Surface Transport in the ν=0 Quantum Hall Ferromagnetic State in the Organic Dirac Fermion System

We discuss the surface magnetotransport in the quantum Hall (QH) ferromagnetic state expected in the organic Dirac fermion system \alpha-(BEDT-TTF)_2I_3. The QH ferromagnetic state is one of the possible \nu=0 QH states in the two-dimensional Dirac fermion system resulting from the degeneracy breaking of the n=0 Landau level. It is characterized by the helical edge state. We have studied the interlayer surface transport via helical edge state in the multilayer QH ferromagnet, in which the bulk region is insulating. We have clarified that the surface conductivity is much less than e^2/h and decreases as the magnetic field is tilted to the normal direction of the side surface. These features explain the observed interlayer magnetoresistance in \alpha-(BEDT-TTF)_2I_3.