Optical absorption and emission of a quantum dot in the Kondo regime

Abstract

A variant of the Anderson model, that describes hybridization between localized state (c-state) of a quantum dot and a Fermi sea conduction band, is investigated. We demonstrate that, as a function of the hybridization parameter v, the system undergoes a crossover from the state where the conduction band and the c-level are fully coupled to a state where these are decoupled. The c-electron spectrum, however, has a gap together with the presence of the Kondo peak in the former state. For the latter, we have a Mott-like localization where the c-electron spectrum again has a gap without the Kondo peak. Within this gap the conduction electrons fully recover the free band density of states and the effective hybridization is practically zero. Our main aim, however, is to study the emission and absorption in a quantum dot with strongly correlated Kondo ground state. We use the Green function equation of motion method for this purpose. We calculate the absorption/emission (A/E) spectrum in the Kondo regime through a symmetrized quantum autocorrelation function obtainable directly within perturbation theory using the Fermi golden rule approximation. The spectrum reveals a sharp, tall peak close to Kondo-Abrikosov-Suhl peak and a few smaller, distinguishable ones on either side. The former clearly indicates that the Kondo phenomenon has its impact on A/E (non-Kondo processes), which are driven by the coupling involving the dipole moment of quantum dot transitions reflecting the physical structure of the dot including the confinement potential, in the Kondo regime.