When a magnetic field is applied perpendicular to the current flow in a conductor, a transverse voltage appears due to the well-known Hall effect. If the conductor has ferromagnetic ordering, then this voltage can emerge without the need for an external magnetic field. The quantum version of this anomalous Hall effect is topological in nature; unlike its ordinary counterpart whose origins date back to the nineteenth century, the quantum anomalous Hall effect is extremely difficult to realize experimentally. Christian Crisostomo and colleagues have now predicted that chemical functionalization could provide new platforms for developing robust quantum anomalous Hall phases.
By magnetically doping topological insulator thin films, quantum anomalous Hall states have already been realized, but only at very low temperatures. Using first-principles calculations, Crisostomo et al. showed that chemical functionalizing with hydrogen or nitrogen atoms could enable certain bismuth-based materials with a honeycomb lattice to host quantum anomalous Hall phases with bandgaps that are much larger than current realizations, making them more stable. As such phases support chiral edge states that are fully spin-polarized, this could provide new opportunities for spintronics and low-power electronic devices.
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Fleet, L. Honeycomb recipe. Nature Phys 13, 1037 (2017). https://doi.org/10.1038/nphys4319