Spin-valley locking of the bulk transition-metal dichalocogenide superconductor NbSe$_{2}$

2H-NbSe$_{2}$ is a metallic transition metal dichalcogenide, which hosts instabilities to a charge density wave phase, and a superconducting phase at low temperatures [1]. To date, it has been assumed that these phases are largely unaffected by the spin degree of freedom. In contrast, from spin- and angle-resolved photoemission measurements, supported by first principles calculations, we reveal that the normal state Fermi surface hosts a complex spin texture. We uncover a rich spin-valley locking of the form also observed in the semiconducting materials of the same family [2], consistent with the recent observation of Ising pairing in the superconducting state of monolayer NbSe$_{2}$ [3]. We find that in the normal state of the bulk compound there is persistent spin polarisation which becomes intrinsically linked to the electronic dimensionality, showing a significant dependence on the out-of-plane momentum. This prompts a reinterpretation of the complex phases that emerge in this, and related materials. [1] Wilson JA et al, Phys. Rev. Lett. 32, 882 (1974). [2] Xiao D et al, Phys. Rev. Lett. 108, 196802 (2012); Xu X et al, Nature Phys. 10, 343–350 (2014); Riley JM et al, Nature Phys. 10, 835 (2014). [3] Xi X et al, arXiv:1507.08731.