Supercell Formation in Epitaxial Rare-Earth Ditelluride Thin Films

Square-net tellurides host an array of electronic ground states and commonly exhibit charge-density-wave ordering. Here, we report the epitaxy of DyTe2-delta on atomically flat MgO (001) using molecular beam epitaxy. The films are single phase and highly oriented, as evidenced by transmission electron microscopy and X-ray diffraction measurements. Epitaxial strain is evident in films and is relieved as the thickness increases up to a value of approximately 20 quintuple layers. Diffraction features associated with a supercell in the films are resolved, which is coupled with Te-deficiency. First principles calculations attribute the formation of this defect lattice to nesting conditions in the Fermi surface, which produce a periodic occupancy of the conducting Te square-net and open a band gap at the chemical potential. This work establishes the groundwork for exploring the role of strain in tuning the electronic and structural phases of epitaxial square-net tellurides and related compounds.