Vertically coupled double quantum rings at zero magnetic field

Within local-spin-density functional theory, we have investigated the `dissociation' of few-electron circular vertical semiconductor double quantum ring artificial molecules at zero magnetic field as a function of inter-ring distance. In a first step, the molecules are constituted by two identical quantum rings. When the rings are quantum mechanically strongly coupled, the electronic states are substantially delocalized, and the addition energy spectra of the artificial molecule resemble those of a single quantum ring in the few-electron limit. When the rings are quantum mechanically weakly coupled, the electronic states in the molecule are substantially localized in one ring or the other, although the rings can be electrostatically coupled. The effect of a slight mismatch introduced in the molecules from nominally identical quantum wells, or from changes in the inner radius of the constituent rings, induces localization by offsetting the energy levels in the quantum rings. This plays a crucial role in the appearance of the addition spectra as a function of coupling strength particularly in the weak coupling limit.Comment: 18 pages, 8 figures, submitted to Physical Review

Excitons and charged excitons in semiconductor quantum wells

A variational calculation of the ground-state energy of neutral excitons and of positively and negatively charged excitons (trions) confined in a single-quantum well is presented. We study the dependence of the correlation energy and of the binding energy on the well width and on the hole mass. The conditional probability distribution for positively and negatively charged excitons is obtained, providing information on the correlation and the charge distribution in the system. A comparison is made with available experimental data on trion binding energies in GaAs-, ZnSe-, and CdTe-based quantum well structures, which indicates that trions become localized with decreasing quantum well width.Comment: 9 pages, 11 figure

Renormalization approach for quantum-dot structures under strong alternating fields

We develop a renormalization method for calculating the electronic structure of single and double quantum dots under intense ac fields. The nanostructures are emulated by lattice models with a clear continuum limit of the effective-mass and single-particle approximations. The coupling to the ac field is treated non-perturbatively by means of the Floquet Hamiltonian. The renormalization approach allows the study of dressed states of the nanoscopic system with realistic geometries as well arbitrary strong ac fields. We give examples of a single quantum dot, emphasizing the analysis of the effective-mass limit for lattice models, and double-dot structures, where we discuss the limit of the well used two-level approximation.Comment: 6 pages, 7 figure

Dissociation of vertical semiconductor diatomic artificial molecules

We investigate the dissociation of few-electron circular vertical semiconductor double quantum dot artificial molecules at 0 T as a function of interdot distance. Slight mismatch introduced in the fabrication of the artificial molecules from nominally identical constituent quantum wells induces localization by offsetting the energy levels in the quantum dots by up to 2 meV, and this plays a crucial role in the appearance of the addition energy spectra as a function of coupling strength particularly in the weak coupling limit.Comment: Accepted for publication in Phys. Rev. Let

A vertical diatomic artificial molecule in the intermediate coupling regime in a parallel and perpendicular magnetic field

We present experimental results for the ground state electrochemical potentials of a few electron semiconductor artificial molecule made by vertically coupling two quantum dots, in the intermediate coupling regime, in perpendicular and parallel magnetic fields up to 5 T. We perform a quantitative analysis based on local-spin density functional theory. The agreement between theoretical and experimental results is good, and the phase transitions are well reproduced.Comment: Typeset using Revtex, 13 pages and 8 Postscript figure

On the observability of the acoustic plasma mode in double-layered quantum dots

Double-layered quantum dots represent a novel realization of a multi-component plasma system. By modelling the system and applying classical concepts we investigate the oscillator strength of the acoustic plasma mode and its dependence on the system parameters. In view of recent experimental results, we discuss the observability of this collective excitation

Double-layered quantum dots in a magnetic field: The ground state and the far-infrared response

We investigate the ground-state properties, the far-infrared (FIR) response, and the collective modes of a square lattice of double-layered quantum dots by applying classical and quantum-mechanical concepts. Using classical self-consistent linear response theory for the dot array we derive analytic results for the magnetoabsorption spectrum and the frequencies, linewidths, and oscillator strengths of the optical and acoustic collective modes including the effect of intercell and intracell interactions. Within the full quantum-mechanical calculation (applying density-functional theory with the local-density approximation) for a single double-layered quantum dot we obtain numerically ground-state properties and the FIR excitation frequencies. We use a quantum dot model with a realistic distribution of background charge, which accounts for surface states and total charge neutrality. In both approaches we study the dependence of the oscillator strengths of the acoustic mode on the asymmetry of the double-layered system in order to give information on the condition for experimental detection

Integer filling facfor phases and isospin in vertical diatomic artificial molecules

Integer filling factor phases of many-electron vertically coupled diatomic artificial quantum dot molecules are investigated for different values of the interdot coupling. The experimental results are analyzed within local-spin density functional theory for which we have determined a simple lateral confining potential law that can be scaled for the different coupling regimes, and Hartree-Fock theory. Maximum density droplets composed of electrons in both bonding and antibonding or just bonding states are revealed, and interesting isospin-flip physics appears for weak interdot coupling when the systematic depopulation of antibonding states leads to changes in isospin