Sample-dependent Dirac point gap in MnBi${}_2$Te${}_4$ and its response to the applied surface charge: a combined photoemission and ab initio study

Abstract

Recently discovered intrinsic antiferromagnetic topological insulator MnBi${}_2$Te${}_4$ presents an exciting platform for realization of the quantum anomalous Hall effect and a number of related phenomena at elevated temperatures. An important characteristic making this material attractive for applications is its predicted large magnetic gap at the Dirac point (DP). However, while the early experimental measurements reported on large DP gaps, a number of recent studies claimed to observe a gapless dispersion of the MnBi${}_2$Te${}_4$ Dirac cone. Here, using micro($\mu$)-laser angle-resolved photoemission spectroscopy, we study the electronic structure of 15 different MnBi${}_2$Te${}_4$ samples, grown by two different chemists groups. Based on the careful energy distribution curves analysis, the DP gaps between 15 and 65 meV are observed, as measured below the Néel temperature at about 10-16 K. At that, roughly half of the studied samples show the DP gap of about 30 meV, while for a quarter of the samples the gaps are in the 50 to 60 meV range. Summarizing the results of both our and other groups, in the currently available MnBi${}_2$Te${}_4$ samples the DP gap can acquire an arbitrary value between a few and several tens of meV. Further, based on the density functional theory, we discuss a possible factor that might contribute to the reduction of the DP gap size, which is the excess surface charge that can appear due to various defects in surface region. We demonstrate that the DP gap is influenced by the applied surface charge and even can be closed, which can be taken advantage of to tune the MnBi${}_2$Te${}_4$ DP gap size.

References in corpus (6)

• Topological Field Theory of Time-Reversal Invariant Insulators
• Crystal growth and magnetic structure of MnBi2Te4
• Emergent quantum confinement at topological insulator surfaces
• Robust A-type order and spin-flop transition on the surface of the antiferromagnetic topological insulator MnBi${}_2$Te${}_4$
• Coexistence of Surface Ferromagnetism and Gapless Topological State in MnBi${}_2$Te${}_4$
• Trigger of the ubiquitous surface band bending in 3D topological insulators

Cited by in corpus (2)

• Symmetry analysis of magnetoelectric effects in perovskite-based multiferroics
• Facet dependent surface energy gap on magnetic topological insulators