Observation of Fractional Quantum Anomalous Hall Effect

The interplay of topology, magnetism, and strong correlation leads to intriguing quantum states of matter. A prominent example is the quantum anomalous Hall effect (QAHE), which displays integer quantum Hall effect at zero magnetic field due to topologically nontrivial bands and intrinsic magnetism. Realizing a similar analogue of the fractional quantum Hall effect at zero field, known as the fractional quantum anomalous Hall effect (FQAHE), has long posed a challenge due to stringent constraints in electron-electron interaction and quantum geometry. Here, we present the experimental observation of FQAHE and electrically tunable topological phase transition in twisted MoTe2 bilayer using electrical transport measurements. In addition, an anomalous Hall state emerges near the filling factor -1/2. Its behavior mirrors that of the composite Fermi liquid in the half-filled lowest Landau level of a two-dimensional electron gas under high magnetic fields. The direct observation of the FQAH and associated effects opens the door to exploring charge fractionalization and anyonic statistics at zero magnetic field.