Fig. 2: Two-band Su-Schrieffer-Heeger (SSH) model.
a Non-Hermitian SSH model with non-reciprocal inter-unit-cell hopping. Intra-unit-cell hoppings are d and inter-unit-cell hoppings are teθ and te−θ. The dashed box denotes the unit cell. b Phase diagrams of the non-Hermitian SSH model. The black dot denotes a Dirac point, and the curved lines denote EPs. The 12 regime (I) is a trivial line-gapped regime of two trivial 1-cycle bands, the \({\bar{2}}^{1}\) regime (II) is a point-gapped regime of a 2-cycle non-separable band with a π Zak phase, and the \({\bar{1}}^{2}\) regime (III) is a line-gapped regime of two 1-cycle bands with π Zak phases. c The connection between the Zak phase of the one-dimensional SSH model and the EPs in parameter space, (t,k) space. Black, blue, and red paths respectively contain zero, one, and two EPs in (t,k) space, which correspond to 12, \({\bar{2}}^{1}\), and \({\bar{1}}^{2}\) phases.
