MIT News  November 18, 2024 Recent experiments on the moiré structure formed by pentalayer rhombohedral graphene aligned with a hexagonal boron nitride substrate report the discovery of a zero-field fractional quantum Hall effect. These “(fractional) quantum anomalous Hall” [(F)QAH] phases occur for one sign of a perpendicular displacement field, and correspond, experimentally, to full or partial filling of a valley polarized Chern-1 band. Such a band is absent in the noninteracting band structure. Researchers at MIT showed that electron-electron interactions play a crucial role, and presented microscopic theoretical calculations demonstrating the emergence of a nearly flat, isolated, Chern-1 band and […]