SSH Model — Topological Edge States

SSH model: A 1D chain with alternating hoppings v (intra-cell) and w (inter-cell). Topological phase: w > v gives winding number ν = 1, and two zero-energy edge states appear at the ends. Normal phase: w < v, ν = 0, no edge states. The bulk energy gap Δ = 2|v − w|. This is the simplest topological insulator — a model system for understanding topological protection.