title: Emergent quantum confinement at topological insulator surfaces.
abstract: Bismuth-chalchogenides are model examples of three-dimensional topological insulators. Their ideal bulk-truncated surface hosts a single spin-helical surface state, which is the simplest possible surface electronic structure allowed by their non-trivial Z(2) topology. However, real surfaces of such compounds, even if kept in ultra-high vacuum, rapidly develop a much more complex electronic structure whose origin and properties have proved controversial. Here we demonstrate that a conceptually simple model, implementing a semiconductor-like band bending in a parameter-free tight-binding supercell calculation, can quantitatively explain the entire measured hierarchy of electronic states. In combination with circular dichroism in angle-resolved photoemission experiments, we further uncover a rich three-dimensional spin texture of this surface electronic system, resulting from the non-trivial topology of the bulk band structure. Moreover, our study sheds new light on the surface-bulk connectivity in topological insulators, and reveals how this is modified by quantum confinement.
authors.affiliation: Correlated Electron Research Group, RIKEN-ASI, Wako, Saitama 351-0198, Japan.
authors.forename: M S
authors.initials: MS
authors.lastname: Bahramy
authors.forename: P D C
authors.initials: PD
authors.lastname: King
authors.forename: A
authors.initials: A
authors.lastname: de la Torre
authors.forename: J
authors.initials: J
authors.lastname: Chang
authors.forename: M
authors.initials: M
authors.lastname: Shi
authors.forename: L
authors.initials: L
authors.lastname: Patthey
authors.forename: G
authors.initials: G
authors.lastname: Balakrishnan
authors.forename: Ph
authors.initials: P
authors.lastname: Hofmann
authors.forename: R
authors.initials: R
authors.lastname: Arita
authors.forename: N
authors.initials: N
authors.lastname: Nagaosa
authors.forename: F
authors.initials: F
authors.lastname: Baumberger