The fate of the low-temperature conductance at the charge-neutrality (Dirac) point in a single sheet of graphene is investigated down to 20 mK. As the temperature is lowered, the peak resistivity diverges with a power-law behavior and becomes as high as several Megohms per square at the lowest temperature, in contrast with the commonly observed saturation of the conductivity. As a perpendicular magnetic field is applied, our device remains insulating and directly transitions to the broken-valley-symmetry, nu=0 quantum Hall state, indicating that the insulating behavior we observe at zero magnetic field is a result of broken valley symmetry. Finally we discuss the possible origins of this effect.
@article{arxiv.1209.6364,
title = {Insulating behavior at the neutrality point in dual-gated, single-layer graphene},
author = {F. Amet and J. R. Williams and K. Watanabe and T. Taniguchi and D. Goldhaber-Gordon},
journal= {arXiv preprint arXiv:1209.6364},
year = {2014}
}