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We report far-infrared magnetoabsorption measurements of thin graphite samples exfoliated from highly ordered pyrolytic graphite showing transitions originating from the K and the H points. For the K point, both cyclotron resonance and interband transitions are measured which are not described well by the currently accepted values of the parameters in the Slonczewski-Weiss-McClure tight-binding model. We demonstrate that the observed data can be better described using an effective bilayer graphite model which has been modified to include an electron-hole asymmetry.

Energy loss rates for hot carriers in graphene have been measured using graphene produced by epitaxial growth on SiC, exfoliation, and chemical vapor deposition (CVD). It is shown that the temperature dependence of the energy loss rates measured with high-field damped Shubnikov-de Haas oscillations and the temperature dependence of the weak localization peak close to zero field correlate well, with the high-field measurements understating the energy loss rates by ∼40% compared to the low-field results. The energy loss rates for all graphene samples follow a universal scaling of T 4 e at low temperatures and depend weakly on carrier density ∝n − 1 2 , evidence for enhancement of the energy loss rate due to disorder in CVD samples.

Weak localization in graphene is studied as a function of carrier density in the range from 1 × 10 11 cm −2 to 1.43 × 10 13 cm −2 using devices produced by epitaxial growth onto SiC and CVD growth on thin metal film. The magnetic field dependent weak localization is found to be well fitted by theory, which is then used to analyze the dependence of the scattering lengths L ϕ , L i , and L * on carrier density. We find no significant carrier dependence for L ϕ , a weak decrease for L i with increasing carrier density just beyond a large standard error, and a n −1/4 dependence for L * . We demonstrate that currents as low as 0.01 nA are required in smaller devices to avoid hot-electron artifacts in measurements of the quantum corrections to conductivity.

We report the phase space defined by the quantum Hall effect breakdown in polymer gated epitaxial graphene on SiC (SiC/G) as a function of temperature, current, carrier density, and magnetic fields up to 30 T. At 2 K, breakdown currents (I(c)) almost 2 orders of magnitude greater than in GaAs devices are observed. The phase boundary of the dissipationless state (ρ(xx)=0) shows a [1-(T/T(c))2] dependence and persists up to T(c)>45  K at 29 T. With magnetic field I(c) was found to increase ∝B(3/2) and T(c)∝B2. As the Fermi energy pproaches the Dirac point, the ν=2 quantized Hall plateau appears continuously from fields as low as 1 T up to at least 19 T due to a strong magnetic field dependence of the carrier density.