The electronic structure of clean and adsorbate-covered Bi₂Se₃: an angle-resolved photoemission study

Abstract

Angle-resolved photoelectron spectroscopy is used for a detailed study of the\nelectronic structure of the topological insulator Bi2Se3. Nominally\nstoichiometric and calcium-doped samples were investigated. The pristine\nsurface shows the topological surface state in the bulk band gap. As time\npasses, the Dirac point moves to higher binding energies, indicating an\nincreasingly strong downward bending of the bands near the surface. This\ntime-dependent band bending is related to a contamination of the surface and\ncan be accelerated by intentionally exposing the surface to carbon monoxide and\nother species. For a sufficiently strong band bending, additional states appear\nat the Fermi level. These are interpreted as quantised conduction band states.\nFor large band bendings, these states are found to undergo a strong Rashba\nsplitting. The formation of quantum well states is also observed for the\nvalence band states. Different interpretations of similar data are also\ndiscussed.\n