Dirac states with knobs on: interplay of external parameters and the surface electronic properties of 3D topological insulators

TL;DR

This study reveals that photon exposure during ARPES experiments can be used as a controllable external parameter to modify the electronic band structure of topological insulators, alongside stoichiometry, surface decoration, and temperature.

Contribution

It introduces photon exposure as a new, effective knob for tuning the surface electronic properties of topological insulators in ARPES experiments, demonstrating its competition with traditional methods.

Findings

Photon exposure affects electronic band structure similarly to stoichiometry and surface decoration.

Surface photovoltage and photo-induced desorption are key physical mechanisms behind band modifications.

External parameters can be combined to precisely control topological surface states.

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, stoichiometric variation and surface decoration are two effective approaches that have been followed. In ARPES experiments, both approaches are seen to lead to electronic band structure changes. 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 illumination a topological insulator surface has been exposed to under typical experimental ARPES conditions. Our results show that this new, 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 competition with the latter. The data clearly point towards surface photovoltage and photo-induced 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 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 tune the band energies near the surface and consequently influence the topological properties of the relevant electronic states.