Figure 1: Graphene on SiC and the experimental techniques.

(a) Atomic force microscopy phase image of graphene on SiC (ref. 27). Scale bar, 1 μm. Single-layer graphene (brown colour in majority regions) covers the substrate, while two or more graphene layers (yellow colour in minority regions) are formed along the terrace edge. As few-layer graphene regions are fragmented, the single-layer graphene dominates carrier transport. (b) R_xx and R_xy at 1.5 K of a Hall bar device with the channel width and length of 0.2 and 1.1 mm, respectively. The mobility is 12,000 cm² V⁻¹s⁻¹. (c) Schematic illustration (not to scale) of the sample structure and the experimental setup for the time-resolved transport measurement. (d) Voltage step with the height of 1 V and the time width of 50 ns applied to the injection gate (top) and temporal traces of the current detected by a sampling oscilloscope (bottom). The current is averaged over a few seconds on the period of the excitation voltage step. Small features around −10 and 40 ns are due to reflections in high-frequency lines. Inset shows the magnified view of the current trace around t=0. The sharp peak at t=0 is due to direct cross-talk between high-frequency lines. The broad peak indicated by an arrow is due to the charge pulse arriving at the detector Ohmic contact.