Experimental imaging and atomistic modeling of electron and hole quasiparticle wave functions in InAs/GaAs quantum dots

We present experimental magnetotunneling results and atomistic pseudopotential calculations of quasiparticle electron and hole wave functions of self-assembled InAs/GaAs quantum dots. The combination of a predictive theory along with the experimental results allows us to gain direct insight into the quantum states. We monitor the effects of (i) correlations, (ii) atomistic symmetry and (iii) piezoelectricity on the confined carriers and (iv) observe a peculiar charging sequence of holes that violates the Aufbau principle.Comment: Submitted to Physical Review B. A version of this paper with figures can be found at http://www.sst.nrel.gov/nano_pub/mts_preprint.pd

Recent advances in exciton based quantum information processing in quantum dot nanostructures

Recent experimental developments in the field of semiconductor quantum dot spectroscopy will be discussed. First we report about single quantum dot exciton two-level systems and their coherent properties in terms of single qubit manipulations. In the second part we report on coherent quantum coupling in a prototype "two-qubit" system consisting of a vertically stacked pair of quantum dots. The interaction can be tuned in such quantum dot molecule devices using an applied voltage as external parameter.Comment: 37 pages, 15 figures, submitted to New Journal of Physics, focus issue on Solid State Quantum Information, added reference

Fine structure of negatively and positively charged excitons in semiconductor Quantum dots:Electron-hole asymmetry

We present new understanding of excitonic fine structure in close-to-symmetric InAs / GaAs and InGaAs / GaAs quantum dots. We demonstrate excellent agreement between spectroscopy and many-body pseudopotential theory in the energy splittings, selection rules and polarizations of the optical emissions from doubly charged excitons. We discover a marked difference between the fine structure of the doubly negatively and doubly positively charged excitons. The features in the doubly charged emission spectra are shown to arise mainly from the lack of inversion symmetry in the underlying crystal lattice

Structure of quantum dots as seen by excitonic spectroscopy versus structural characterization: Using theory to close the loop

Structure-spectra relationship in semiconductor quantum dots (QDs) is investigated by subjecting the same QD sample to single-dot spectroscopy and cross-sectional scanning tunneling microscopy (XSTM) structural measurements. We find that the conventional approach of using XSTM structure as input to calculate the spectra produces some notable conflicts with the measured spectra. We demonstrate a theoretical inverse approach which deciphers structural information from the measured spectra and finds structural models that agree with both XSTM and spectroscopy data. This effectively closes the loop between structure and spectroscopy in QDs

Predicting the electronic properties of 3D, million-atom semiconductor nanostructure architectures

corresponding author’

Peculiar many-body effects revealed inthespectroscopy of highly charged quantumdots

Coulomb interactions between electrons lead to the observed multiplet structure and breakdown of the Aufbau principle for atomic d and f shells1. Nevertheless, these effects can disappear in extended systems. For instance, the multiplet structure of atomic carbon is not a feature of graphite or diamond. A quantum dot is an extended system containing ∼106 atoms for which electron–electron interactions do survive and the interplay between the Coulomb energy, J, and the quantization energy, ΔE, is crucial to Coulomb blockade2,3,4,5. We have discovered consequences of Coulomb interactions in self-assembled quantum dots by interpreting experimental spectra with an atomistic calculation. The Coulomb effects, evident in the photon emission process, are tunable in situ by controlling the quantum dot charge from +6e to −6e. The same dot shows two regimes: J≤ΔE for electron charging yet J≃ΔE for hole charging. We find a breakdown of the Aufbau principle for holes; clear proof of non-perturbative hole–hole interactions; promotion–demotion processes in the final state of the emission process, effects first predicted a decade ago6; and pronounced configuration hybridizations in the initial state. The level of charge control and the energy scales result in Coulomb effects with no obvious analogues in atomic physics