SSH chain: bulk band gap and topologically protected edge modes
The Su-Schrieffer-Heeger (SSH) model is a 1D tight-binding chain with alternating hoppings v (intracell) and w (intercell). The bulk winding number Z = 0 when |v| > |w| (trivial) and Z = 1 when |w| > |v| (topological), with in-gap edge states at E=0. This is the simplest model realizing the bulk-boundary correspondence, a cornerstone of topological band theory.