Topological electronic crystals in twisted bilayer-trilayer graphene

TL;DR

This paper reports the observation of topological electronic crystals in twisted bilayer-trilayer graphene, driven by moire potential, exhibiting tunable quantum anomalous Hall effects and multiple topological states at various fillings.

Contribution

It demonstrates the realization of a generalized anomalous Hall crystal in twisted bilayer-trilayer graphene with tunable Chern numbers and multiple topological phases induced by moire patterns.

Findings

Observation of a topological electron crystal at ν=1/4 with quantum anomalous Hall effect.

Reversible switching of Chern number between +1 and -1 via electric and magnetic fields.

Emergence of various topological crystals at different magnetic field and filling factors.

Abstract

In a dilute two-dimensional electron gas, Coulomb interactions can stabilize the formation of a Wigner crystal. Although Wigner crystals are topologically trivial, it has been predicted that electrons in a partially-filled band can break continuous translational symmetry and time-reversal symmetry spontaneously to form a form of topological electron crystal known as an anomalous Hall crystal. Here, we report the observation of a generalized version of the anomalous Hall crystal in twisted bilayer-trilayer graphene, whose formation is driven by the moire potential. The crystal forms at a band filling factor of one electron per four moir\'e unit cells ($\nu=1/4$) and quadruples the unit-cell area, coinciding with an integer quantum anomalous Hall effect. The Chern number of the state is exceptionally tunable, and can be switched reversibly between $+1$ and $-1$ by electric and magnetic fields. Several other topological electronic crystals arise in a modest magnetic field, originating from $\nu=1/3$, $1/2$, $2/3$, and $3/2$. The quantum geometry of the folded bands is likely very different from that of the original parent band, enabling possible future discoveries of correlation-driven topological phenomena