Layer-locked spin states revealed in the centrosymmetric nodal-line semimetal HfSiS

The spin-polarized bulk states in the centrosymmetric nodal-line semimetal HfSiS were observed by spin- and angle-resolved photoelectron spectroscopy. Combining with density functional theory calculations and the tight-binding model, the layer-locked spin states' nature of the observed $\mathrm{\ensuremath{\Lambda}}$-shaped bulk bands was revealed and the tight-binding model shows the importance of the next-nearest-neighbor term of spin-orbit coupling in the spin reversal of the bands along the $\overline{\mathrm{\ensuremath{\Gamma}}}\text{\ensuremath{-}}\overline{\mathit{M}}$ direction. Furthermore, the topological essence of attractive Dirac node arc states was confirmed.