Modeling light-assisted nano-junctions and interfaces
Ines Urdaneta
ISMO, Orsay et LCT, Université Pierre et Marie Curie, Paris, France
Vendredi 21 Juin 2013, 14h00
bibliothèque LCT, tour 12 - 13, 4e étage
A theoretical description of laser-assisted electron transport in nano-junctions (molecule or atom between two metallic electrodes represented by a free electron gas) is presented. Transport occurs under the combined influence of a static voltage bias and a time-dependent field representing the laser. The calculation is carried out at the one-electron level both in the description of the molecular structure and also in the computation of the current itself. This relatively simple model captures the essence of the transport phenomena in presence of static and oscillating electric fields.
The current is computed within a Landauer approach as a scattering process combined with a Floquet transformation to include the effects of the time-dependent field. Two different methodologies are used to compute the current: One that involves a discrete representation (tight-binding) model for a molecule, used for low voltage and intensity domain, and another where the entire system is considered as a single entity (wave function approach) and an atom is represented by a potential well resonance, used for higher laser intensity fields and where non-linear effects are predominant. An analysis, in terms of the binding state energies and width, and their incidence over the nonlinear and nonpertubative regimes observed on the current, advocated also an interpretation in terms of interference between two pathways (one occurring when the radiation field affects the atom and the interfaces atom-metals, and the other one when only the atom is illuminated).
Computing the current in the Floquet scheme is pertinent since it has been verified that the Floquet current corresponds to the Fourier component of the Keldysh (non-equilibrium Green's funtion) dc current.