We have performed magnetotransport measurements on a multi-layer graphene flake. At the crossing magnetic field Bc, an approximately temperature-independent point in the measured longitudinal resistivity xx, which is ascribed to the direct insulator-quantum Hall (I-QH) transition, is observed. By analyzing the amplitudes of the magnetoresistivity oscillations, we are able to measure the quantum mobility μqof our device. It is found that at the direct I-QH transition, μqBc≈ 0.37 which is considerably smaller than 1. In contrast, at Bc, xxis close to the Hall resistivity xy, i.e., the classical mobility μBcis ≈ 1. Therefore, our results suggest that different mobilities need to be introduced for the direct I-QH transition observed in multi-layered graphene. Combined with existing experimental results obtained in various material systems, our data obtained on graphene suggest that the direct I-QH transition is a universal effect in 2D.
- Graphene flake
- Insulator-quantum hall transition
- Multi-layer grapheme