We report a change of three orders of magnitude in the resistance of a suspended bilayer graphene flake which varies from a few k in the high-carrier-density regime to several M around the charge neutrality point (CNP). The corresponding transport gap is 8 meV at 0.3 K. The sequence of quantum Hall plateaus appearing at filling factor ν = 2 followed by ν = 1 suggests that the observed gap is caused by the symmetry breaking of the lowest Landau level. Investigation of the gap in a tilted magnetic fields indicates that the resistance at the CNP shows a weak linear decrease for increasing total magnetic field. Those observations are in agreement with a spontaneous valley splitting at zero magnetic field followed by splitting of the spins originating from different valleys with increasing magnetic field. Both the transport gap and B field response point toward the spin-polarized layer-antiferromagnetic state as the ground state in the bilayer graphene sample. The observed nontrivial dependence of the gap value on the normal component of B suggests possible exchange mechanisms in the system.

We have measured the spin splitting in single-layer and bilayer graphene by means of tilted magnetic field experiments. Applying the Lifshitz-Kosevich formula for the spin-induced decrease of the Shubnikov de Haas amplitudes with increasing tilt angle we directly determine the product between the carrier cyclotron mass m * and the effective g-factor g * as a function of the charge carrier concentration. Using the cyclotron mass for a single-layer and a bilayer graphene we find an enhanced g-factor g * = 2.7 ± 0.2 for both systems. arXiv:1107.3925v2 [cond-mat.mes-hall]

The quantum Hall effect is a remarkable manifestation of quantized transport in a two-dimensional electron gas. Given its technological relevance, it is important to understand its development in realistic nanoscale devices. In this work we present how the appearance of different edge channels in a field-effect device is influenced by the inhomogeneous capacitance profile existing near the sample edges, a condition of particular relevance for graphene. We apply this practical idea to experiments on high quality graphene, demonstrating the potential of quantum Hall transport as a spatially resolved probe of density profiles near the edge of this two-dimensional electron gas.

Magneto-transport experiments on ABC-stacked suspended trilayer graphene reveal a complete splitting of the twelve-fold degenerated lowest Landau level, and, in particular, the opening of an exchange-driven gap at the charge neutrality point. A quantitative analysis of distinctness of the quantum Hall plateaus as a function of field yields a hierarchy of the filling factors: \nu=6, 4, and 0 are the most pronounced, followed by \nu=3, and finally \nu=1, 2 and 5. Apart from the appearance of a \nu=4 state, which is probably caused by a layer asymmetry, this sequence is in agreement with Hund's rules for ABC-stacked trilayer graphene

Field-induced quantum Hall ferromagnetism in suspended bilayer graphene van Elferen, H. J.; Veligura, A.; Kurganova, E. V.; Zeitler, U.; Maan, J. C.; Tombros, N.; VeraMarun, I. J.; van Wees, B. J. We have measured the magnetoresistance of freely suspended high-mobility bilayer graphene. For magnetic fields B > 1 T we observe the opening of a field-induced gap at the charge neutrality point characterized by a diverging resistance. For higher fields the eightfold degenerated lowest Landau level lifts completely. Both the sequence of this symmetry breaking and the strong transition of the gap-size point to a ferromagnetic nature of the insulating phase developing at the charge neutrality point.