Broken screw rotational symmetry in the near-surface electronic structure of nodal line materials

Nonsymmorphic symmetries, such as screw rotations and glide reflections, can induce characteristic nodal lines or surfaces in the band dispersions of crystals. However, since the nonsymmorphic symmetries responsible for the formation of the nodal lines may not be maintained in the surface region, the crystal surface may host a different electronic structure from the bulk.

In this presentation, we present an extensive ARPES study of the differences between the near-surface electronic structure and the bulk structure hosting nodal lines. Due to electron scattering processes, ARPES can only capture the near-surface electronic structure of a crystal up to a depth of a few nanometers from the surface. We examine the near-surface electronic structure of $AB$-stacked $2H$-$mathrm{Nb}mathrm{S}_2$ and $h$BN crystals, both of which host bulk nodal lines on the $k_z=pi/c$ plane. We found gapped band dispersions on the $k_z=pi/c$ plane, indicating that the broken screw rotational symmetry at the surface opens an energy gap in the near-surface electronic structure. Taking into account the surface sensitivity of ARPES, our photoemission intensity calculations [1] could reproduce such gapped spectra by adjusting the probing depth parameter in the simulation. Our results show that incomplete nonsymmorphic symmetries can alter the near-surface electronic structure associated with the bulk nodal lines [2].