Magnetically doped topological insulators enable the quantum anomalous Hall effect(QAHE), which provides quantized edge states for lossless charge-transportapplications1–8. The edge states are hosted by a magnetic energy gap at the Diracpoint2, but hitherto all attempts to observe this gap directly have been unsuccessful.Observing the gap is considered to be essential to overcoming the limitations of theQAHE, which so far occurs only at temperatures that are one to two orders ofmagnitude below the ferromagnetic Curie temperature, TC (ref. 8). Here we use lowtemperaturephotoelectron spectroscopy to unambiguously reveal the magnetic gapof Mn-doped Bi2Te3, which displays ferromagnetic out-of-plane spin texture andopens up only below TC. Surprisingly, our analysis reveals large gap sizes at 1 kelvin ofup to 90 millielectronvolts, which is five times larger than theoretically predicted9.Using multiscale analysis we show that this enhancement is due to a remarkablestructure modification induced by Mn doping: instead of a disordered impuritysystem, a self-organized alternating sequence of MnBi2Te4 septuple and Bi2Te3quintuple layers is formed. This enhances the wavefunction overlap and size of themagnetic gap10. Mn-doped Bi2Se3 (ref. 11) and Mn-doped Sb2Te3 form similarheterostructures, but for Bi2Se3 only a nonmagnetic gap is formed and themagnetization is in the surface plane. This is explained by the smaller spin–orbitinteraction by comparison with Mn-doped Bi2Te3. Our findings provide insights thatwill be crucial in pushing lossless transport in topological insulators towards roomtemperatureapplications.
- Advanced Materials Science
- Basic - Fundamental (Grundlagenforschung)