Massive Dirac Fermion Observed in Lanthanide-Doped Topological Insulator Thin Films.
The breaking of time reversal symmetry (TRS) in three-dimensional (3D) topological insulators (TIs), and thus the opening of a 'Dirac-mass gap' in the linearly dispersed Dirac surface state, is a prerequisite for unlocking exotic physical states. Introducing ferromagnetic long-range order by transition metal doping has been shown to break TRS. Here, we present the study of lanthanide (Ln) doped Bi2Te3, where the magnetic doping with high-moment lanthanides promises large energy gaps. Using molecular beam epitaxy, single-crystalline, rhombohedral thin films with Ln concentrations of up to ~35%, substituting on Bi sites, were achieved for Dy, Gd, and Ho doping. Angle-resolved photoemission spectroscopy shows the characteristic Dirac cone for Gd and Ho doping. In contrast, for Dy doping above a critical doping concentration, a gap opening is observed via the decreased spectral intensity at the Dirac point, indicating a topological quantum phase transition persisting up to room-temperature.
Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, United Kingdom.|Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA.
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Harrison
Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, United Kingdom.
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Collins-McIntyre
Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, United Kingdom.
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Schönherr
Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA.
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Vailionis
Stuttgart Center for Electron Microscopy, Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart, Germany.
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Srot
Stuttgart Center for Electron Microscopy, Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart, Germany.
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van Aken
IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA.
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Kellock
IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA.
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Pushp
IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA.
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Parkin
Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA.
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Harris
Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, United Kingdom.|Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
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Zhou
Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, United Kingdom.
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Chen
Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, United Kingdom.
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Hesjedal