Hybrid molecules formed by coupling semiconductor quantum dots to metal nanoparticle nanoantennas provide a new paradigm for directed nanoscale transfer of quantum information. To assess this possibility, we study theoretically the response of these hybrid molecules to applied optical fields. Quantum-coherent time-evolution of the semiconductor quantum dots in the hybrid molecule is found by solving the semiconductor quantum dot density matrix equations. We study hybrid molecules in the weak and strong coupling regimes. In strongly driven, strongly dipole-coupled semiconductor quantum dot-metal nanoparticle hybrids with spherical metal nanoparticles, interference, dispersion near resonance and self interaction define the metal nanoparticle/semiconductor quantum dot coupling and lead to the Fano resonances, exciton induced transparency, suppressed semiconductor quantum dot response and bistability. More complicated response can be tailored by using metal nanoparticle shape and the placement of semiconductor quantum dots to control the local near-fields that couple the metal nanoparticles and semiconductor quantum dots. We describe how coupling to metal nanoparticle dark modes and higher order multipolar modes impact interference and self-interaction effects. The physics of the metal nanoparticle/semiconductor quantum dot coupling is outlined.
The empirical tight-binding approach is used to study atomic-scale effects on electronic coupling in vertically stacked, self-assembled InAs/GaAs quantum dots. A model with unstrained dots is first studied to isolate the atomistic coupling effects from the strain effects. The strain effects are next considered by means of the valence force field method. Electron levels in coupled quantum dots follow closely the simple analogy of coupled dots as artificial molecules. The electron ground state of double dot has always bonding-like character. The coupling of hole states is more complicated because the coupling depends both of the hole envelope function and the atomic character of the hole state. It is shown that the character of the hole ground state of double dot changes from antibonding to bonding-like, when the distance between the dots decreases. It reorders hole levels, changes state symmetries, and makes changes in optical spectra. The calculated red-shift of the lowest transition for closely-spaced dots agrees well with experimental data. We present also some preliminary results on strain effects in such nanocrystals.
Erratum: M. Zieliński, W. Jaskólski, J. Aizpurua, G.W. Bryant, Strain and Spin-Orbit Effects in Self-Assembled Quantum Dots, Acta Phys. Pol. A, 108, 929, 2005.
The effects of strain and spin-orbit interaction in self-assembled lens-shaped InAs/GaAs quantum dots are investigated. Calculations are performed with empirical tight-binding theory supplemented by the valence force field method to account for effects of strain caused by lattice mismatch at the InAs-GaAs interface. It is shown that both effects influence strongly the electron and hole energy structure: splitting of the energy levels, the number of bound states, density distributions, and transition rates. We show that piezoelectric effects are almost negligible in quantum dots of the size investigated.
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