We study the surface crystalline and electronic structures of the antiferromagnetic topological insulator MnBi2Te4 using scanning tunneling microscopy/spectroscopy (STM/S), micro(μ)-laser angle-resolved photoemission spectroscopy (ARPES), and density functional theory calculations. Our STM images reveal native point defects at the surface that we identify as BiTe antisites and MnBi substitutions. Bulk X-ray diffraction further evidences the presence of the Mn-Bi intermixing. Overall, our characterizations suggest that the defects concentration is nonuniform within crystals and differs from sample to sample. Consistently, the ARPES and STS experiments reveal that the Dirac point gap of the topological surface state is different for different samples and sample cleavages, respectively. Our calculations show that the antiparallel alignment of the MnBi moments with respect to those of the Mn layer can indeed cause a strong reduction of the Dirac point gap size. The present study provides important insights into a highly debated issue of the MnBi2Te4 Dirac point gap.

Note that the quantities in rows 1-3 and the exchange coupling parameters in rows 4 and 5 are calculated with two very different methods and codes. See Methods section for details. ** Calculated/experimental values.

bly because of the obvious difficulties in the preparation of MnBi 2 Te 4 • n(Bi 2 Te 3 ) with high index n and unavailability of samples.We have succeeded in this regard and present here the crystal structure of the members with n = 4, 5, and 6, summarize all available structural data for MnBi 2 Te 4 • n(Bi 2 Te 3 ), trace the evolution of Raman spectra of MnBi 2 Te 4 • n(Bi 2 Te 3 ) that embraces all n from 0 to 6 as well as n = ∞ (Bi 2 Te 3 ), and provide a thorough analysis of the obtained Raman data. II. SYNTHESIS AND CRYSTAL STRUCTUREOF MnBi 2 Te 4 • n(Bi 2 Te 3 )A. Synthesis and crystal growth