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 approximate to 1/2. Backscattering in this system involves spin flip, so that interaction with localized magnetic moments generates a finite resistivity R-xx via a chiral Kondo effect. At finite temperatures T, R-xx(T) exhibits a crossover from metallic to insulating behavior as K is tuned across a threshold K-MI. For T -> 0, R-xx 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.