Intra- and interband electron scattering in a hybrid topological insulator: Bismuth bilayer onBi2Se3

Abstract

The band structure and intra- and interband scattering processes of the electrons at the surface of a bismuth bilayer on ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ have been experimentally investigated by low-temperature Fourier-transform scanning tunneling spectroscopy. The observed complex quasiparticle interference patterns are compared to a simulation based on the spin-dependent joint density of states approach using the surface-localized spectral function calculated from first principles as the only input. Thereby, the origin of the quasiparticle interferences can be traced back to intraband scattering in the bismuth-bilayer valence band and ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ conduction band and to interband scattering between the two-dimensional topological state and the bismuth-bilayer valence band. The investigation reveals that the bilayer band gap, which is predicted to host one-dimensional topological states at the edges of the bilayer, is pushed several hundred meV above the Fermi level. This result is rationalized by an electron transfer from the bilayer to ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ which also leads to a two-dimensional electron state in the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ conduction band with a strong Rashba spin splitting, coexisting with the topological state and bilayer valence band.