Comparative studies of MBE-grown MnBi₂Te₄ on Si(111) and epitaxial graphene substrates

Discerning the topological surface state is critical for understanding exotic quantum phenomena including the Quantum Anomalous Hall effect and Axion insulator states in intrinsic magnetic topological insulators (MTI). In order to achieve an intrinsic surface state of MnBi₂Te₄, the sample thickness must be controlled down to a very thin regime where the complexity added by underlying anti-site defects is minimized. Using molecular beam epitaxy (MBE), we gain control of high-quality MnBi₂Te₄ and MnBi₂Te₄/Bi₂Te₃ super-lattice growths to exploit their rich topological quantum phase diagram. By combining in-situ electron diffraction and ex-situ x-ray diffraction techniques we report differences in the preferred alignment of MnBi₂Te₄ depending on sample interactions with different substrates (e.g. Si(111), epitaxial graphene) during the growth. We further investigate characteristic electronic structures at the surface of weakly bonded MnBi₂Te₄ flakes formed on top of van der Waals substrates (Gr/SiC, HOPG) compared to Si(111), using in-situ STM and ARPES.