Terahertz-frequency electronic transport in graphene

We calculate the room-temperature complex conductivity [sigma]( omega ) of suspended and supported graphene at terahertz frequencies (100 GHz-10 THz) by employing a self-consistent coupled simulation of carrier transport and electrodynamics. We consider a wide range of electron (n = 10 super(12)-10 super(13) cm super(-2)) and impurity (N sub(i) = 8 x 10 super(10)-2 x 10 super(12) cm super(-2)) densities. For graphene supported on SiO sub(2), there is excellent agreement between the calculation with clustered impurities and the experimentally measured [sigma]( omega ). The choice of substrate (SiO sub(2) or h-BN) is important at frequencies below 4 THz. We show that carrier scattering with substrate phonons governs transport in supported graphene for N sub(i)/n < 0.1. Electron-impurity interactions dominate for N sub(i)/n > 0.1, and transport enters the electron-hole puddle regime for N sub(i)/n > 0.5. The simple Drude model, with an effective scattering rate [Gamma] and Drude weight D as parameters, fits the calculated [sigma]( omega ) for supported graphene very well, owing to electron-impurity scattering. [Gamma] decreases with increasing n faster than n super(-1/2) and is insensitive to electron-electron interaction. Both electron-electron and electron-impurity interactions reduce the Drude weight D, and its dependence on n is sublinear.