Abstract
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.
Highlights
The breaking of time reversal symmetry (TRS) in three-dimensional (3D) topological insulators (TIs), and the opening of a ‘Dirac-mass gap’ in the linearly dispersed Dirac surface state, is a prerequisite for unlocking exotic physical states
Doping of the prototypical 3D-TIs1,2 (Bi,Sb)2(Se,Te)[3] with transition metal ions can lead to ferromagnetic ordering at low temperatures[3,4]
The lanthanide (Ln) 4f series comprises the elements from La to Yb, which are most commonly found in a + 3 oxidation state, allowing for an isoelectronic substitution of Bi
Summary
Energy distribution curves (EDC) at k =0 were obtained to investigate the reduced spectral intensity and to explore the possibility of a magnetic doping induced gap, which are shown on the right-hand side of Fig. 4a–d. It has been suggested that impurity scattering may play a more significant role than previously considered[21,22] This paradox is highlighted further by comparing theoretical and experimental studies on Mn-doped Bi2Te3 and Bi2Se3 systems which have experimentally detected gaps up to an order of magnitude larger than theoretically predicted values and persist well above the Curie temperatures[18,23]. In light of these theoretical challenges, only exploratory materials science can tell whether a Ln doped system behaves as expected, or holds unforeseen surprises
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