  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.
