* Title : Mott-Hall Insulator and Chiral Spin Liquid Phase in Neutral Graphene in a Magnetic Field

* Speaker: Prof. Ganapathy Baskaran (Institute of Mathematical Sciences)

* Date & Time: Dec. 2 (Wed) 16:30

* Place: #512, Hogil Kim Memorial Bldg., POSTECH

* Abstract:

Neutral graphene in a magnetic field exhibits an unexpected insulating phase 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 exit{Von Neuman lattice} have single electron occupancy and dangling spins. Certain novel superexchange interaction among spins destabilise the exchange induced quantum Hall ferromagnetism, decouple 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.