Collective Properties of Electrons and Holes in Coupled Quantum Dots (original) (raw)

Electron-hole localization in coupled quantum dots

Physical Review B, 2002

We theoretically investigate correlated electron-hole states in vertically coupled quantum dots. Employing a prototypical double-dot confinement and a configuration-interaction description for the electron-hole states, it is shown that the few-particle ground state undergoes transitions between different quantum states as a function of the interdot distance, resulting in unexpected spatial correlations among carriers and in electron-hole localization. Such transitions provide a direct manifestations of inter-and intradot correlations, which can be directly monitored in experiments.

Theory of electron-hole exchange interaction in double quantum dots

Physica Status Solidi B, 2009

A theory of electron–hole exchange interaction in vertically stacked double quantum dots is developed. This theory was built up from the full interacting Hamiltonian of two coupled dots, taking into account both of the macroscopic and microscopic natures of particle wave functions. In the basis of S-type Fock–Darwin orbitals, compact formulations for electron–hole exchange terms responsible for the fine structure splitting of spin exciton states as functions of material parameters, geometric structure of dots, and the strength of external field are explicitly derived. Significant reduction of the splitting, down to 50% of the magnitude of such energy in single dot cases, is observed as the system is switched into the near-resonance regime.

Electron-hole correlations in semiconductor quantum dots with tight-binding wave functions

Physical Review B, 2001

The electron-hole states of semiconductor quantum dots are investigated within the framework of empirical tight-binding descriptions for Si, as an example of an indirect gap material, and InAs and CdSe as examples of typical III-V and II-VI direct-gap materials. The electron-hole Coulomb interaction is largely insensitive to both the real-space description of the atomic basis orbitals and different ways of optimizing the tight-binding parameters. Tight-binding parameters that are optimized to give the best effective masses significantly improve the energies of the excitonic states due to the better single-particle energies. However, the Coulomb interaction does not vary much between different parameterizations. In addition, the sensitivity of the Coulomb interaction to the choice of atomic orbitals decreases with increasing dot size. Quantitatively, tight-binding treatments of correlation effects are reliable for dots with radii larger than 15-20Å. The calculated excitonic gaps are in good agreement with recent photoluminescence data for Si and CdSe but agree less well for InAs. Further, the effective range of the electron-hole exchange interaction is investigated in detail. In quantum dots of the direct-gap materials InAs and CdSe, the exchange interaction can be long-ranged, extending over the whole dot when there is no local (onsite) orthogonality between the electron and hole wave functions. By contrast, for Si quantum dots the extra phase factor due to the indirect gap effectively limits the range to about 15Å, independent of the dot size.

Coupling and Entangling of Quantum States in Quantum Dot Molecules

Science, 2001

We demonstrate coupling and entangling of quantum states in a pair of vertically aligned, self-assembled quantum dots by studying the emission of an interacting electron-hole pair (exciton) in a single dot molecule as a function of the separation between the dots. An interaction-induced energy splitting of the exciton is observed that exceeds 30 millielectron volts for a dot layer separation of 4 nanometers. The results are interpreted by mapping the tunneling of a particle in a double dot to the problem of a single spin. The electron-hole complex is shown to be equivalent to entangled states of two interacting spins.

Theory of spin states in coupled quantum dots

physica status solidi (b), 2006

The coherent quantum coupling of carriers in vertically stacked asymmetric pairs of quantum dots in applied electric fields manifests itself in rich photoluminescence spectral patterns of level crossings and anticrossings. These patterns arise from configurations of charges and spins in optically excited coupled quantum dots. We present a theoretical model that provides a useful picture of these optical properties including spin structure in terms of a minimal number of physical parameters.

Excitonic clusters in coupled quantum dots

Journal of Physics A: Mathematical and General, 2003

We present a first-principles path integral Monte Carlo study of a finite number of strongly correlated electron-hole pairs in two symmetric vertically coupled quantum dots. In this system, the intra-and interdot correlations depend on the distance d between the dots, the density n (strength of confinement potential) and temperature T. For fixed d and T > 0, increasing n leads to four qualitatively different states: an exciton 'liquid', an exciton 'crystal', orientationally decoupled electron and hole 'crystals' and an electron (hole) liquid.

Electronic states and tunneling times in coupled self-assembled quantum dots

Superlattices and Microstructures, 2001

Electron energy levels in single dots, and energy splitting and tunneling times in stacked quantum dots are calculated as functions of structure parameters. An effective mass approach is used to solve the Schrödinger equation for cylindrical dots with finite confinement potentials. Strong confinement due to small sizes produces quantized energy levels in single dots and strong interactions of the wavefunctions with adjacent dots. This electronic coupling induces significant energy splittings and short tunneling times for characteristic structures used in experiments. This coupling may even yield coherent artificial molecular states with different optical properties.

Electronic Properties and Spin Polarization in Coupled Quantum Dots

2021

Electronic structure and charging properties of an electrostatically defined double quantum dot system are investigated within the local spin density approximation under the density functional theory. Characteristics of electron charging of the double dot system is influenced by quantum-mechanical as well as electrostatic coupling between the individual dots. In the case of weak coupling, the double dot system is shown to exhibit double electron charging in agreement with the observations of Waugh et al. ͓Phys. Rev. Lett. 75, 705 ͑1995͔͒. Also, the coupled dot system shows spin polarization for higher number of electrons in the dot N due to Hund's rule. For strong coupling, we show that coherent bonding and antibonding states are formed which produce a reordering of the single-particle energy levels and revert the double dot system into a spin unpolarized state for same N. ͓S0163-1829͑99͒05435-1͔

Entangled states of electron–hole complex in a single InAs/GaAs coupled quantum dot molecule

Physica E: Low-dimensional Systems and Nanostructures, 2002

We summarize here results of calculations and experiments on electron and valence hole states in a single pair of vertically stacked and electronically coupled InAs self-assembled quantum dots. In perfectly aligned quantum dots one can relate an electron-hole complex to a pair of entangled qubits. The information carried by individual qubit is related to the quantum dot index (isospin) of individual carrier. The quality of fabricated quantum dot molecules is identiÿed from the exciton ÿne structure in a magnetic ÿeld. ?