Condensed Matter Theory Forum - Symmetry-broken states in twisted graphene multilayers

A wide family of novel moiré quantum materials can be assembled simply by stacking and twisting sheets of graphene. The physics of these materials depends sensitively on the overall number of graphene layers in the structure, as well as the stacking configuration and relative rotation angle between each. Here, I will discuss an array of symmetry-broken states that emerge in twisted M+N graphene multilayers, defined as structures created by slightly rotating an M-layer graphene sheet atop an N-layer graphene sheet. In particular, I will focus on twisted monolayer-bilayer graphene (1+2) and twisted double bilayer graphene (2+2), in which we observe a variety of strongly correlated states that can be tuned with external control knobs such as charge doping, electric field, pressure, and more. In addition to fully spin- and valley-polarized states, we see signatures of more exotic symmetry-breaking including charge density waves and inter-valley coherent states. We additionally observe topological states including an incipient quantum anomalous Hall effect and correlated Chern insulators, which depend sensitively on the twist angle and stacking chirality of the structures. Overall, our results demonstrate the extraordinary tunability of correlated and topological states in twisted graphene multilayers.