Symmetry breaking is identified as a predominant mechanism governing the formation of exotic quantum state. The absence of inversion symmetry in noncentrosymmetric superconductors leads to an antisymmetric spin-orbit coupling, which promotes the system toward possible unconventional electron pairings. In this work, we present angle-resolved magnetotransport measurements on noncentrosymmetric $4H_{\mathrm{a}}\text{-NbS}{\mathrm{e}}_2$ single crystal with $T_{\mathrm{CDW}}\sim 40\mathrm{K}$ and $T_{\mathrm{c}}\sim 6.4\mathrm{K}$, to further shed light on the underlying mechanisms responsible for the Pauli-limit-violated and in-plane anisotropic superconductivity in transition metal dichalcogenides. Our results reveal that the broken inversion symmetry generates Zeeman-like spin-orbit coupling which induces spin-momentum locking. As a result, the in-plane upper critical field exceeds the Pauli limit, which evidences the existence of an Ising pairing state. We surprisingly note that upper critical field manifests a distinct twofold modulation when the magnetic field is rotated in the basal plane. The twofold symmetric superconductivity spontaneously breaks the threefold rotational symmetry of the crystal lattice, indicating nematic superconductivity in this bulk Ising superconductor.

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• Superconductivity
• Transition metal dichalcogenides
• First-principles calculations
• Resistivity measurements