Nature of the Dirac gap modulation and surface magnetic interaction in axion antiferromagnetic topological insulator MnBi${}_2$Te${}_4$

Abstract

Modification of the gap at the Dirac point (DP) in antiferromagnetic (AFM) axion topological insulator MnBi${}_2$Te${}_4$ and its electronic and spin structure has been studied by angle- and spin-resolved photoemission spectroscopy (ARPES) under laser excitation with variation of temperature (9-35~K), light polarization and photon energy. We have distinguished both a large (62-67~meV) and a reduced (15-18~meV) gap at the DP in the ARPES dispersions, which remains open above the Néel temperature ($T_{\mathrm{N}}=24.5$~K). We propose that the gap above $T_{\mathrm{N}}$ remains open due to short-range magnetic field generated by chiral spin fluctuations. Spin-resolved ARPES, XMCD and circular dichroism ARPES measurements show a surface ferromagnetic ordering for large-gap sample and significantly reduced effective magnetic moment for the reduced-gap sample. These effects can be associated with a shift of the topological DC state towards the second Mn layer due to structural defects and mechanical disturbance, where it is influenced by a compensated effect of opposite magnetic moments.

References in corpus (8)

• Topological Field Theory of Time-Reversal Invariant Insulators
• Quantized Anomalous Hall Effect in Magnetic Topological Insulators
• Skyrmion fractionalization and merons in chiral magnets with easy-plane anisotropy
• Dimensional Crossover Induced Topological Hall Effect in a Magnetic Topological Insulator
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• Josephson currents induced by the Witten effect
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Cited by in corpus (3)

• Spin-polarized imaging of the antiferromagnetic structure and field-tunable bound states in kagome magnet FeSn
• Antiferromagnetic topological insulator with selectively gapped Dirac cones
• Intermediate anomalous Hall states induced by noncollinear spin structure in magnetic topological insulator MnBi2Te4