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

摘要

Topological insulators are a novel materials platform with high applicationspotential in fields ranging from spintronics to quantum computation. In theongoing scientific effort to demonstrate controlled manipulation of theirelectronic structure by external means, stoichiometric variation and surfacedecoration are two effective approaches that have been followed. In ARPESexperiments, both approaches are seen to lead to electronic band structurechanges. Such approaches result in variations of the energy position of bulkand surface-related features and the creation of two-dimensional electrongases.The data presented here demonstrate that a third manipulation handle isaccessible by utilizing the amount of illumination a topological insulatorsurface has been exposed to under typical experimental ARPES conditions. Ourresults show that this new, third, knob acts on an equal footing withstoichiometry and surface decoration as a modifier of the electronic bandstructure, and that it is in continuous competition with the latter. The dataclearly point towards surface photovoltage and photo-induced desorption as thephysical phenomena behind modifications of the electronic band structure underexposure to high-flux photons. We show that the interplay of these phenomenacan minimize and even eliminate the adsorbate-related surface band bending ontypical binary, ternary and quaternary Bi-based topological insulators.Including the influence of the sample temperature, these data set up aframework for the external control of the electronic band structure intopological insulator compounds in an ARPES setting. Four external knobs areavailable: bulk stoichiometry, surface decoration, temperature and photonexposure. These knobs can be used in conjunction to tune the band energies nearthe surface and consequently influence the topological properties of therelevant electronic states.