Scattering of phonons in hexagonal 2D crystals on their domain boundaries

The scattering of phonons in two-dimensional hexagonal crystals at their defect boundaries are investigated. These so-called Wigner crystals exist in different monolayer and bilayer forms and present a rich variety of defect boundaries. To fix the calculation we investigate phonon scattering for the physisorbed monolayers on solid surfaces, that exhibit two types of domain boundaries called heavy and superheavy solitons delimiting the crystalline ordered phase domains. A detailed study is presented for the reflection and transmission of the two-dimensional 2D crystal phonons at these domain boundaries, where the scattering spectra are related to the change of their elastic constants. Fano resonances may appear in the phonon transmission spectra due to the coherent coupling between the 2D crystal phonons and the localised vibration modes on the domain boundary. For a resonator cavity made up of two such domain boundaries, additional Fabry-Perot oscillations are found in the scattering spectra.