Fig. 1: Lattice structure, band structure, and the Wilson loop spectrum.
From: Two-dimensional higher-order topology in monolayer graphdiyne
a A schematic figure describing the unit cell and the relevant atomic orbitals of a monolayer graphdiyne (MGD) composed of 18 carbon atoms. Two sublattices are marked with yellow and blue colors, respectively. Since MGD has a bipartite lattice structure, chiral symmetry exists when only the nearest neighbor hoppings are considered. b The band structure of MGD obtained by first-principles calculations, which shows approximate chiral symmetry near the Fermi level. Since pz orbitals are odd while s, px, py orbitals are even under the mirror Mz:z → −z operation, the energy spectrum from pz orbitals (blue) is not hybridized with that from s, px, py orbitals (red). c The Wilson loop spectrum computed including s, px, py, pz orbitals. The spectrum exhibits a crossing point at ky = 0, θ = π, which indicates w2 = 1.
