Far-infrared response of quantum dots: From few electron excitations to magnetoplasmons

We study the far-infrared (FIR) response of quantum dots with a variable number N_s of electrons and a non-parabolic confinement in a magnetic field B. For few electrons we compare the results of a Hartree (H) and a Hartree-Fock (HF) approach with those obtained by an exact diagonalization of the few-particle Hamiltonian. A good qualitative agreement is found between the HF approximation and the exact calculation. The resonance spectra are fingerprints of the ground state of the electron system and depend therefore strongly on N_s and B. With an increasing number of electrons, the H- and the HF-calculations show new features evolving in the FIR spectra. These features resemble the non-local mode coupling effects observed in the magnetoplasmon dispersion of two- and one-dimensional systems marking the transition to a quasi-classical hydrodynamic behaviour.