Magic-angle twisted bilayer graphene (MATBG) hosts a multitude of strongly correlated states at partial fillings of its flat bands. In a magnetic field, these flat bands further evolve into a unique Hofstadter spectrum renormalized by strong Coulomb interactions. Here, we study the interacting Hofstadter states spontaneously formed within the topological magnetic subbands of an ultraclean MATBG device, notably including symmetry-broken Chern insulator (SBCI) states and fractional quantum Hall (FQH) states. The observed SBCI states form a cascade with their Chern numbers mimicking the main sequence correlated Chern insulators. The FQH states in MATBG form in Jain sequence; however, they disappear at high magnetic field, distinct from conventional FQH states which strengthen with increasing magnetic field. We reveal a unique magnetic field-driven phase transition from composite fermion phases to a dissipative Fermi liquid. Our theoretical analysis of the magnetic subbands hosting FQH states predicts non uniform quantum geometric properties far from the lowest Landau level. This points towards a more natural interpretation of these FQH states as in-field fractional Chern insulators of the magnetic subbands.
@article{arxiv.2408.01599,
title = {Strongly interacting Hofstadter states in magic-angle twisted bilayer graphene},
author = {Minhao He and Xiaoyu Wang and Jiaqi Cai and Jonah Herzog-Arbeitman and Takashi Taniguchi and Kenji Watanabe and Ady Stern and B. Andrei Bernevig and Matthew Yankowitz and Oskar Vafek and Xiaodong Xu},
journal= {arXiv preprint arXiv:2408.01599},
year = {2025}
}