Coherently Controlled Ballistic Charge Currents Injected in Single-Walled Carbon Nanotubes and Graphite

Ballistic electrical currents are optically injected into aligned single-walled carbon nanotubes and bulk graphite at 300 K via quantum interference between single and two photon absorption of phase-related 700 and 1400 nm, 150 fs pulses. The transient currents are detected via the emitted terahertz radiation. Optical phase and power dependence are consistent with the quantum interference optical process. Under similar excitation conditions, the peak current for a forest of nanotubes, with a diameter distribution of ∼2.5 ( 1.5 nm, is 9 ( 1 times larger than that in graphite. At peak focused intensities of 10 GW cm-2 (1400 nm) and 0.15 GW cm-2 (700 nm), the peak current is ∼1 nA per nanotube. The peak current for pump light polarized along the tubes is ∼3.5 times higher than that for light polarized perpendicular to the tubes. Since their discovery in the early 1990s, carbon nano-structures have received considerable research attention because of their unique physical and electronic properties and their potential applications in nanotechnology.1 In particular, carbon nanotubes and graphene are thought to represent important basic building blocks for future devices because of their unique electron transport properties related to their band structure and low carrier scattering rates