Terahertz and Ultrafast Dynamics of Carriers and Phonons in Graphene and Carbon Nanotubes

Graphene and carbon nanotubes provide a variety of new opportunities for fundamental and applied research. Here, we describe results of our recent terahertz and ultrafast studies of carriers and phonons in these materials. Time-domain terahertz spectroscopy is a powerful method for determining the basic properties of charge carriers in a non-contact manner. We show how one can modulate the transmission of terahertz waves through graphene by gating and how one can improve the modulation performance by combining graphene with apertures and gratings. In carbon nanotubes, we demonstrate that the terahertz response is dominated by plasmon oscillations, which are enhanced by collective antenna effects when the nanotubes are aligned. Finally, ultrafast spectroscopy of carbon nanotubes allow us to excite and probe coherent phonons, both in the low-energy radial breathing mode and high-energy G-mode, which are strongly coupled with excitonic interband transitions.