Quantum Hall States near the Charge-Neutral Dirac Point in Graphene

1. Quantum Hall States near the Charge-Neutral Dirac Point in Graphene PI: Philip Kim, Department of Physics, Columbia University Supported by NSF (No. DMR-03-52738 and No. CHE-0117752) DOE (No. DE-AIO2-04ER46133 and No. DE-FG02-05ER46215) ONR (No. N000150610138), NYSTAR, Keck Foundation, and Microsoft Project Q The experimental observation of the quantum Hall (QH) effect in single atomic sheet of graphene has attracted much attention recently, particularly due to the unique electronic transport observed in this material. In our work, weinvestigate the QH states near the charge-neutral Diracpoint of a high mobility graphene sample in high magneticfields. We find that the QH states at filling factors  depend only on the perpendicular component of the fieldwith respect to the graphene plane, indicating that they arenot spin related. A square root magnetic field dependence of theactivation energy gap at filling factor  suggests a many-bodyorigin. We therefore propose that the 0 and  statesarise from the lifting of the spin and sublattice degeneracyof the n=0 Landau level, respectively. Figure: Magnetoresistance (Rxx) as a function of back gate voltage (Vg) in tilted magnetic fields. Jiang, Z.; Zhang, Y.; Stormer, H.L.; and Kim, P.,Phys. Rev. Lett., 99 (10), 106802 (2007). NHMFL