  Interacting disordered zigzag graphene nanoribbons have fractional charges,
are quasi-one-dimensional, and display an exponentially small gap. Our
numerical computations showed that the topological entanglement entropy of
these systems has a small finite but universal value, independent of the
strength of the interaction and the disorder. The result that was obtained for
the topological entanglement entropy shows that the disorder-free phase is
critical and becomes unstable in the presence of disorder.
