Van der Waals epitaxy between the highly lattice mismatched Cu-doped FeSe and Bi2Te3

We present a structural and density functional theory study of FexCu1-xSe within the three-dimensional topological insulator Bi2Te3. The FexCu1-xSe inclusions are single-crystalline and epitaxially oriented with respect to the Bi2Te3 thin film. Aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy show an atomically sharp FeICu1-xSe/Bi2Te3 interface. The FexCu1-xSe/Bi2Te3 interface is determined by Se-Te bonds and no misfit dislocations are observed, despite the different lattice symmetries and large lattice mismatch of [sim]19%. First-principle calculations show that the large strain at the FexCu1-xSe/Bi2Te3 interface can be accommodated by van der Waals-like bonding between Se and Te atoms.