Onset of an insulating zero-plateau quantum Hall state in graphene

We analyze the dissipative conductance of the zero-plateau quantum Hall state appearing in undoped graphene in strong magnetic fields. Charge transport in this state is assumed to be carried by a magnetic domain wall, which forms by hybridization of two counterpropagating edge states of opposing spin due to interactions. The resulting nonchiral edge mode is a Luttinger liquid of parameter K, which enters a gapped, perfectly conducting state below a critical value K_{c} approximately 1/2. Backscattering in this system involves spin flip, so that interaction with localized magnetic moments generates a finite resistivity Rxx via a "chiral Kondo effect." At finite temperatures T, Rxx(T) exhibits a crossover from metallic to insulating behavior as K is tuned across a threshold K_{MI}. For T --> 0, Rxx in the intermediate regime K_{MI} < K < K_{c} is finite, but diverges as K approaches K_{c}. This model provides a natural interpretation of recent experiments.