Photoemission-induced gating of topological insulators

Abstract

The recently discovered topological insulators exhibit topologically protected metallic surface states which are interesting from the fundamental point of view and could be useful for various applications if an appropriate electronic gating can be realized. Our photoemission study of Cu-intercalated Bi 2 Se 3 shows that the surface-state occupancy in this material can be tuned by changing the photon energy and understood as a photoemissioninduced gating effect. Our finding provides an effective tool to investigate the new physics coming from the topological surface states and suggests intercalation as a recipe for synthesis of a material suitable for electronic applications.

Dirac states with knobs on: Interplay of external parameters and the surface electronic properties of three-dimensional topological insulators

“…1(d) versus 1(e): greater for higher photon energy] does argue for a role for the SPV mechanism and is in keeping with a recent report on Bi 2 Se 3 [38].…”

“…By contrast to the plethora of studies following the two scenarios sketched above, only very few reports have been made regarding variations of the electronic band structure based on other external parameters such as temperature variations or exposure to continuous illumination [36,38].…”

“…SPVinduced charges accumulating at the surface of a semiconductor should lead to the deviation of the Fermi level from the equilibrium position [46], yet we do not observe this. This suggests that also for ternary and quaternary Bi-based 3D TIs the topological surface states are important in maintaining charge neutrality at the surface, as they have been argued to be in Bi 2 Se 3 [38]. A difference between the bulk-insulating systems and Bi 2 Se 3 (with its degenerate, defect-doped bulk) is that it is possible that photoinduced charges can be trapped locally in the subsurface region.…”

“…A difference between the bulk-insulating systems and Bi 2 Se 3 (with its degenerate, defect-doped bulk) is that it is possible that photoinduced charges can be trapped locally in the subsurface region. When swept apart by the in-built potential which gives rise to the downward band bending, these charges may therefore alter the energetics of the surface electronic structure in a manner somewhat analogous to a local back-gate, without the need for explicit surface charging and the requirement of a measurable shift of the Fermi level at the surface from the equilibrium position [38].…”

“…In particular, the last of these three factors has barely been addressed in the Bi 2 Se 3 ARPES literature: illumination effects have been considered in a single study that focused on hν-dependent changes [38].…”