Figure 4

Fig. 4. (A) Schematic of the 2D Brillouin zone (blue lines), constantenergy contours (green rings) at the K_± points, and the two dominant classes of scattering vectors that create the interference patterns. k₁ and k₂ denote the wave vectors of incident and scattered carriers. Scattering wave vectors q₁ (short red arrow) are seen to connect points on a single constant-energy circle, and wave vectors q₂ (long red arrow) connect points on constant-energy circles between adjacent K₊ and K_– points. Red circles indicate graphene reciprocal lattice points with origin . (B) q-space map of scattering amplitudes, obtained from the Fourier transform power spectrum of the dI/dV map in Fig. 2D. q₁ scattering forms the small ring at q = 0, whereas q₂ events create the six circular disks at K_± points. (C) Angular averages of the central q₁ ring from the q-space maps, at bias voltages from –100 to –20 mV shown in 10-mV increments, arb., arbitrary units. (D) Energy dispersion as a function of for bilayer graphene determined from the q-space profiles in (C) and similar data. Values shown are derived from the radii of the central q₁ scattering rings (red squares) and from the angle-averaged radii of the scattering disks at K₊ and K_– (blue triangles). Dashed line shows a linear fit to the data with v_F = (9.7±0.6) x 10⁵ m/s and an energy intercept of –330 ± 20 meV. Similar results are found for a single monolayer of graphene (fig. S2D) (18). The error bars represent the typical combined statistical and systematic uncertainties estimated for each data set. [View Larger Version of this Image (382K JPEG file)]

 

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