Single Dirac cone on the Cs-covered topological insulator surface Sb2Te3(0001)

Using angle-resolved photoelectron spectroscopy we investigate the surface electronic structure of the three-dimensional topological insulator (TI) Sb${}_{2}$Te${}_{3}$(0001). Our data show the presence of a topological surface state in the bulk energy gap with the Dirac point located above the Fermi level. The adsorption of Cs atoms on Sb${}_{2}$Te${}_{3}$(0001) gives rise to a downward energy shift of the electronic valence band states which saturates at a value of $\ensuremath{\sim}$200 meV. For the saturation coverage the Dirac point of the linearly dispersive surface state resides in close proximity to the Fermi level. The electronic structure of the Cs/Sb${}_{2}$Te${}_{3}$ interface therefore considerably deviates from previously studied metal-TI interfaces based on the isostructural compound Bi${}_{2}$Se${}_{3}$ which points to the importance of atomic composition in these hetero systems.