The Direct Insulator-Quantum Hall Transition

The direct insulator-quantum Hall (I-QH) transition corresponds to a transition from an insulator to a high Landau-level-filling factor nu > 2 QH state, which is characterized by an approximately temperature T-independent longitudinal resistance of a few nm thick electron (or hole) layer. In this paper, we review both the experimental and theoretical results on the direct I-QH transition. In particular, we attempt to address several interesting yet unsettled issues in the field of the direct I-Q transition. We suggest that further studies are required for obtaining a thorough understanding of the direct I-QH transition observed in nano-scale charge layers.