Correlated Topological Electronic States and Surface Magnetic Orderings in Layered MnBi₂Te₄

Magnetic van der Waals (vdW) layered materials has inspired enormous interest recently by utilizing the spin degree of freedom for applications in next-generation 2D spintronic devices. Among these materials, MnBi₂Te₄ provides topological bands and the alternating ferromagnetic / antiferromagnetic ordering simultaneously, thus serves as an ideal system promising for 2D spintronics. However, many controversies and discrepancies between theoretical predictions and experimental observations remain unclarified, mainly due to unclarified correlations between electronic bands and surface magnetic ordering. Here, we performed intensive studies of low temperature scanning tunneling microscopy/spectroscopy (STM/S) on high-quality single crystal of MnBi₂Te₄, rationalized with density functional theory (DFT) calculations. Topological surface states (TSSs) and the dispersions are clearly observed by quasiparticle interference (QPI) imaging. The asymmetric QPI patterns at the energies near Dirac point, strongly suggest that the magnetization of the Mn layer in the topmost septuple-layer can be canted into the in-plane direction, which is responsible for the observations of gapless TSSs. Furthermore, various bulk bandgaps observed at the temperatures below and above the Nèel temperature or at the edge of surface terraces, implies a variety of band structures correlated with rich magnetic orders in the surface Mn layer. Our results provide an in-depth understanding of correlations between topological electronic structures and magnetic ordering of surface layer in magnetic topological insulator MnBi₂Te₄, as well as spin-dependent transport properties in spintronic devices.