Abstract:
Neutral graphene in a magnetic field exhibits an unexpected insulating state and a missing quantum Hall plateau. Electrons in graphene in a magnetic field has 2N_B fold degenerate n = 0 single particle Landau levels from two valleys and exactly 2N_B spinful electrons. Here N_B is the number of elementary magnetic flux quanta threading the sample. We develop a microscopic theory where, at low energy scales, a complete set of 2N_B single particle Landau-Gaussian orbitals forming a \texit{Von Neuman lattice} have single electron occupancy and dangling spins. Certain novel superexchange interactions among spins destabilise the exchange induced quantum Hall ferromagnetism and decouples spin from charge and organize spins into a chiral spin liquid state. Charged excitations have a Mott gap and spin excitations are either gapless or have a smaller gap. Spin charge separation removes edge channels for spinful electrons and prevents Hall plateau formation.