We studied the unusual Quantum Hall Effect (QHE) near the charge neutrality point (CNP) 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 ρxx,∣ρxy∣ with decreasing Landau level filling for ν<2, where we identify two insulating regimes. For 1≳∣ν∣≳1/2 we find an exponential increase of ρxx,xy∼ea(H−Hc) within the range up to several resistance quanta RK, while the Hall effect gradually disappears, consistent with the Hall insulator (HI) with local transport. Then, at ν≈1/2 a cusp in ρxx(H) followed by an onset of even faster growth indicates transition to a collective insulator (CI) state. The likely candidate for this state is a pinned Wigner crystal.
@article{arxiv.0904.1996,
title = {Breakdown of the N=0 Quantum Hall State in graphene: two insulating regimes},
author = {L. Zhang and J. Camacho and H. Cao and Y. P. Chen and M. Khodas and D. Kharzeev and A. Tsvelik and T. Valla and I. A. Zaliznyak},
journal= {arXiv preprint arXiv:0904.1996},
year = {2010}
}