Kin Fai Mak from Cornell University gave a presentation on the “Correlated Excitonic States In A Moiré Lattice” that focused on the trapping of exciton using Moiré lattices. An exciton is formed when an electron in a crystal lattice orbits an electron hole (or just “hole” for simplicity). As the electron orbits the hole, it generates a mobile coulombic force that also emits an electric field. If a lattice is composed of 2D sheets or films, then a Moiré lattice can be formed by shifting one of the sheets so as to generate a new recurrent structure.
In order to form a Moiré lattice, the research team began by joining 2 layers of a semiconducting materials. But to contain excitons in that lattice, one layer had an excess of electrons (N-type layer) and the other had an excess of holes (P-type layer). Then, they confirmed the presence of excitons in their Moiré lattice by measuring the differential capacitance in the system which was altered due to the exciton’s emitted electric field. This simplistic setup favors the trapping of excitons by the formation of electron-hole pairs, while simultaneously eliminating any significant electron-hole wavefunction overlap.
If you are interested in the study of excitonic solids or other new materials and their strong correlations click here to watch the full symposium session.