Mapping Dirac fermions in the intrinsic antiferromagnetic topological insulators (MnBi_2Te_4)(Bi_2Te_3)_n (n = 0, 1)

摘要

Nontrivial band topology combined with magnetic order can lead to rich emergent phenomena, including quantized anomalous Hall effect and axion insulator state. Here we use scanning tunneling microscopy to image the surface Dirac fermions of the newly discovered magnetic topological insulators MnBi_2Te_4 and MnBi_4Te_7. We have determined the energy dispersion and helical spin texture of the surface slates through quasiparticle interference patterns far above Dirac energy. Approaching the Dirac point, the native defects in the MnBi_2Te_4 septuple layer give rise to resonance states which extend spatially and potentially hinder the detection of a mass gap in the spectra. Our results impose tight constraints on the magnitude of the possible mass gap at the nanoscale and provide key ingredients for a comprehensive understanding of the electronic structure in this class of fascinating materials.