Continuously tunable anomalous Hall crystals in rhombohedral heptalayer graphene

TL;DR

This paper reports the experimental discovery of tunable anomalous Hall crystals with high Chern numbers in rhombohedral heptalayer graphene moiré superlattices, revealing complex topological and correlated electronic states.

Contribution

It provides the first experimental observation of incommensurate anomalous Hall crystals with tunable Chern numbers in rhombohedral graphene moiré systems.

Findings

Observation of incommensurate Chern insulators with C=1 near v=1.

Detection of spontaneous time-reversal symmetry breaking and anomalous Hall effects.

High Chern number C=3 anomalous Hall crystals over a range of fillings.

Abstract

The interplay of electronic interactions and nontrivial topology can give rise to a wealth of exotic quantum states. A notable example is the formation of Wigner crystals driven by strong electron-electron interactions. When these electronic crystals emerge in a parent band carrying a large Berry curvature, they can exhibit topologically nontrivial properties as anomalous Hall crystals, spontaneously breaking both continuous translational symmetry and time-reversal symmetry. Here, we report the experimental observation of tunable anomalous Hall crystals in rhombohedral heptalayer graphene moir\'e superlattices. At filling factors near one electron per moir\'e unit cell (v=1), we identify a series of incommensurate Chern insulators with a Chern number of C=1. Furthermore, we observe spontaneous time-reversal symmetry breaking spanning the entire filling range from v=1 to v=2, manifesting as anomalous Hall effects with pronounced magnetic hysteresis. Notably, anomalous Hall crystals with a high Chern number C=3 are observed over generic fillings ranging from v=1.5 to v=2. These anomalous Hall crystals are incommensurate with the moir\'e superlattice and exhibit dispersive fan diagrams consistent with the Streda formula, with their positions continuously tunable through displacement fields. Remarkably, these partially filled Chern insulators display Chern numbers distinct from their parent bands. Our findings demonstrate the rich variety of electronic crystalline states in rhombohedral graphene moir\'e superlattices, offering valuable insights into the strongly correlated topological phases.