|FIELD||Phys:Condensed Matter Physics|
|DATE||June 13 (Thu), 2019|
|SPEAKER||Dr. Moon Jip Park|
|TITLE||Higher order topology in twisted bilayer graphene|
Higher order topological insulators are newly proposed topological phases of matter, whose bulk topology manifests as localized modes on two or higher dimensional lower boundaries. In this talk, we propose that all large commensurate angle twisted bilayer graphene are genuine higher order topological insulator, hosting topological corner charges. In the large angles, the finite intervalley scattering breaks valley U(1) symmetry and opens up the bulk gap. Within this gap, we show that the corner states occur at half-filling. We support our argument by presenting the first principle DFT calculation at the largest commensurate angle as an example. In addition, we generally prove that the corner states emerge regardless of the microscopic details of the interlayer coupling or the choice of the specific angles as long as the underlying symmetries are intact.