Unique One- and Two-Dimensional Phenomena Observed in Carbon Nanotubes and Graphene

Metallic single-walled carbon nanotubes (SWNTs) provide an excellent system for studying interesting one-dimensional physics, including exceptionally strong electron-phonon coupling, Kohn anomalies, ballistic electron transport, and strongly correlated electrons. In this presentation, I will report measurements of nearly defect free, suspended carbon nanotubes under high voltage biases. Raman spectroscopy reveals exceptionally strong electron-phonon coupling, arising from Kohn anomalies, which result in mode selective electron-phonon coupling, negative differential conductance (NDC), and non-equilibrium phonon populations[l,2]. Due to the extremely long electron lifetimes, we observe a breakdown of the Born-Oppenheimer approximation, as deduced from the gate voltage induced changes in the vibrational energies of suspended carbon nanotubes[3]. Spatially-resolved temperature measurements of carbon nanotubes under high applied bias voltages reveal a unique thermal conduction mechanism that is quite different from bulk materials, and enables these nanotube devices to operate at extremely high power densities[4]. We also report strikingly large variations in the Raman intensity of pristine metallic SWNTs in response to gate voltages, which are attributed to a Mott insulating state of the strongly correlated electrons[5]. Lastly, we observe the formation of periodic ripples in suspended graphene, which arise from a large mismatch in compressive strain between the substrate and suspended regions[6].