Insulating behavior at the neutrality point in dual-gated, single-layer graphene

F. Amet, J. R. Williams, K. Watanabe, T. Taniguchi, D. Goldhaber-Gordon

Published 2012-09-27, updated 2013-01-15Version 2

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.