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

Abstract

Topological insulators are a novel materials platform with high applications potential in fields ranging from spintronics to quantum computation. In the ongoing scientific effort to demonstrate controlled manipulation of their electronic structure by external means, i.e., the provision of knobs with which to tune properties, stoichiometric variation and surface decoration are two effective approaches that have been followed. In angleresolved photoelectron spectroscopy (ARPES) experiments, both approaches are seen to lead to electronic band-structure changes. Most importantly, such approaches result in variations of the energy position of bulk and surface-related features and the creation of two-dimensional electron gases. The data presented here demonstrate that a third manipulation handle is accessible by utilizing the amount of super-band-gap light a topological insulator surface has been exposed to under typical ARPES experimental conditions. Our results show that this third knob acts on an equal footing with stoichiometry and surface decoration as a modifier of the electronic band structure, and that it is in continuous and direct competition with the latter. The data clearly point towards surface photovoltage and photoinduced desorption as the physical phenomena behind modifications of the electronic band structure under exposure to high-flux photons. We show that the interplay of these phenomena can minimize and even eliminate the adsorbate-related surface band bending on typical binary, ternary, and quaternary Bi-based topological insulators. Including the influence of the sample temperature, these data set up a detailed framework for the external control of the electronic band structure in topological insulator compounds in an ARPES setting. Four external knobs are available: bulk stoichiometry, surface decoration, temperature, and photon exposure. These knobs can be used in conjunction to fine tune the band energies near the surface and consequently influence the topological properties of the relevant electronic states.

Angle-resolved and core-level photoemission study of interfacing the topological insulatorBi1.5Sb0.5Te1.7Se1.3with Ag,

“…2(e)]. This is of fundamental interest as the conduction band of BSTS becomes occupied with electrons at the surface simply following a few hours of exposure to UHV [37,38].…”

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.…”

“…We conclude that our analysis of the LL plot including the parabolic energy term and Zeeman term is in agreement with topological surface state. Although we did not make a similar full analysis of the LL plot for (x, y) = (0.54, 1.3) starting from ARPES data, we note that minor changes in bulk stoichiometry do not affect the ARPES spectra of BSTS [35].…”

Metal-insulator transition and tunable Dirac-cone surface state in the topological insulatorTlBi1−xSbxTe2studied by angle-resolved photoemission

“…In addition, as mentioned above, the surface chemical potential of TBST was found to be robust against surface aging. This situation is different from BSTS [13] and prototypical TIs [37], where the surface chemical potential is sensitive to small perturbations such as the gas adsorption on the surface, pointing to a good surface controllability in TBST, which is a prerequisite for realistic applications.…”