Zero-energy state in graphene in a high magnetic field

The fate of the charge-neutral Dirac point in graphene in a high magnetic field H has been investigated at low temperatures (T similar to 0.3 K). In samples with small gate-voltage offset V(0), the resistance R(0) at the Dirac point diverges steeply with H, signaling a crossover to a state with a very large R(0). The approach to this state is highly unusual. Despite the steep divergence in R(0), the profile of R(0) vs T in fixed H saturates to a T-independent value below 2 K, consistent with gapless charge-carrying excitations.