Physics Colloquium - McMillan Award Winner - Zhengguang Lu 11/19/2025

Title: “’Fractional Quantum Anomalous Hall Effects in Rhombohedral Graphenev”

Abstract: The fractional quantum Hall (FQH) effect, driven by strong correlations in Landau levels, has long stood as a paradigm of emergent topological order and fractionalized quasiparticles with potential applications in quantum computation. A long-standing goal has been to realize its zero-field counterpart, the fractional quantum anomalous Hall (FQAH) effect, which is predicted to arise in topological flat bands through interaction-induced breaking of time-reversal symmetry. Here we report the observation of integer and fractional quantum anomalous Hall effects in rhombohedral multilayer graphene/hBN moiré superlattices. At zero magnetic field, in addition to a C = 1 quantum anomalous Hall state, we observe eleven fractionally quantized Hall resistance plateaus Rxy=h/(νe2) at filling factors including ν=2/3, 3/5, 4/7… 4/9, 3/7, and 1/3. Near half-filling, the Hall resistance varies linearly with carrier density and approaches Rxy=2h/e2, reminiscent of the composite Fermi liquid in the half-filled Landau level. Most notably, further experiments reveal the coexistence of FQAH states, electron crystallization, and superconductivity at lower electron temperatures. Together, these results establish rhombohedral graphene moiré superlattices as a versatile platform for realizing exotic correlated topological phases and for exploring quasiparticles with fractional statistics, ultimately advancing toward non-Abelian anyons, key building blocks for universal, fault-tolerant quantum computation.