Terahertz and Infrared Conductivity of Large-Area Graphene

Graphene is predicted to offer new opportunities for terahertz (THz) science and technology. Its zero-gap linear band dispersion is expected to lead to exotic nonlinear electromagnetic properties, which can be probed through frequency-dependent conductivity measurements. Here, we use THz time-domain spectroscopy and Fourier-transform infrared spectroscopy to investigate carrier dynamics in large-area graphene grown by chemical vapor deposition. We studied both nitrogen-doped and nominally-undoped graphene; the latter had accidental doping presumably through air and acid exposure. Absorption increased with the number of graphene layers and was larger in the nominally-undoped samples especially in the 0.2-2.2 THz range. For the highest-mobility samples, we observed Drude-like frequency dependence in the THz range. Further measurements in a wider spectral range are in progress to understand the differences between these samples and the interplay between intra-band and inter-band dynamics.