Anomalous quantum Hall effect in charge-density-wave material η-Mo₄O₁₁

We have performed magnetotransport experiments for η-Mo₄O₁₁ from 80 mK to 1.5 K and up to 55 T by means of edge contact method and using a pulsed magnet. In the intermediate field range of 10 < B < 25 T, we have observed anomalous quantum Hall effect, where the values of the Hall resistivity ρ_H at flat plateaus rather decreases, suggesting the order of the filling factor ν = 2 → 3 → 4. We proposed a possible model based on a field-dependent Fermi surface. Above 25 T, furthermore, we have observed broad peaks in both ρ-B and ρ_H-B curves.