Deep Quantum-Dot Arrays in Moiré Superlattices of Non-van der Waals Materials.

Abstract

Recently, moiré superlattices of twisted van der Waals (vdW) materials have attracted substantial interest due to their strongly correlated properties. However, the vdW interlayer interaction is intrinsically weak, such that many desired properties can only exist at low temperature. Here, we theoretically predict some unusual properties stemming from the chemical bonding between twisted PbS nanosheets as an example of non-vdW moiré superlattices. The strong interlayer coupling in such systems results in giant strain vortices and dipole vortices at the interface. The modified electronic structures become a series of dispersionless bands and artificial-atom states. In real space, these states are analogous to arrays of well-positioned quantum dots, which may be promising for use in single-electron devices. In theory, if the materials are doped with a low concentration of electrons, a Wigner crystal will form even without any magnetic field. To confirm the accessibility and stability of non-vdW moiré superlattices in experiment, we synthesized PbS moiré superlattices with different twist angles. Our transmission-electron-microscope observations reveal the resemblance of the small-angle-twisted structures with the square matrices of quantum dots, which is in good accordance with our calculations.