Noncentrosymmetric superconductors, characterized by broken inversion symmetry, represent a distinctive subclass of unconventional superconductors. Here, we report the growth of single crystals of a noncentrosymmetric superconductor $h$-NbS, and systematical characterization of crystal structure and superconducting properties. Different from $o$-NbS, $h$-NbS crystallizes in a NiAs-type hexagonal superstructure with site-selective Nb vacancies. First-principles calculations reveal that the $\mathrm{Nb}\text{−}4d$ states dominate at the Fermi level ($E_{\mathrm{F}}$), with the density of states near $E_{\mathrm{F}}$ manifesting significant sensitivity to the concentration of the Nb vacancies. Nodeless moderately coupled two-gap superconductivity with a critical temperature of 2.6 K is confirmed in this strong type-II superconductor. The anisotropic parameters based on upper and lower critical fields have small values of $\sim 1.4$ and $\sim 1.3$, respectively, which demonstrate that the Cooper pairs show almost isotropic resilience to magnetic field. We surprisingly note that the upper critical field along the $ab$ plane surpasses the Pauli limit, largely arising from the two-dimensional Fermi-surface sheet around the K and H points of the Brillouin zone, which is related to the breaking of inversion symmetry. In contrast to quasi-one-dimensional and quasi-two-dimensional Nb-chalcogenide superconductors, the three-dimensional $h$-NbS featuring Pauli-limit violation provides a unique material for investigating unconventional superconductivity.

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• Superconductivity
• Chalcogenides
• Single crystal materials
• Crystal growth
• First-principles calculations
• Magnetization measurements
• Resistivity measurements
• Specific heat measurements
• X-ray diffraction