Observation of a topological phase transition in random coaxial cable structures with chiral symmetry

We report an experimental study of the disordered Su-Schrieffer-Heeger (SSH) model, implemented in a system of coaxial cables, whose radio frequency properties map onto the SSH Hamiltonian. By measuring multiple chains with random hopping terms, we demonstrate the presence of a topologically protected state, with frequency variation of less than 0.2% over the ensemble, evidence of near-perfect chiral symmetry. When the ends of the chains are connected to form loops, we observe a topological phase transition, characterized by the closure of the band gap and the appearance of states that are delocalized, despite the strong disorder.