Fig. 1
From: Topological characterizations of an extended Su–Schrieffer–Heeger model
a The diagrammatic sketch of the SSH4 model. Tunneling terms are periodic with a unit cell of four sites. b The eigenenergy of each eigenstate for different γ with the SSH4 model for N = 6. tb = tc = td = 2π × 1 kHz, and ta varies. The red lines show that there are eigenstates with zero energy when 1/γ < 1, which correspond to the existence of topological edge states. When 1/γ > 1, there are no zero-energy eigenstates. For a large system (large N number), a sharp phase transition happens at γ = 1. c The probability amplitude and the population distribution for an edge state when 1/γ = 0.5, as circled in b
