We report the formation of a bilayer Bi(111) ultrathin film, which is theoretically predicted to be in a two-dimensional quantum spin Hall state, on a Bi(2)Te(3) substrate. From angle-resolved photoemission spectroscopy measurements and ab initio calculations, the electronic structure of the system can be understood as an overlap of the band dispersions of bilayer Bi and Bi(2)Te(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.

No abstract

No abstract

No abstract

We have performed in situ spin-and angle-resolved photoemission and ex situ magnetotransport measurements on ultrathin topological insulator Bi 2 Se 3 films. The surface states deviate from a simple isotropic Dirac fermion due to hexagonal warping effects and their spin helical nature has been verified. In addition, the bulk states also cross the Fermi level, showing that the films are actually n doped. However, the temperature dependence of the film resistivity was insulating and saturated below 35 K. Furthermore, the magnetoresistivity changed drastically as the sample was cooled down and showed an anomaly near zero field below 20 K. The possible origin of this peculiar behavior and the nature of the carriers involved are discussed in comparison with the results for nonmetallic bulk samples.