Coherent control of photocurrents in graphene and carbon nanotubes

Abstract

Coherent one photon (2ω) and two photon (ω) electronic excitations are studied for graphene sheets and for carbon nanotubes using a long wavelength theory for the low energy electronic states. For graphene sheets we find that coherent superposition of these excitations produces a polar asymmetry in the momentum space distribution of the excited carriers with an angular dependence which depends on the relative polarization and phases of the incident fields. For semiconducting nanotubes we find a similar effect which depends on the square of the semiconducting gap, and we calculate its frequency dependence. We find that the third order nonlinearity which controls the direction of the photocurrent is robust for semiconducting tubes and vanishes in the continuum theory for conducting tubes. We calculate corrections to these results arising from higher order crystal field effects on the band structure and briefly discuss some applications of the theory.

Controllable unzipping for intramolecular junctions of graphene nanoribbons and single-walled carbon nanotubes

“…More importantly, excitons are expected to form in the bulk sections of the 1D structure because of strong 2D quantum confinement, and thus a much enhanced Coulombic electron-hole coupling was observed in the cross-section. Consequently, the optical absorption probability, the driftdiffusion velocity of the carriers, and the carrier relaxation time notably increases 37,[41][42][43][44] . These, as well as the high efficiency for electron-hole separation at the SWNT/GNR junction, give rise to a strong photo-response.…”

Electromagnetic-Field-Induced Suppression of Transport throughn−pJunctions in Graphene

“…The externally applied EF is taken into account in the two bands time and coordinate dependent Hamiltonian of the n-p junction as follows [14]:…”

An Approach To “Quantumness” In Coherent Control

“…For example, the path alternatives are given by the two excitation processes in a 1 vs. N coherent control scenario. The resultant CCI framework is general and applicable to many systems, from atoms [15,66] to molecules [27,45,[67][68][69] to bulk solids [4,5,20,30,[70][71][72][73][74][75]. Further, the control field can be in a semiclassical coherent or in a quantum state of light, such as a multimode Fock state or a squeezed state.…”