Electron spin relaxation by nuclei and holes in single InAs quantum dots (original) (raw)
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Fast exciton spin relaxation in single quantum dots
Physical Review B, 2005
Exciton spin relaxation is investigated in single epitaxially grown semiconductor quantum dots in order to test the expected spin relaxation quenching in this system. We study the polarization anisotropy of the photoluminescence signal emitted by isolated quantum dots under steady-state or pulsed non-resonant excitation. We find that the longitudinal exciton spin relaxation time is strikingly short (≤100 ps) even at low temperature. This result breaks down the picture of a frozen exciton spin in quantum dots. PACS numbers: 78.67.Hc, 78.55.Cr, 78.66.Fd Spin memory effects in semiconductor quantum dots (QDs) attract presently much attention in the physics of nanostructures. The discrete energy spectrum of zerodimensional carriers in QDs is expected to lead to an inhibition of the main spin relaxation mechanisms which are known in bulk semiconductors and planar heterostructures [1, 2, 3]. In some novel QD devices, the preservation of the exciton spin coherence is a central issue, for instance for the generation of polarization-entangled photon-pairs in quantum information processing . Recent studies of epitaxially grown InGaAs/GaAs QDs have shown that the longitudinal exciton spin relaxation may be quenched over tens of ns at low temperature . However, it was also suggested in Ref.
Polarized fine structure in the excitation spectrum
We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wavefunctions through asymmetric e-e and e-h exchange interactions.
Luminescence and Excitation Spectra of Exciton Emission in GaAs
physica status solidi (b), 1974
Luminescence, excitation, and photoconductivity spectra of epitaxial n-and p-type BaAs at 1.6 K are measured with high resolution, using very low intensity of excitation. Under this condition, it is found that the (DO, X) bound exciton emission is split into two components, and that further structure is observable between the (D", X) and the luminescence band, recently attributed to lower branch polariton emission. In particular, two very sharp lines are seen z 0.5 meV above the (Do, X) emission. These lines are observed in all our samples, and their intensities seem to be related to the strength of the (Do, X) line. Analysis of the excitation spectra lead to the identification of three emission lines. These are the n = 2 free exciton transition, the two-electron transition of the (D O , X) complex with the donor left in the n = 3 excited state, and most probably the n = 2 donor-to-valence band transition. Mit hoher Auflosung wurden die Lumineszenzspektren, Anregungsspektren und Photoleitungsspektren von n-und p-leitendern epitaktischem GaAs bei 1,6 K gemessen. Bei Verwendung sehr geringer Anregungsintensitliten spaltet die Linie des am Donator gebundenen Exzitons (Do, X) auf und weitere Feinstruktur wird sichtbar zwischen (Do, X) und der Emissionslinie, die kurzlich dem unteren Polaritonenast zugeschrieben wurde. Insbesondere werden in allen Proben zwei sehr scharfe Linien etwa 0,5 meV oberhalb der (Do, X)-Linie beobachtet. Diese Linien scheinen in ihrer Intensitlit mit der (Do, X)-Emission korreliert zu sein. Die Analyse der Anregungsspektren erlaubt die Zuordnung dreier Emissionslinien. Dies sind der n = 2-Exzitoneniibergang, der Zwei-Elektronen-ubergang des (Do, X)-Komplexes, wobei der Donator im n = 3-Zustand verbleibt, und schlieBlich der n = 2-Donator-Valenzband-Vbergang .
Physical Review Letters, 2005
We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wavefunctions through asymmetric e-e and e-h exchange interactions.
Time-resolved spectroscopy of multiexcitonic decay in an InAs quantum dot
Physical Review B, 2002
The multi-excitonic decay process in a single InAs quantum dot is studied through high-resolution time-resolved spectroscopy. A cascaded emission sequence involving three spectral lines is seen that is described well over a wide range of pump powers by a simple model. The measured biexcitonic decay rate is about 1.5 times the single-exciton decay rate. This ratio suggests the presence of selection rules, as well as a significant effect of the Coulomb interaction on the biexcitonic wavefunction.
The Fine Structure of a Triexciton in Single InAs/GaAs Quantum Dots
Results of experimental study of multiexcitonic emission related to the p-shell of single self-assembled InAs/ GaAs quantum dots are presented. Optical properties of a rst emission line to appear from the p-shell of a strongly excited quantum dots are investigated using low-temperature polarization-sensitive micro-photoluminescence measurements. The emission line is attributed to the recombination of a complex of three electrons and holes conned in a dot (neutral triexciton), 3X. It is found that the emission consists of two linearly polarized components and the ne structure splitting is larger than the respective splitting of a neutral exciton. The optical anisotropy of the 3X emission is related to the anisotropy of the quantum dot localizing potential. The axis of the 3X optical anisotropy changes from dot to dot covering broad range within ±50 degrees with respect to the axis dened by the optical anisotropy of a neutral exciton (X). Possible origin of the deviation is discussed.
Hyperfine interaction mediated exciton spin relaxation in (In,Ga)As quantum dots
Physical Review B, 2012
The population dynamics of bright and dark excitons confined in (In,Ga)As/GaAs quantum dots have been studied as function of magnetic field by two-color pump-probe spectroscopy at cryogenic temperatures. The dark excitons are stable on a few nanoseconds time scale unless the magnetic field induces a resonance with a bright exciton state. At these resonances quasi-elastic spin flips of either electron or hole occur which are initiated by hyperfine interaction with the lattice nuclei. From the relative strength of these resonances the hole-nuclei interaction is estimated to be six times weaker than the one of the electron.
Fine Structure of Highly Charged Excitons in Semiconductor Quantum Dots
Physical Review Letters, 2003
An exciton in a symmetric semiconductor quantum dot has two possible states, one dark and one bright, split in energy by the electron-hole exchange interaction. We demonstrate that for a doubly charged exciton, there are also two states split by the electron-hole exchange, but both states are now bright. We also uncover a fine structure in the emission from the triply charged exciton. By measuring these splittings, and also those from the singly charged and doubly charged biexcitons, all on the same quantum dot, we show how the various electron-hole exchange energies can be measured without having to break the symmetry of the dot.