Interfacing 2D and 3D Topological Insulators: Bi(111) Bilayer on Bi$_2$Te$_3$

Topological insulators (TI) are insulating materials but have metallic edge states that carry spin currents and are robust against nonmagnetic impurities [1]. While there have been a large number of reports on three-dimensional (3D) TI, only few works have been done in terms of two-dimensional (2D) TI. In the present paper, we report the successful formation of bilayer Bi, which was theoretically predicted to be a 2D TI [2]. We deposited bilayer Bi on a 3D TI $\mathrm{Bi_2Te_3}$, which the lattice mismatch is very small. From angle-resolved photoemission spectroscopy measurements and {\it ab initio} calculations, the electronic structure of the system can be understood as an overlap of the band dispersions of bilayer Bi and $\mathrm{Bi_2Te_3}$. Our results show that the Dirac cone is actually robust against nonmagnetic perturbations and imply a unique situation where the topologically protected one- and two-dimensional edge states are coexisting at the surface [3]. \\[0pt] [1] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. {\bf 82}, 3045 (2010).\\[0pt] [2] S. Murakami, Phys. Rev. Lett. {\bf 97}, 236805 (2006).\\[0pt] [3] T. Hirahara {\it et al.,} Phys. Rev. Lett. {\bf 107}, 166801 (2011).