Tuning the vertical location of helical surface states in topological insulator heterostructures via dual-proximity effects

Abstract

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.

Proximity-induced topological state in graphene

“…Notably, this feature resembles closely the one reported for the interface between the normal metal Sb 2 Se 3 and the TI Bi 2 Se 3 [25]. Also, the behavior is similar to the topologization of ZnM (M = S, Se, Te) upon deposition on Bi 2 Se 3 [7].…”

“…For instance, depositing normal semiconductors on top of 3D topological insulators may result in a structure that under certain conditions exhibits topologically protected interface states [7]. An even more attractive prospect is that of using that protocol for transferring topologically protected states to graphene [8,9].…”

Band bending driven evolution of the bound electron states at the interface between a three-dimensional topological insulator and a three-dimensional normal insulator

“…If the band-bending energy is not large, |lϕ 0 | Bq 0 1 , the Dirac-like gapless state appears with the node point distant from the middle of the bulk gap, E (2) (κ = 0) . The envelope function of this bound state indicated by N = 2 has a finite amplitude on either the TI or NI side of the interface, at that 2 (z = 0) ∼ (2) (z = 0).…”

“…[27,28], in density functional calculations (DFT), it was found that the K adatoms on ultrathin films of Bi 2 Se 3 induce downward band bending within 2 to 3 nm from the surface, due to charge transfer from the adatoms to the TI, which lead to a Dirac-cone state, localized slightly deep into the TI. There are now intensive experimental and theoretical efforts on studying the interface states in various 3D TI-based heterostructures that carry the signature of both topology and contact conditions [1][2][3][20][21][22][23]29,30]. Below we throw light on the role of the band-bending effect in the formation of the bound electron states at the TI/NI interface.…”

“…[1][2][3] and references therein). Such the interest is due to predicted unusual properties of the TI/NI heterostructures, but to utilize them in next-generation nanoelectronic devices, one should take an important step to drive the characteristics of interfacial electron states in the design of the TI/NI systems.…”