Fig. 3. Orbital texture of flat bands and effective Wannier wave function.

a, c High-resolution band structure of CoSn along Γ–M and Γ–K–M high-symmetry directions, respectively. The data are measured with 128 eV photons, which probes band structure at k_z = 0 plane. b, d Corresponding DFT band structures. Cyan and orange lines, respectively, mark two flat bands arising from d_xz/d_yz and d_xy/d_x2 −y2 orbital degrees of freedom. Experimental dispersion of the flat bands (marked with orange and cyan arrows in a, c) are well reproduced by the calculation. The Dirac point at K are marked with white dots in c. e, f Orbital textures of the effective Wannier states constructed from the flat bands with d_xz/d_yz and d_xy/d_x2 −y2 orbitals, respectively. Length scale of the orbitals at each site is proportional to the orbital wave functions in the majority spin channel. Insets of e, f display the decay of total charge density (including the contribution from other orbitals) of the Wannier functions away from the central hexagon.