Quantum effects are most noticeable at extremely low temperatures, which limits their usefulness for technical applications. Thin films of MnSb_{2}Te_{4}, however, show new talents due to a small excess of manganese. Apparently, the resulting disorder provides spectacular properties: The material proves to be a topological insulator and is ferromagnetic up to comparatively high temperatures of 50 Kelvin, measurements at BESSY II show. This makes this class of material suitable for quantum bits, but also for spintronics in general or applications in high-precision metrology.

Quantum effects such as the anomalous quantum Hall effect enable sensors of highest sensitivity, are the basis for spintronic components in future information technologies and also for qubits in quantum computers of the future. However, as a rule, the quantum effects relevant for this only show up clearly enough to make use of them at very low temperatures near absolute zero and in special material systems.

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**Image: **The Dirac cone is typical for topological insulators and is practically unchanged on all 6 images (ARPES measurements at BESSY II). The blue arrow additionally shows the valence electrons in the volume. The synchrotron light probes both and can thus distinguish the Dirac cone at the surface (electrically conducting) from the three-dimensional volume (insulating).

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