Probing the magnetic band gap of the ferromagnetic topological insulator MnSb2Te4
Abstract
Mn-rich MnSb2Te4 is a ferromagnetic topological insulator with yet the highest Curie temperature TC = 45-50 K. It exhibits a magnetic gap at the Dirac point of the topological surface state that disappears above TC. By scanning tunneling spectroscopy, we probe this gap at different magnetic fields and temperatures. We firstly reveal that the gap size shrinks, when an in-plane magnetic field of up to B = 3 T is applied, but does not close completely as the magnetization is only partially rotated in-plane. This corroborates the magnetic origin of the gap and the complex magnetic structure. In addition, we demonstrate significant spatiotemporal fluctuations of the gap size at temperatures as low as TC/2, above which the remanent magnetization indeed decays. This temperature is close to the antiferromagnetic transition temperature observed for bulk-type single crystals of MnSb2Te4, highlighting the important role of competing magnetic orders in the formation of the favorable ferromagnetic topological insulator. Our study, thus, provides crucial insights into the complex magnetic gap opening of topological insulators that is decisive for quantum anomalous Hall devices.
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