Conductance fluctuations induced by bulk state in quasi-one-dimensional strips of topological insulator

We numerically calculate the conductance of a topological insulator confined as quasi-one-dimensional strips using a four-band Hamiltonian. The conductance is nearly unchanged in the presence of a short-range disorder when the Fermi level is located in the bulk band gap. Helical edge states of topological insulators are no longer protected against the disorder, and scattering takes place if the bulk state coexists. Both the magnitude of conductance fluctuations and the average conductance are found to vary nonmonotonically in the latter regime with the strength of disorder, where the fluctuation amplitude is reduced when the average conductance is around 2e(2)/h. The scattering of the topological states is hence evidenced to be nontrivially affected by the coupling with the bulk state.