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Magnetically doped topological insulators enable the quantum anomalous Hall effect (QAHE), which provides quantized edge states for lossless charge-transport applications1–8. The edge states are hosted by a magnetic energy gap at the Dirac point2, 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 the QAHE, which so far occurs only at temperatures that are one to two orders of magnitude below the ferromagnetic Curie temperature, TC(ref. 8). Here we use low-temperature photoelectron spectroscopy to unambiguously reveal the magnetic gap of Mn-doped Bi2Te3, which displays ferromagnetic out-of-plane spin texture and opens up only below TC. Surprisingly, our analysis reveals large gap sizes at 1 kelvin of up to 90 millielectronvolts, which is five times larger than theoretically predicted9. Using multiscale analysis we show that this enhancement is due to a remarkable structure modification induced by Mn doping: instead of a disordered impurity system, a self-organized alternating sequence of MnBi2Te4septuple and Bi2Te3quintuple layers is formed. This enhances the wavefunction overlap and size of the magnetic gap10. Mn-doped Bi2Se3(ref. 11) and Mn-doped Sb2Te3form similar heterostructures, but for Bi2Se3only a nonmagnetic gap is formed and the magnetization is in the surface plane. This is explained by the smaller spin–orbit interaction by comparison with Mn-doped Bi2Te3. Our findings provide insights that will be crucial in pushing lossless transport in topological insulators towards room-temperature applications.

High energy resolution fast XPS combined with TPD experiments were used to study the effect of chemisorbed oxygen on the adsorption and dissociation of NH3on Ir110. Below 250 K the presence of Oaddoes not influence NH3decomposition. Above 250 K Oadenhances NH3dissociation, which results in three times as much N2formation and less molecular NH3desorption compared to the experiments without Oad. The effect of Oadcan be attributed to destabilization of NHadon the surface, resulting in a further dehydrogenation towards Nad. The presence of Oadon the surface lowers the temperature at which the Nadcombination reaction takes place by as much as 200 K, due to repulsive interaction between Nadand Oad. NO is formed above 450 K if both Nadand Oadare present on the surface.