Size and Impurity Effects on Scattering of Valley Hall Modes in Gate-Defined Bilayer Graphene Superlattices

Abstract: In the present paper we perform a tight-binding simulation of gate-defined islands in Bernal bilayer graphene (BLG). The inversion of the gap sign on the boundaries of the islands creates topologically-protected valley Hall modes. We focus on the specific questions of whether the valley Hall modes around such islands could serve as a host for quantum walks or simulate weakly coupled systems, and how their tunneling is affected by in-gap impurities. In addition, we discuss the effect of misalignment of top and bottom gate patterns on the tunneling properties between islands. Our main results show that resonant tunneling via an impurity enhances overlap between superlattice islands, while misalignment does not break topological protection over a wide parameter regime. In addition, we study the two-island geometry and show that it is possible to leverage suppressed scattering to place islands more densely on a single sample.