Micro-metric electronic patterning of a topological band structure using a photon beam

Abstract

In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi2−xSbxTe3−ySey with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi2−xSbxTe3−ySey crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by ‘writing’ micron-sized letters in the Dirac point energy of the system.

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

“…At such locations, the BB is now strong enough to act as a potential well and clear signatures of confinement are then observed in the conduction and valence bands [19,20,32]. The observation that unexposed areas are different reveals a degree of local character in the photon-induced changes on Bi 2 Se 3 , which is dramatically enhanced for bulk-insulating quaternary TI compounds [52].…”

“…This effect has been modeled in Ref. [52], and exploited to create micro-metric patterns in the topological band structure.…”

“…This interaction leads to a decrease of the Dirac point binding energy, the energy value of which can be tuned via choice of the photon flux, energy, and exposure time. This second knob operates at a local spatial level [52].…”

Comparative study of rare earth hexaborides using high resolution angle-resolved photoemission

“…51, 52). Our earlier ARPES study on YbB 6 [34] has reported a pronounced time dependent energy shift of these low-lying occupied states towards the unoccupied part of the spectrum, which may be attributed to changes to the initial surface band bending due to the effect of the photon beam and/or changes in adsorption at the surface [53][54][55].…”

Quantum oscillations of the topological surface states in low carrier concentration crystals of Bi2−xSbxTe3Pan1, Никитин2, Wu3 et al. 2016Solid State CommunicationsSelf Cite7100View full textAdd to dashboardCite

“…In order to fit the energy dispersion of the topological surface state as accurately as possible we need to maximize the number of data points in the occupied part of the energy spectrum. In this sense, the time-dependent energy shift to lower energies observed in BSTS [35,36] and other Bi-based TIs [37,38] is beneficial. We therefore chose to fit data acquired on a sample which has been maintained for 8 h in a background pressure in the mid 10 −11 mbar range.…”