Fig. 4: Nd4Te8Cl4O20, a Type-IV TMDI candidate.
From: Magnetic wallpaper Dirac fermions and topological magnetic Dirac insulators
a, b Crystal structures of NdTe2ClO5 and Nd4Te8Cl4O20 (2 × 2 × 1 supercell). c Magnetic structure compatible with Type-IV MSG 129.421 PC4/nmm and (001)-surface MWG \({p}_{c}^{{\prime} }4mm\). d Bulk band structure from DFT+U calculations (U = 6 eV). The band gap near the Fermi level is indicated by the red dashed line. e, f (001)-surface spectra for the e top (O-terminated) and f bottom (Nd-terminated) surfaces obtained using the surface Green’s function method. The surface Dirac fermion is indicated by the white arrow in e. g kz-directed Wilson loop spectrum along the diagonal path \(\overline{\Gamma }\)-\(\overline{M}\)-\(\overline{{\Gamma }^{{\prime} }}\). The winding structure exhibits \({{{{\mathcal{C}}}}}_{m}^{x\overline{y}}=-1\). h–i (001)-surface for the h top and i bottom surfaces from a 30-layer slab calculation. Bulk and surface bands are represented by gray and black, respectively. The fourfold-degenerate Dirac fermions are located approximately 1 eV from the Fermi level on the top surface. A surface potential of −0.544 eV is introduced to push the Dirac point on the bottom surface into the gap.
