Symmetry-enforced electronic nodal straight lines in CsNb3SBr7

We propose the quaternary-compounds CsNb3SBr7 is a nodal-straight-line semimetal candidate based on the first-principles calculations and symmetry analyses. There are a pair of nodal straight lines locate in the k ( z ) = 0 plane of Brillouin zone, which is protected by the crystal symmetry. The topological properties of nodal-straight-line state are characterized by the nontrivial Berry phase and Berry curvature. On the (001) surface of CsNb3SBr7, Fermi arcs form the belt-like surface state, connecting the nodal straight lines with opposite chirality. Furthermore, the Hofstadter's butterfly and optical conductivity are investigated using a slab sample. These results not only reveal the symmetric protection mechanism of nodal straight lines, but also pave a way for exploring the electronic and optical properties of CsNb3SBr7 in further condensed matter physics experiments.