Exploring correlated and topological quantum phases in twisted bilayer crystals
Sanfeng Wu, Assistant Professor of Physics
Seed start and end dates: November 1, 2018 - October 31, 2019
One of the remarkable contributions of graphene research over the past decade is to teach us how to realize high quality 2D electronic systems in the simplest settings – materials with only a single atomic layer. In such atomic monolayers, the quantum electronic properties can be unprecedently controlled through external fields or van der Waals interface engineering. For instance, stacking two monolayer crystals in a twisted fashion can result in long wavelength Moiré patterns (Fig. 1A-C), which can significantly alter the electronic bands at low energies. At certain “magic” twist angles, the band can even be tuned to be very flat. In the case of graphene, this “twistronics” approach creates a flat band at an angle near 1.1o, leading to the observation of superconductivity. In general, it has pointed to a new, fascinating route to achieve flat bands and strong electron correlations without introducing any disorder, through controlling the stacking parameters of a van der Waals heterostructure.
An electronic flat band not only holds the promise to achieve high-Tc superconductivity, but also could lead to the observation of fractionalized quantum states at zero magnetic field. The latter requires the development of a flat band with strong spin-orbit coupling and non-trivial topology. However, graphene itself has very weak spin-orbit coupling, and its electronic band is topologically trivial at finite temperatures. Hence, it is of great interest to apply the twistronics approach to other 2D crystals, especially those with non-trivial topology.