Disentangling orbital and spin characteristics of surface-derived states in Dirac nodal line semimetals

In this work, we explore surface states of nonsymmorphic semimetals with lifted band degeneracy at the symmetry points. HfSiS, a typical Dirac nodal-line semimetal with the nonsymmorphic symmetry exhibits a Rashba-type spin-split surface state. In this regard, we explore the Rashaba surface states which draw an analogy to the topological materials, where the spin and orbital entanglement takes place. We have performed spin- and angle-resolved photoemission spectroscopy experiment on HfSiS and ZrSiS single crystals with p-polarized and s-polarized light. The observed variation in the intensity distribution upon changing the light polarization tells us that the surface states along the M-X-M line are mainly composed of dz² orbitals, and change into d_yz along the G-X-G line. Combining the observed spin polarizations with the result of the slab calculation, we have concluded that the surface bands surrounding the X point exhibit a quite anisotropic spin and orbital texture. Our findings provide a new way of light manipulation by controlling the spin structure in materials which is important for future applications.