Crossover from 2D ferromagnetic insulator to wide bandgap quantum anomalous Hall insulator in ultra-thin MnBi2Te4

Abstract

Intrinsic magnetic topological insulators offer low disorder and large magnetic bandgaps for robust magnetic topological phases operating at higher temperatures. By controlling the layer thickness, emergent phenomena such as the Quantum Anomalous Hall (QAH) effect and axion insulator phases have been realised. These observations occur at temperatures significantly lower than the Neel temperature of bulk MnBi2Te4, and measurement of the magnetic energy gap at the Dirac point in ultra-thin MnBi2Te4 has yet to be achieved. Critical to achieving the promise of this system is a direct measurement of the layer-dependent energy gap and verifying whether the gap is magnetic in the QAH phase. Here we utilise temperature dependent angle-resolved photoemission spectroscopy to study epitaxial ultra-thin MnBi2Te4. We directly observe a layer dependent crossover from a 2D ferromagnetic insulator with a bandgap greater than 780 meV in one septuple layer (1 SL) to a QAH insulator with a large energy gap (>100 meV) at 8 K in 3 and 5 SL MnBi2Te4. The QAH gap is confirmed to be magnetic in origin, as it abruptly diminishes with increasing temperature above 8 K. The direct observation of a large magnetic energy gap in the QAH phase of few-SL MnBi2Te4 is promising for further increasing the operating temperature of QAH materials.

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Cited by in corpus (16)

• Colloquium: Quantum anomalous Hall effect
• Even-Odd Layer-Dependent Anomalous Hall Effect in Topological Magnet MnBi2Te4 Thin Films
• Local manifestations of thickness dependent topology and axion edge state in topological magnet MnBi${}_2$Te${}_4$
• An antiferromagnetic diode effect in even-layered MnBi2Te4
• Intrinsic magnetic topological insulators of the MnBi${}_2$Te${}_4$ family
• Evolution of the electronic structure of ultrathin MnBi2Te4 Films
• Coexistence of Superconductivity and Antiferromagnetism in Topological Magnet MnBi2Te4 Films
• Roadmap on Quantum Magnetic Materials
• Formation of a stable surface oxide in MnBi${}_2$Te${}_4$ thin films
• Imaging the breakdown and restoration of topological protection in magnetic topological insulator MnBi${}_2$Te${}_4$
• Correlation between magnetic domain structures and quantum anomalous Hall effect in epitaxial MnBi2Te4 thin films
• Magnetization relaxation and search for the magnetic gap in bulk-insulating V-doped (Bi, Sb)${}_2$Te${}_3$
• Reversing Neel Vector in PT-Antiferromagnets by Nonreciprocal Light Scattering
• Topological fluctuating electron-hole Cooper pairs in graphene-GaAs heterostructures
• Strain effect on optical properties and quantum weight of monolayer MnBi${}_2$X${}_4$ (X = Te, Se, S)
• Topological hybrid electron-hole Cooper pairing