Abstract
We studied the unusual quantum Hall effect (QHE) near the charge neutrality point in high-mobility graphene sample for magnetic fields up to 18 T. We observe breakdown of the delocalized QHE transport and strong increase in resistivities with decreasing Landau-level filling for , where we identify two insulating regimes. First, increases nearly exponentially within the range of several resistance quanta , while the Hall effect gradually disappears and the off-diagonal resistivity eventually becomes independent of the direction of magnetic field, consistent with the Hall insulator with local transport. Then, at a filling , there is a cusp in and an onset of even faster growth with the decreasing , indicating transition to a collective insulator state. A likely candidate for this state is a pinned Wigner crystal.
- Received 13 April 2009
DOI:https://doi.org/10.1103/PhysRevB.80.241412
©2009 American Physical Society