Hyperfine interaction mediated exciton spin relaxation in (In,Ga)As quantum dots

The population dynamics of dark and bright excitons in (In,Ga)As/GaAs quantum dots is studied by two-color pump-probe spectroscopy in an external magnetic field. With the field applied in Faraday geometry and at T < 20 K, the dark excitons decay on a ten nanoseconds time scale unless the magnetic...

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Bibliographic Details
Published in:Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2012-05, Vol.85 (19), Article 195303
Main Authors: Kurtze, H., Yakovlev, D. R., Reuter, D., Wieck, A. D., Bayer, M.
Format: Article
Language:English
Subjects:
Condensed matter
Excitation
Gallium arsenides
Magnetic fields
Magnetic resonance
Nanostructure
Quantum dots
Relaxation time
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Summary:The population dynamics of dark and bright excitons in (In,Ga)As/GaAs quantum dots is studied by two-color pump-probe spectroscopy in an external magnetic field. With the field applied in Faraday geometry and at T < 20 K, the dark excitons decay on a ten nanoseconds time scale unless the magnetic field induces a resonance with a bright exciton state. At these crossings their effective lifetime is drastically shortened due to spin flips of either electron or hole by which the dark excitons are converted into bright ones. Due to the quasielastic character we attribute the origin of these flips to the hyperfine interaction with the lattice nuclei. We compare the exciton spin relaxation times in the two resonances and find that the spin flip involving an electron is approximately 25 times faster than the one of the hole. A temperature increase leads to a considerable, nonmonotonic decrease of the dark exciton lifetime. Here phonon-mediated spin flips due to the spin-orbit interaction gradually become more important.
ISSN:1098-0121
1550-235X
DOI:10.1103/PhysRevB.85.195303