Unconventional quantized edge transport in the presence of interedge coupling in intercalated graphene

It is generally believed that the interedge coupling destroys the quantum spin Hall (QSH) effect along with the gap opening at the Dirac points. Using first-principles calculations, we find that the quantized edge transport persists in the presence of interedge coupling in Ta intercalated epitaxial graphene on SiC(0001), being a QSH insulator with the nontrivial gap of 81 meV. In this case, the band is characterized by two perfect Dirac cones with different Fermi velocities, yet only one maintains the edge state feature. We attribute such an anomalous behavior to the orbital-dependent decay of edge states into the bulk, which allows the interedge coupling between just one pair of edge states rather than two.