title: Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films.
abstract: The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi(3+) in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the low-doping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state.
authors.affiliation: Magnetic Spectroscopy Group, Diamond Light Source, Didcot, OX11 0DE, United Kingdom.
authors.forename: A I
authors.initials: AI
authors.lastname: Figueroa
authors.affiliation: Magnetic Spectroscopy Group, Diamond Light Source, Didcot, OX11 0DE, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: van der Laan
authors.affiliation: Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, United Kingdom.|Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Harrison
authors.affiliation: Diamond Light Source, Didcot, OX11 0DE, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: Cibin
authors.affiliation: Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, United Kingdom.|Diamond Light Source, Didcot, OX11 0DE, United Kingdom.
authors.forename: T
authors.initials: T
authors.lastname: Hesjedal