Moiré modulation of lattice strains in PdTe2 quantum Films

Abstract

We report the epitaxial growth of PdTe2 ultrathin films on a topological insulator Bi2Se3. A prominent moiré pattern was observed in scanning tunneling microscope measurements. The moiré periodicity increases as film thickness decreases, indicating a lattice expansion of epitaxial PdTe2 thin films at lower thicknesses. In addition, our simulations based on a multilayer relaxation technique reveal uniaxial lattice strains at the edge of PdTe2 domains, and anisotropic strain distributions throughout the moiré supercell with a net change in lattice strain up to ∼2.9%. Our density functional theory calculations show that this strain effect leads to a narrowing of the band gap at Γ point near the Fermi level. Under a strain of ∼2.8%, the band gap at Γ closes completely. Further increasing the lattice strain makes the band gap reopen and the order of conduction band and valence bands inverted in energy. The experimental and theoretical results shed light on a method for constructing quantum grids of topological band structure under the modulation of moiré potentials.