  It is generally believed that the inter-edge 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 inter-edge coupling in Ta intercalated epitaxial
graphene on SiC(0001), being a QSH insulator with the non-trivial 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 inter-edge coupling just between one
pair of edge states rather than two.
