Twistronics

Our group has been at the forefront of theoretical studies of twisted materials, modeling the structural, electronic, and phononic properties that arise when two or more layered crystal lattices are twisted with respect to each other creating a moiré interference pattern with a length scale larger than the individual crystal lattices.

We were part of the first collaboration to detect unconventional superconductivity and also correlated insulating behavior in twisted graphene bilayers. By leveraging careful multiscale modeling techniqes, we were able to translate the energetics calculated using density functional theory (DFT) into accurate atomic relaxation patterns at the moiré scale, which are critical for the correct determination of the electronic band structure.

These modeling methods have been extended to the case of twisted graphene trilayers, as well as twisted systems built from transition metal dichalcogenides (TMDs). Changes in chemical composition, exemplified by the many combinations of Janus TMDs, combine with twist angles to yield a rich set of electronic properties. We have further studied the twist angle dependence of lattice vibrations in general bilayer systems, and are beginning to probe the effects of twisting on the electron-phonon coupling. Intercalation of small cations between the twisted bilayers is another area of recent interest.