Large magnetic gap at the Dirac point in a Mn-induced Bi${}_2$Te${}_3$ heterostructure

Abstract

Magnetically doped topological insulators enable the quantum anomalous Hall effect (QAHE) which provides quantized edge states for lossless charge transport applications. The edge states are hosted by a magnetic energy gap at the Dirac point but all attempts to observe it directly have been unsuccessful. The gap size is considered crucial to overcoming the present limitations of the QAHE, which so far occurs only at temperatures one to two orders of magnitude below its principle limit set by the ferromagnetic Curie temperature $T_C$. Here, we use low temperature photoelectron spectroscopy to unambiguously reveal the magnetic gap of Mn-doped Bi${}_2$Te${}_3$ films, which is present only below $T_C$. Surprisingly, the gap turns out to be $\sim$90 meV wide, which not only exceeds $k_{B}T$ at room temperature but is also 5 times larger than predicted by density functional theory. By an exhaustive multiscale structure characterization we show that this enhancement is due to a remarkable structure modification induced by Mn doping. Instead of a disordered impurity system, it forms an alternating sequence of septuple and quintuple layer blocks, where Mn is predominantly incorporated in the septuple layers. This self-organized heterostructure substantially enhances the wave-function overlap and the size of the magnetic gap at the Dirac point, as recently predicted. Mn-doped Bi${}_2$Se${}_3$ forms a similar heterostructure, however, only a large, nonmagnetic gap is formed. We explain both differences based on the higher spin-orbit interaction in Bi${}_2$Te${}_3$ with the most important consequence of a magnetic anisotropy perpendicular to the films, whereas for Bi${}_2$Se${}_3$ the spin-orbit interaction it is too weak to overcome the dipole-dipole interaction. Our findings provide crucial insights for pushing the lossless transport properties of topological insulators towards room-temperature applications.

arXiv comment23 pages, 5 figures

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• Variety of magnetic topological phases in the (MnBi${}_2$Te${}_4$)(Bi${}_2$Te${}_3$)${}_m$ family
• Observation of high-temperature quantum anomalous Hall regime in intrinsic MnBi${}_2$Te${}_4$/Bi${}_2$Te${}_3$ superlattice
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• Electric field induced topological phase transition and large enhancements of spin-orbit coupling and Curie temperature in two-dimensional ferromagnetic semiconductors
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• Analytical solution for the surface states of antiferromagnetic topological insulator MnBi${}_2$Te${}_4$
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• Tuning the magnetism and band topology through antisite defects in Sb doped MnBi4Te7
• Routes to realize the axion-insulator phase in MnBi${}_2$Te${}_4$(Bi${}_2$Te${}_3$)${}_n$ family: a perspective
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• Hybridization-Induced Gapped and Gapless States on the Surfaces of Magnetic Topological Insulators
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• Quantum Imaging of Magnetic Phase Transitions and Spin Fluctuations in Intrinsic Magnetic Topological Nanoflakes
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• Large Itinerant Electron Exchange Coupling in the Magnetic Topological Insulator MnBi2Te4
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• Robust high-temperature topological excitonic insulator of transition-metal carbides (MXenes)
• Approaching a Minimal Topological Electronic Structure in Antiferromagnetic Topological Insulator MnBi2Te4 via Surface Modification
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• Electrically Controlled Anomalous Hall Effect and Orbital Magnetization in Topological Magnet MnBi2Te4
• Metamagnetism of few layer topological antiferromagnets
• Gate-Tunable Quantum Anomalous Hall Effects in MnBi${}_2$Te${}_4$ Thin Films
• Antiferromagnetic VdW Phase at the Interface of Sputtered Topological Insulator/Ferromagnet-Bi2Te3/Ni80Fe20 Heterostructures
• Intrinsic magnetic topological insulators of the MnBi${}_2$Te${}_4$ family
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• Quantum Anomalous Hall Effect in Perfectly Compensated Collinear Antiferromagnetic Thin Films
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• Magnetization relaxation and search for the magnetic gap in bulk-insulating V-doped (Bi, Sb)${}_2$Te${}_3$
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