Surface electronic structure of Bi2Te3(111) studied by high-resolution photoelectron spectroscopy using synchrotron radiation

We have investigated the surface electronic structure on vacuum-cleaved n- and p-type Bi2Te3(111) at 10 K by high-resolution photoelectron spectroscopy. The surface sensitivity was maximized by tuning photon energy using synchrotron radiation as an excitation source, probing the topmost two quintuple layers (QLs). The Bi 5d and Te 4d core levels are also observed in high energy resolution. The absence of surface core-level shift of Bi 5d clearly demonstrates that the topmost layer of the cleaved Bi2Te3(111) is composed of a Te layer. In the angle-resolved photoelectron spectra, the gapless surface-state bands (SSBs) as well as the bulk conduction and valence bands (BVBs) are clearly observed, ensuring the topological nature. The k(parallel to) dispersion of most of the BVBs along the (Gamma) over bar-(M) over bar line in the surface Brillouin zone is highly symmetrical around the (Gamma) over bar against the threefold symmetry of the crystal structure, where k(parallel to) is the wave vector parallel to the surface. The topmost Te layer of sixfold structure must dominantly contribute to the symmetrical k(parallel to) dispersion. Moreover, the BVBs show almost flat k(parallel to) dispersion, where k(parallel to) is the wave vector perpendicular to the surface. These observations are the direct experimental evidence of a strong modification of the valence bands within the topmost two QLs into strongly two-dimensional states by the advent of the surface. In conclusion, the surface electronic structure within the two QLs is composed of the SSBs and modified two-dimensional valence bands.