The conductivity of graphene samples with various levels of disorder is investigated for a set of specimens with mobility in the range of $1–20\times {10}^3{\mathrm{cm}}^2/\mathrm{V}\sec$. Comparing the experimental data with the theoretical transport calculations based on charged impurity scattering, we estimate that the impurity concentration in the samples varies from $2–15\times {10}^{11}{\mathrm{cm}}^{-2}$. In the low carrier density limit, the conductivity exhibits values in the range of $2–12e^2/h$, which can be related to the residual density induced by the inhomogeneous charge distribution in the samples. The shape of the conductivity curves indicates that high mobility samples contain some short-range disorder whereas low mobility samples are dominated by long-range scatterers.

A circular route to confine electrons: Physical barriers are used to confine waves. Whether it is harbor walls for sea waves, a glass disk for light, or the “whispering gallery” circular chamber walls in St. Paul's Cathedral for sound, the principle of confinement—reflection—is the same. Zhao et al. used that same principle to confine electrons in a nanoscale circular cavity in graphene. Periodic patterns within the cavity were associated with an electronic wave version of whispering gallery modes. The tunability of the cavity size may provide a route for the manipulation of electrons in graphene and similar materials. Science , this issue p. 672

The quantum Hall effect near the charge neutrality point in bilayer graphene is investigated in high magnetic fields of up to 35~T using electronic transport measurements. In the high-field regime, the eightfold degeneracy in the zero-energy Landau level is completely lifted, exhibiting new quantum Hall states corresponding to filling factors $\nu${}=0, 1, 2, and 3. Measurements of the activation energy gaps for the $\nu${}=2 and 3 filling factors in tilted magnetic fields exhibit no appreciable dependence on the in-plane magnetic field, suggesting that these Landau level splittings are independent of spin. In addition, measurements taken at the $\nu${}=0 charge neutral point show that, similar to single layer graphene, the bilayer becomes insulating at high fields.