Tuning the vertical location of helical surface states in topological   insulator heterostructures via dual-proximity effects
  In integrating topological insulators (TIs) with conventional materials, one crucial issue is how the topological surface states (TSS) will behave in such heterostructures. We use first-principles approaches to establish accurate tunability of the vertical location of the TSS via intriguing dual-proximity effects. By depositing a conventional insulator (CI) overlayer onto a TI substrate (Bi2Se3 or Bi2Te3), we demonstrate that, the TSS can float to the top of the CI film, or stay put at the CI/TI interface, or be pushed down deeper into the otherwise structurally homogeneous TI substrate. These contrasting behaviors imply a rich variety of possible quantum phase transitions in the hybrid systems, dictated by key material-specific properties of the CI. These discoveries lay the foundation for accurate manipulation of the real space properties of TSS in TI heterostructures of diverse technological significance. 
Guangfen Wu, Hua Chen, Yan Sun, Xiaoguang Li, Ping Cui, Cesare   Franchini, Jinlan Wang, Xing-Qiu Chen and Zhenyu Zhang
cond-mat.mtrl-sci