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

We have performed magnetotransport experiments for eta -Mo4O11 from 80 mK t o 1.5 K and up to 55T by means of edge contact method and using a pulsed ma gnet. In the intermediate field range of 10 < B < 25 T, we have observed an omalous quantum Hall effect, where the Values of the Hall resistivity p, at flat plateaus rather decreases, suggesting the order of the filling factor v = 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 bo th rho -B and rho (H)-B curves. (C) 2001 Elsevier Science B.V. All rights r eserved.