  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.
