Native point defects and their implications for the Dirac point gap at MnBi₂Te₄(0001)

2021/09/03 by M. Garnica, M. M. Otrokov, Garnica, M. +34 · 6 citations
Materials Science · Physics and Astronomy · #Angle-resolved photoemission spectroscopy #Antiferromagnetism #Band gap #Condensed matter physics #Density functional theory #Electronic structure #FOS: Physical sciences #Geometry #Iron-based superconductors research #Materials Science (cond-mat.mtrl-sci) #Materials science #Nuclear magnetic resonance #Photoemission spectroscopy #Physics #Physics of Superconductivity and Magnetism #Quantum mechanics #Scanning tunneling microscope #Semimetal #Surface (topology) #Surface states #Topological Materials and Phenomena #Topological insulator #X-ray photoelectron spectroscopy #cond-mat.mtrl-sci

paper · pdf · doi:10.48550/arxiv.2109.01615

published in arXiv (Cornell University) (Cornell University)

arxiv created 2021/09/03 · openalex publication_date 2021/09/03 · arxiv updated 2021/09/06 · openalex created_date 2022/12/25 · openalex updated_date 2026/08/09

Abstract

The Dirac point gap at the surface of the antiferromagnetic topological insulator MnBi₂Te₄ is a highly debated issue. While the early photoemission measurements reported on large gaps in agreement with theoretical predictions, other experiments found vanishingly small splitting of the MnBi₂Te₄ Dirac cone. Here, we study the crystalline and electronic structure of MnBi₂Te₄(0001) using scanning tunneling microscopy/spectroscopy (STM/S), micro(μ)-laser angle resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations. Our topographic STM images clearly reveal features corresponding to point defects in the surface Te and subsurface Bi layers that we identify with the aid of STM simulations as Bi_Te antisites (Bi atoms at the Te sites) and Mn_Bi substitutions (Mn atoms at the Bi sites), respectively. X-ray diffraction (XRD) experiments further evidence the presence of cation (Mn-Bi) intermixing. Altogether, this affects the distribution of the Mn atoms, which, inevitably, leads to a deviation of the MnBi₂Te₄ magnetic structure from that predicted for the ideal crystal structure. Our transport measurements suggest that the degree of this deviation varies from sample to sample. Consistently, the ARPES/STS experiments reveal that the Dirac point gap of the topological surface state is different for different samples/sample cleavages. Our DFT surface electronic structure calculations show that, due to the predominant localization of the topological surface state near the Bi layers, Mn_Bi defects can cause a strong reduction of the MnBi₂Te₄ Dirac point gap, given the recently proved antiparallel alignment of the Mn_Bi moments with respect to those of the Mn layer. Our results provide a key to puzzle out the MnBi₂Te₄ Dirac point gap mystery.

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