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Persistence of chirality in the Su-Schrieffer-Heeger model in the presence of on-site disorder

We consider the effects of on-site and hopping disorder on zero modes in the Su-Schrieffer-Heeger model. In the absence of disorder a domain wall gives rise to two chiral fractionalized bound states, one at the edge and one bound to the domain wall. On-site disorder breaks the chiral symmetry, in contrast to hopping disorder. By using the polarization we find that on-site disorder has little effect on the chiral nature of the bound states for weak to moderate disorder. We explore the behaviour of these bound states for strong disorder, contrasting on-site and hopping disorder and connect our results to the localization properties of the bound states and to recent experiments.