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Femtosecond Dynamics of Neutral and Charged Exciton Absorption in Cd_{1-x}Mn_xTe Quantum Well

100%
Płochocka P., Kossacki P., Maślana W., Radzewicz C., Gaj J., Cibert J., Tatarenko S.
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issue 4-5
679-686
EN
We present a study of time-dependent transmission spectra of a modulation-doped Cd_{1-x}Mn_xTe/Cd_{1-y-z}Zn_yMg_zTe quantum well with variable hole gas concentration. We study the influence of pump pulses on excitonic absorption in subpicosecond time scale. A spectrally broad probe pulse of duration of 40 femtoseconds was used to record the absorption spectra at controlled delay. Studies of temporal evolution of exciton energies revealed coherence decay of linearly polarized excitons and thermalization of non-equilibrium exciton states. We found that a characteristic timescale for thermalization of non-equilibrium populations of photocreated excitons is between 0.8 and 3.6 ps. The timescale of this process depends on the hole concentration in quantum well: for higher hole concentration the decay is faster. Long-lived photo-induced magnetization accompanied by heating of the magnetic system was also observed.
2
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Combined Exciton-Cyclotron Resonance in Photoluminescence of a Two-Dimensional Hole Gas

100%
Jadczak J., Bryja L., Płochocka P., Wójs A., Misiewicz J., Maude D., Potemski M.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
852-853
EN
A two-dimensional hole gas in an asymmetric GaAs/Ga_{1-x}Al_{x}As quantum well is studied by polarization-resolved photoluminescence in high magnetic fields (up to B = 20 T) and at low temperatures (down to T = 50 mK). In addition to the previously reported dominant emission channels of various free and acceptor-bound trions, the high-energy hole cyclotron replicas of the bound states are now also observed, corresponding to the combined exciton-cyclotron resonance. Identification of different transitions in the rich, multi-peak spectra was possible by the analysis of optical selection rules and comparison of the experimental spectra with realistic numerical calculations.
3
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Evidence of Singlet-Triplet Crossing in Photoluminescence of Positively Charged Excitons in GaAs Quantum Wells

84%
Bryja L., Wójs A., Jadczak J., Misiewicz J., Płochocka P., Potemski M., Reuter D., Wieck A.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1073-1077
EN
Positively charged excitons in a two-dimensional hole gas in symmetric and asymmetric GaAs/Ga_{1-x}Al_{x}As quantum wells are studied in polarization-resolved photoluminescence experiments in high magnetic fields B (up to 23 T) and low temperatures (down to 300 mK). The experiments are accompanied by numerical calculations of a real structure. The whole family of trions (the singlet and a pair of triplets) are observed. The Coulomb energies crossing of singlet and triplet is found: hidden in symmetric and visible in asymmetric structures.
4
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Many-Body Interactions in the CdTe-Based Quantum Well under Strong Optical Excitation

84%
Płochocka P., Kossacki P., Piechal B., Maślana W., Golnik A., Cibert J., Tatarenko S., Gaj J.
Acta Physica Polonica A
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2004
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vol. 106
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issue 3
413-422
EN
We performed pump-probe time-resolved absorption measurements on a modulation p-doped (Cd,Mn)Te quantum well. The density of the 2D hole gas was controlled, in the 10^{10} cm^{-2} range, by additional cw illumination. Interactions between photocreated neutral (X) and charged (X^{+}) excitons and the 2D hole gas were analyzed. We found that the strongest effect is the influence of the carriers on both X and X^+ optical resonances. Neutral and charged excitons are screened by holes, which results in the decrease in their intensities. We conclude from polarization resolved experiments that this screening is spin-dependent: it is more efficient between holes with opposite spins. Binding holes into the charged excitons reduces the screening of the neutral excitons and leads to an enhancement of the neutral exciton intensity. We also analyzed weaker effects, due to exciton-exciton interaction, at a constant hole density. We found that the reduction of the neutral exciton intensity due to two different mechanisms (phase-space filling and biexciton formation) is almost equal. We observed a spin-dependent blue shift of the neutral exciton line in the presence of a population of neutral excitons created by the pump pulse. Due to the attractive interaction between excitons with opposite spins, the corresponding shift of the neutral exciton is smaller than that observed due to the interaction between excitons with the same spins.
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