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On-demand confinement of semiconductor excitons by all-optical control  [PDF]
M. Alloing,A. Lemaitre,E. Galopin,F. Dubin
Physics , 2012,
Abstract: In condensed-matter physics, remarkable advances have been made with atomic systems by establishing a thorough control over cooling and trapping techniques. In semiconductors, this method may also provide a deterministic approach to reach the long standing goal of harnessing collective quantum phenomena with exciton gases. While long-lived excitons are simply cooled to very low temperatures using cryogenic apparatus, engineering confining potentials has been a challenging task. This degree of control was only achieved recently with devices realized by highly demanding nano-fabrication processes. Here, we demonstrate an alternative to this technology and show how a proper optical excitation allows to manipulate in-situ the exciton transport. Our approach is based on the optically controlled injection and spatial patterning of charges trapped in a field-effect device. Thus, electric field gradients are created and implement microscopic traps or anti-traps for the excitons dipole. Accordingly, any confinement geometry can be realized by shaping the spatial profile of a laser excitation. Hence, we succeed in trapping exciton gases in a density range where quantum correlations are predicted at our very low bath temperature.
Polarization dynamics in quantum dots: The role of dark excitons  [PDF]
E. Tsitsishvili,H. Kalt
Physics , 2014,
Abstract: We study an impact of the fine structure of the heavy--hole ground state exciton confined in semiconductor quantum dots on the photoluminescence polarization dynamics solving the relevant system of the rate equations. The presence of the dark excitons is usually ignored and the polarization decay is assumed to be caused by direct transitions within the radiative doublet. We demonstrate that in strongly confined quantum dots the dark excitons, which are energetically well below the bright excitons, have actually a decisive effect on the polarization dynamics due to their persistent nature. The linear polarization shows nonexponential decay controlled by a conversion of the dark into a bright exciton. To get quantitative answers for specific quantum dot structures, all the necessary information can be obtained already from experiments on the luminescence dynamics following nonresonant excitation in these dots.
Correlation versus mean-field contributions to excitons, multi-excitons, and charging energies in semiconductor quantum dots  [PDF]
J. Shumway,A. Franceschetti,Alex Zunger
Physics , 2000, DOI: 10.1103/PhysRevB.63.155316
Abstract: Single-dot spectroscopy is now able to resolve the energies of excitons, multi-excitons, and charging of semiconductor quantum dots with ~<1 meV resolution. We discuss the physical content of these energies and show how they can be calculated via Quantum Monte Carlo (QMC) and Configuration Interaction (CI) methods.
Theory of excitons in cubic III-V semiconductor GaAs, InAs and GaN quantum dots: fine structure and spin relaxation  [PDF]
H. Tong,M. W. Wu
Physics , 2011, DOI: 10.1103/PhysRevB.83.235323
Abstract: Exciton fine structures in cubic III-V semiconductor GaAs, InAs and GaN quantum dots are investigated systematically and the exciton spin relaxation in GaN quantum dots is calculated by first setting up the effective exciton Hamiltonian. The electron-hole exchange interaction Hamiltonian, which consists of the long- and short-range parts, is derived within the effective-mass approximation by taking into account the conduction, heavy- and light-hole bands, and especially the split-off band. The scheme applied in this work allows the description of excitons in both the strong and weak confinement regimes. The importance of treating the direct electron-hole Coulomb interaction unperturbatively is demonstrated. We show in our calculation that the light-hole and split-off bands are negligible when considering the exciton fine structure, even for GaN quantum dots, and the short-range exchange interaction is irrelevant when considering the optically active doublet splitting. We point out that the long-range exchange interaction, which is neglected in many previous works, contributes to the energy splitting between the bright and dark states, together with the short-range exchange interaction. Strong dependence of the optically active doublet splitting on the anisotropy of dot shape is reported. Large doublet splittings up to 600 $\mu$eV, and even up to several meV for small dot size with large anisotropy, is shown in GaN quantum dots. The spin relaxation between the lowest two optically active exciton states in GaN quantum dots is calculated, showing a strong dependence on the dot anisotropy. Long exciton spin relaxation time is reported in GaN quantum dots. These findings are in good agreement with the experimental results.
Coulomb correlations evidenced in the magneto-optical spectra of charged excitons in semiconductor quantum dots  [PDF]
D. Y. Oberli,M. Byszewski,B. Chalupar,E. Pelucchi,A. Rudra,E. Kapon
Physics , 2008,
Abstract: The emission spectral pattern of a charged exciton in a semiconductor quantum dot is composed of a quadruplet of linearly polarized lines in the presence of a magnetic field oriented perpendicularly to the direction of the photon momentum. By measuring the Zeeman splittings, we obtain the effective g factors of the carriers and find that the hole g factor is very sensitive to the QD shape asymmetry. By comparing the effective g factors obtained for the neutral and the charged excitons in the same quantum dot, we uncover the role of Coulomb correlations in these excitonic states.
Phonon-assisted transitions from quantum dot excitons to cavity photons  [PDF]
Ulrich Hohenester,Arne Laucht,Michael Kaniber,Norman Hauke,Abbas Mohtashami,Marek Seliger,Jonathan J. Finley
Physics , 2009, DOI: 10.1103/PhysRevB.80.201311
Abstract: For a single semiconductor quantum dot embedded in a microcavity, we theoretically and experimentally investigate phonon-assisted transitions between excitons and the cavity mode. Within the framework of the independent boson model we find that such transitions can be very efficient, even for relatively large exciton-cavity detunings of several millielectron volts. Furthermore, we predict a strong detuning asymmetry for the exciton lifetime that vanishes for elevated lattice temperature. Our findings are corroborated by experiment, which turns out to be in good quantitative and qualitative agreement with theory.
Nonlinear Rabi Oscillations of Excitons in Dense Quantum Dot System  [PDF]
Y. Mitsumori,A. Hasegawa,M. Sasaki,H. Maruki,F. Minami
Physics , 2003,
Abstract: Nonlinear optical response and optical coherence of excitons in semiconductor dense quantum dots in GaAs single quantum wells has been studied by using photon echo techniques. At low temperatures, the optical coherence is estimated to be 2 ns from the decay curve in the photon echo signal. Rabi oscillations are also observed. Unlike the results for a single quantum dot in the literature to date, the oscillation shows nonlinear behavior affected strongly by the pre-excited carrier density. The results can be explained by the theory of the local field correction originating from exciton-exciton interaction between the inter dots.

Liu Shi-an,Lin Shi-ming,Wang Qi-ming,

中国物理 B , 1999,
Abstract: In this paper, we introduced the dressed exciton model of the semiconductor micro-cavity device. In the semiconductor micro cavity of vertical-cavity surface-emission device, the excitons first coupled with the cavity through an intra-electromagnetic field and formed the dressed excitons. Then these dressed excitons decayed into the vacuum cavity optical mode, as a multi-particle process. Through the quantum electrodynamics method, the dipole emission density and system energy decayed equation were obtained. And it was predicted that the excitons decay into a very narrow mode when the exciton-cavity coupling becomes strong enough.
Theory of Coherent Optical Control of Exciton Spin Dynamics in a Semiconductor Quantum Dot  [PDF]
Pochung Chen,C. Piermarocchi,L. J. Sham
Physics , 2000, DOI: 10.1016/S1386-9477(01)00043-1
Abstract: We use the spin-polarized excitons in a single quantum dot to design optical controls for basic operations in quantum computing. We examine the ultrafast nonlinear optical processes required and use the coherent nonlinear optical responses to deduce if such processes are physically reasonable. The importance and construction of an entangled state of polarized exciton states in a single quantum dot is explained. We put our proposal in perspective with respect to a number of theoretical suggestions of utilizing the semiconductor quantum dots.
Excitons and charged excitons in semiconductor quantum wells  [PDF]
C. Riva,F. M. Peeters,K. Varga
Physics , 2000, DOI: 10.1103/PhysRevB.61.13873
Abstract: 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.
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