  We address the co-existence of massless and massive topological edge states
at the interface between two materials with different topological phases. We
modify the well known Bernevig-Hughes-Zhang model to introduce a smooth
function describing the band inversion and the band bending due to
electrostatic effects between the bulk of the quantum well and the vacuum.
Within this minimal model we identify distinct parameter sets that can lead to
the co-existence of the two types of edge states, and that determine their
number and characteristics. We propose several experimental setups that could
demonstrate their presence in two-dimensional topological systems, as well as
ways to regulate or tune the contribution of the massive edge states to the
conductance of associated electronic devices. Our results suggest that such
states may also be present in novel two-dimensional Van der Waals topological
materials.
