Massive Dirac fermion observed in lanthanide-doped topological insulator thin films
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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.
Harrison , S E , Collins-McIntyre , L J , Schönherr , P , Vailionis , A , Srot , V , Van Aken , P A , Kellock , A J , Pushp , A , Parkin , S S P , Harris , J S , Zhou , B , Chen , Y L & Hesjedal , T 2015 , ' Massive Dirac fermion observed in lanthanide-doped topological insulator thin films ' Scientific Reports , vol 5 , 15767 . DOI: 10.1038/srep15767
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This publication arises from research funded by the John Fell Oxford University Press (OUP) Research Fund, a DARPA MESO Project (No. N66001-11-1-4105), and funding from the European Union Seventh Framework Programme under Grant Agreement 312483 – ESTEEM2 (Integrated Infrastructure Initiative I3) and transnational access to MPI-IS (WP13). Part of this work was performed at the Stanford Nano Shared Facilities (SNSF). S.E.H. was supported by the VPGE (Stanford University), L.C.M. by EPSRC (UK), and P.S. acknowledges partial funding from EPSRC, Corpus Christi College (Oxford), and the Studienstiftung des deutschen Volkes (Germany).