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.

Electronic and spin structure of the topological insulator Bi2Te2.4Se0.6

“…Similarly, in Ref. [21], the position of the Dirac point for Bi 2 A shift of the Dirac point toward higher binding energies and the appearance of the occupied states near the bottom of the bulk conduction band are typically observed for BiTe-Se topological compounds even at cryogenic temperatures [29][30][31]. In these works, the observed states appeared around the bottom of the conduction band and below the upper edge of the surface-projected valence band gap.…”

“…In addition to these states, quantized Rashba-type states below the conduction band bottom (inside the bulk band gap) and M-shaped states inside the valence band local gap can arise as a result of adsorption of residual gases and of a variety other species. Such states can be formed due to confinement of the bulk conduction and valence band states in a quantum well which develops in a thin surface layer if band bending produced by adsorption [29][30][31] or intercalation of adsorbates into the van der Waals spacings [32,33] are significant.…”

Photoemission ofBi2Se3with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?

“…In spite of the considerable success of SR ARPES, it has been recently challenged by other experimental [11,12] and theoretical [13,14] proposals regarding both the efficiency and the reliability of the SR-ARPES measurements in studying the spin properties of TI surfaces. Part of these proposals involves the interpretation of the circular dichroism in the angular distribution (CDAD) of ARPES as the spin polarization of TSSs [11][12][13], which, if correct, can significantly improve the efficiency of spin detection.…”

Momentum and photon energy dependence of the circular dichroic photoemission in the bulk Rashba semiconductorsBiTeX(X=I, Br, Cl)

“…However, there is no general * alberto.crepaldi@elettra.eu consensus about the physical mechanism at the origin of the dichroism in CD-ARPES experiments. Recent theoretical and experimental studies proposed to interpret the dichroism in giant spin-split states in surface alloys [17][18][19] and in TIs [20][21][22][23] as the result of local orbital angular momentum (OAM [17,18,21,(24)(25)(26)) or directly as a measure of the spin polarization [20].Recently, a large variation of the dichroism as a function of the incoming photon energy as well as the change in its sign have been reported by Scholz and co-workers for the topological insulator Bi 2 Te 3 [27]. A similar observation was reported for the TI Bi 2 Te 2 Se by Neupane et al [28].…”