Persistence of surface states despite impurities in the surface of topological insulators

Abstract

PACS 73.20.-r -Electron states at surfaces and interfaces PACS 79.60.-i -Photoemission and photoelectron spectra PACS 71.20.-b -Electron density of states and band structure of crystalline solidsAbstract -We have experimentally demonstrated the robustness and immunity of the surface states to surface impurities and disorder in topological insulator (TI) Bi0.9Sb0.1 in comparison with those of semi-metallic Sb(111) surface by measuring the scattering rates of the quasiparticles (QP) via angle-resolved photoemission spectroscopy. The surface impurities on TIs increase the scattering rate of the QPs but their effects are extrinsic and limited regardless of their magnetic properties, while in the semimetallic Sb case they open new scattering channels making the surface states fragile.

Controlling the evolution of two-dimensional electron gas states at ametal/Bi2Se3interface

“…However, the development of the surface states does not originate from a topological property of TIs but from an interface property of metal/semiconductor. In the case of Bi 0.9 Sb 0.1 TI, our previous ARPES study shows just a small shift of the Fermi level in the electronic structure with response to the surface adsorption [11].…”

“…Since the discovery of topological insulators (TIs) with topologically protected metallic surface states [1][2][3][4][5][6], much attention has been paid to characterization of the topological surface states (TSSs), unveiling the abundant exotic properties of the TSSs such as the absence of back-scattering [7,8], the spin-momentum locking [6,9], the robustness against various kinds of surface perturbations [10][11][12][13]. In particular, the studies on the effect of surface adsorbates to the TSSs have found very intriguing phenomena that new Rashibatype spin-split surface states emerge on the (111) surface of Bi 2 Se 3 TI and that they have large amounts of common features irrespective of the electric/magnetic properties of the adsorbates [12,14,15].…”

Modification and Control of Topological Insulator Surface States Using Surface Disorder

“…Already many experiments have studied the effects on TI surfaces of disorder induced by atmosphere, by deliberate introduction of adsorbed molecules and dopants, and even by mechanical surface abrasion. [9][10][11][12][13][14][15][16][17][18] Numerous experiments have also demonstrated that capping can effectively protect a TI surface, so masking and etching techniques are promising, as is ion implantation. 19 Ion implantation in particular gives precise control of impurity concentration and depth, and allows control of the Fermi level by mixing ions.…”

Robust topological insulator conduction under strong boundary disorder

“…[8][9][10][11] However three recent angularly resolved photoemission spectroscopy (ARPES) experiments measured the surface band while progressively doping the TI surface with impurities and found that the surface signal becomes progressively fainter and more blurred as impurities are added. [12][13][14] Moreover several recent experiments have modified the TI surface by introducing an Al capping layer, or by gating the TI. 15,16 Another experiment reported that exposure to air causes growth of an oxide layer on top of the TI.…”

“…This is consistent with several experimental ARPES studies on 3-D TIs which saw the surface band signal weaken and blur as boundary disorder was increased. [12][13][14] Lastly at very large boundary disorder the in-gap states move just inside the disordered region and return to the Dirac dispersion found at weak disorder. Based on these numerical results, Schubert et al argued that when the disorder is larger than the gap the bulk and surface states mix, the Dirac cone is destroyed, and the TI surface states are no longer topologically protected.…”