Upper panels: the Haldane model (b). The red (blue) circles represent the sublattices with on-site energy m (- m) and the black lines indicate the nearest-neighbor couplings with strength t. The Orange arrows in (b) indicate the next-nearest-neighbor (NNN) couplings t2 e i phi (t2 e - i phi) along (opposite to) the arrow. Lower panels: Schematics of the Dirac cone dispersion of the Haldane model (b). For the Haldane model, the TRS breaking leads to a single Dirac cone in the K valley in the energy range within the bandgap of the K' valley, as denoted by the orange dashed lines.
