Extended fractional Hofstadter states at high field in twisted bilayer graphene above the magic angle

When a Chern band is partially filled, a fractional Chern insulator (FCI)—the lattice analog of a fractional quantum Hall state—can arise. Though the full range of possible scenarios for producing such a state is not established, the most tractable models combine strong electronic interactions with the quantum geometry of the parent Chern band meeting specific criteria. In twisted bilayer graphene, the importance of interactions can be tuned by varying the interlayer twist. Here, we study a sample with twist near 1.4 ° , large enough to suppress the zero-field correlated states. We find that applying a strong magnetic field restores the importance of electron–electron interactions: at nearly half a magnetic flux quantum per moiré unit cell, deep in the Hofstadter regime, odd-denominator fractional states appear in multiple Hofstadter subbands. These fractional states persist over larger ranges of density, and are more robustly quantized, than nearby integer states, opposite to what is seen in other fractional quantum Hall and FCI systems.