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Zuowei Liang, Aiyun Luo, Mengzhu Shi, Qiang Zhang, Simin Nie, Jianjun Ying, Jun-Feng He, Tao Wu, Zhijun Wang, Gang Xu, Zhenyu Wang, Xianhui Chen
Abstract
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 $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ and $\mathrm{Mn}{\mathrm{Bi}}_{4}{\mathrm{Te}}_{7}$. We have determined the energy dispersion and helical spin texture of the surface states through quasiparticle interference patterns far above Dirac energy. Approaching the Dirac point, the native defects in the $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ 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.