced spin-orbit coupling.