Tunable inter-scattering between counter-propagating quantum Hall edge channels in a topological insulator HgTe

Recent advances reveal that the surfaces of three-dimensional (3D) topological insulators can host massless (Dirac) and massive surface states. The surface of a 3D topological insulator is a closed 2D manifold. Therefore, the interplay of top and bottom surfaces is expected to be prominent via sides, especially as the edge states are predominant in quantum Hall regime. Here we demonstrate the formation of counter-propagating edge states, originating from opposite surfaces. Additionally, our measurements show that the counter-propagating edge states are intensively scattered into each other, evidenced by a deviation from the non-interscatering Landauer-Büttiker formalism. In this case, a scattering model helps to quantify the inter-scattering strength among counter-propagating edge states, which is later shown to be tuable by gate voltages and temperature. The modelling for muliple edge states suggests a selection rule of inter-scattering among edge states, which only allows for prominent inter-scattering between paried edge states with the same Landau index N. Our research provides a platform to further investigate the microscopic mechanism of interaction of edge channels in quantum Hall regime.