Inducing magnetism into topological insulators is intriguing for utilizing exotic phenomena such as the quantum anomalous Hall effect (QAHE) for technological applications. While most studies have focused on doping magnetic impurities to open a gap at the surface-state Dirac point, many undesirable effects have been reported to appear in some cases that makes it difficult to determine whether the gap opening is due to the time-reversal symmetry breaking or not. Furthermore, the realization of the QAHE has been limited to low temperatures. Here we have succeeded in generating a massive Dirac cone in a MnBi2Se4/Bi2Se3 heterostructure, which was fabricated by self-assembling a MnBi2Se4 layer on top of the Bi2Se3 surface as a result of the codeposition of Mn and Se. Our experimental results, supported by relativistic ab initio calculations, demonstrate that the fabricated MnBi2Se4/Bi2Se3 heterostructure shows ferromagnetism up to room temperature and a clear Dirac cone gap opening of ∼100 meV without any other significant changes in the rest of the band structure. It can be considered as a result of the direct interaction of the surface Dirac cone and the magnetic layer rather than a magnetic proximity effect. This spontaneously formed self-assembled heterostructure with a massive Dirac spectrum, characterized by a nontrivial Chern number C = −1, has a potential to realize the QAHE at significantly higher temperatures than reported up to now and can serve as a platform for developing future “topotronics” devices.

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Superconducting radiofrequency (SRF) cavities for accelerators is the only superconductivity application that operates in the Meissner state. For decades, bulk niobium, which exhibits the highest 1st critical field among all known superconductors, has been the only material to achieve high accelerating fields in combination with a high quality factor. Specific nanostructures tailored for SRF applications, in the form of superconducting/insulating/superconducting multilayers, were proposed to surpass Nb performances that could improve SRF performance. In this paper, we present the study of a series of NbN/MgO/Nb tri-layers including standard material characterization and specific superconducting characterization (local magnetometry) along with a comparison to the current state-of-the-art theoretical modeling. This study shows that such structures are effective to enhance the penetration field compared to bare niobium, even in the presence of numerous defects.