Scanning Tunneling Microscopy Study of Epitaxially Grown Fe₃GeTe₂ Layer on the Topological Insulator Bi₂Te₃

Introducing magnetism to the surface state of topological insulators, such as Bi₂Te₃, can lead to a variety of interesting phenomena such as magnetoelectric effects, Weyl semimetal phases, and the quantum anomalous Hall effect. We use spin-polarized scanning tunneling microscopy to study a single quintuple layer (QL) of Fe₃GeTe₂ (FGT) that is grown on Bi₂Te₃ via molecular beam epitaxy. FGT is a 2D ferromagnetic van der Waals material with a Curie temperature (Tc) that can exceed room temperature. Large topographic images show that the FGT grows as isolated islands on Bi₂Te₃ and from Bi₂Te₃ steps. Atomic resolution imaging shows atomic lattices of 3.9(9)Å for FGT and 4.4(0)Å for Bi₂Te₃. The FGT has a Moire pattern with a periodicity of 4.38(6)nm attributed solely to the lattice mismatch showing that the FGT is rotationally aligned to the Bi₂Te₃. Much of the surface is covered by a single QL of the FGT, with some small double QL regions. There are also regions with partial terminations, where the second quintuple layer is incomplete. The most common partial termination is the FeGe layer, in which the top two atomic layers are missing. This termination has a distinctive electronic structure and a root 3 reconstruction resulting in a 6.8Å lattice constant on top of the Moire pattern associated with the FGT 3.9(9)Å atomic lattice. Preliminary measurements have been done in a magnetic field with an anti-ferromagnetic Cr tip to probe the magnetic structure and search for magnetic textures.