14 research outputs found
Transport Gap in Suspended Bilayer Graphene at Zero Magnetic Field
We report a change of three orders of magnitudes in the resistance of a
suspended bilayer graphene flake which varies from a few ks in the high
carrier density regime to several Ms around the charge neutrality point
(CNP). The corresponding transport gap is 8 meV at 0.3 K. The sequence of
appearing quantum Hall plateaus at filling factor followed by
suggests that the observed gap is caused by the symmetry breaking of the lowest
Landau level. Investigation of the gap in a tilted magnetic field 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 field response point toward spin polarized layer
antiferromagnetic state as a ground state in the bilayer graphene sample. The
observed non-trivial dependence of the gap value on the normal component of
suggests possible exchange mechanisms in the system.Comment: 8 pages, 5 figure
Field induced quantum-Hall ferromagnetism in suspended bilayer graphene
We have measured the magneto-resistance of freely suspended high-mobility
bilayer graphene. For magnetic fields T we observe the opening of a field
induced gap at the charge neutrality point characterized by a diverging
resistance. For higher fields the eight-fold 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.Comment: 7 pages, 5 figure
Coexistence of electron and hole transport in graphene
When sweeping the carrier concentration in monolayer graphene through the
charge neutrality point, the experimentally measured Hall resistivity shows a
smooth zero crossing. Using a two- component model of coexisting electrons and
holes around the charge neutrality point, we unambiguously show that both types
of carriers are simultaneously present. For high magnetic fields up to 30 T the
electron and hole concentrations at the charge neutrality point increase with
the degeneracy of the zero-energy Landau level which implies a quantum Hall
metal state at \nu=0 made up by both electrons and holes.Comment: 5 pages, 6 figure
Fine structure of the lowest Landau level in suspended trilayer graphene
<p>Magnetotransport experiments on ABC-stacked suspended trilayer graphene reveal a complete splitting of the 12-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.</p>
Quantum Hall transport as a probe of capacitance profile at graphene edges
<p>The quantum Hall effect is a remarkable manifestation of quantized transport in a two-dimensional electron gas (2DEG). 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. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773589]</p>
Spin splitting in graphene studied by means of tilted magnetic-field experiments
We have measured the spin splitting in single-layer and bilayer graphene by means of tilted magnetic-field experiments. By 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. By 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.