Observation of dissipationless fractional Chern insulator

The fractional quantum anomalous Hall effect has recently been experimentally observed in fractional Chern insulators at zero magnetic field. However, an outstanding challenge is the presence of substantial longitudinal resistance, even though the anomalous Hall resistance is quantized. This dissipation is probably linked to imperfect sample quality. Here we demonstrate a twisted MoTe₂ bilayer device that exhibits quantized anomalous Hall resistance and vanishing longitudinal resistance for the fractional state, such that it is a dissipationless fractional Chern insulator. Unlike fractional quantum Hall states, where the energy gap increases with magnetic field, the thermal activation gap of the fractional state decreases rapidly with magnetic field and then plateaus above a few teslas. This behaviour reflects the coexistence of two distinct excitation channels: spinful quasiparticles dominate transport at low magnetic fields whereas spinless quasiparticles govern transport at high fields, where Zeeman splitting suppresses spin-flip processes. Our results provide insights into the energy scale of fractional Chern insulators and indicate a pathway to the quantum engineering of exotic correlated topological states.