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  1. 30 Acta Physica Polonica A

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  1. 30 Potemski M.

  2. 9 Wysmołek A.

  3. 8 Babiński A.

  4. 7 Bryja L.

  5. 7 Molas M.

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1
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Intershell Exchange Interaction in Charged GaAlAs Quantum Dots

100%
Molas M., Nicolet A., Potemski M., Babiński A.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
785-787
EN
Optical anisotropy of charged excitons and biexcitons related to the single-particle s- and p-shell emission in GaAlAs/AlAs quantum dots is investigated. The polarization-dependence and time-resolved micro-photoluminescence measurements were performed. Cross-correlation measurements were used to identify the ladder of excitonic states and allowed us to show two cascade pathways, including the spin singlet and triplet states of charged excitons and biexcitons. The fine structure of the studied states is described and analysed in terms of electron-electron, hole-hole, and electron-hole exchange interactions.
2
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Band Mixing Effects in Quantum Well Magnetoexcitons

100%
Wysocki R., Bardyszewski W., Schoser S., Potemski M.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
1067-1071
EN
The influence of intersubband mixing in quantum wells of semiconductors with zinc-blende structure is studied both experimentally and theoretically. A multiband magnetoexciton model is described which takes into account k∙p mixing between valence subbands and the effective Coulomb interaction for an arbitrary confinement potential shape. Theoretical results reproduce very well the photoluminescence excitation spectra of GaAs/AlGaAs single quantum wells of various widths. In particular, the characteristic avoided crossing between the lowest light-hole exciton Landau level and excited heavy-hole exciton Landau level occurring at σ¯ polarization is accurately described by our theory.
3
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Magnetic Field Effect on the Excitation Spectrum of a Neutral Exciton in a Single Quantum Dot

88%
Molas M., Nicolet A., Piętka B., Babiński A., Potemski M.
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vol. 126
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issue 5
1066-1068
EN
Excitation-energy-dependent magnetospectroscopic measurements of a single GaAlAs/AlAs quantum dot were performed. A significant effect of the excitation energy on the photoluminescence spectra is reported. The photoluminescence excitation spectroscopy has been used to investigate the excitation spectrum of a single electron-hole pair - a neutral exciton in magnetic field up to 14 T. The observed resonances exhibit diamagnetic shift characteristic of an s-shell related emission. In our opinion, the creation of excited complexes involving an excited hole and a ground electron is responsible for the process.
4
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Skyrmions in a Hole Gas with Large Spin Gap and Strong Disorder

88%
Bryja L., Ryczko K., Wójs A., Misiewicz J., Potemski M.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
163-168
EN
In the photoluminescence excitation spectra of two-dimensional valence holes with large spin gap and strong disorder we find evidence for quantum Hall ferromagnetism and small skyrmions around the Landau level filling factorν=1. This interpretation is supported by numerical calculations.
5
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Fine Structure of Neutral Excitons in Single GaAlAs Quantum Dots

88%
Molas M., Gołasa K., Piętka B., Potemski M., Babiński A.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
988-990
EN
Optical anisotropy of neutral excitons in GaAlAs/AlAs quantum dots is investigated. Low-temperature polarization-sensitive photoluminescence measurements of single quantum dots are performed. It is found that neutral excitons (X) in the quantum dots exhibit a fine structure splitting. The fine structure splitting ranges from 10 μeV to 100 μeV and correlates with the X energy. The polarization axis of the fine structure splitting is well oriented along [110] crystallographic direction of a substrate. The orientation is attributed to the elongation of GaAlAs/AlAs quantum dots in the [110] direction of the substrate.
6
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Magnetoresistance and Electroluminescence near the Curie-Weiss Temperature in the Zn_{1-x}Mn_{x}Te Light Emitting Devices

88%
Van Khoi L., Avdonin A., Szymczak R., Gałązka R., Potemski M.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
941-943
EN
The light emitting devices based on the p-Zn_{1-x}Mn_{x}Te bicrystals have been fabricated. The Zn_{1-x}Mn_{x}Te devices produce red and green emission originating from the internal d-shell transitions in the Mn^{2+} ions and the donor-acceptor pairs recombination, respectively. A critical behavior of the magnetic field dependence of the green emission intensity and a positive magnetoresistance near the Curie-Weiss temperature in the Zn_{1-x}Mn_{x}Te devices was observed.
7
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Ferromagnetic, Ferrimagnetic and Spin-wave Resonances in GaMnAs Layers

88%
Fedorych O., Byszewski M., Wilamowski Z., Potemski M., Sadowski J.
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issue 4-5
617-625
EN
Molecular beam epitaxy grown Ga_{1-x}Mn_xAs layers were investigated by means of magnetic resonances. With an increase in Mn concentration, x, the spectrum changes from the (i) paramagnetic one, with resolved fine and hyperfine structures, typical of S=5/2 spin of substitutional Mn^{2+} ions, for very diluted alloy, via (ii) paramagnetic spectrum, where the fine and hyperfine structures are averaged by a long range Mn^{2+}-Mn^{2+} exchange coupling, (iii) single, isotropic line of ferromagnetic resonance. Insulator to metal transition is accompanied with occurrence of (iv) a very complex spectrum of the ferrimagnetic resonance, accompanied with the well-resolved spin wave resonance. Reentrance to insulator phase for the most condensed alloys is accompanied with the reentrance to (v) ferromagnetic phase. The data confirm that the effective mass holes transfer the exchange interaction between localized Mn^{2+} spins.
8
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Time Resolved Magnetophotoluminescence of Biased GaAs/AlGaAs Double Quantum Well Structure

88%
Surowiecka K., Wysmołek A., Stępniewski R., Potemski M., Henini M.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1369-1374
EN
Time resolved photoluminescence of double quantum well structure was investigated versus electric and magnetic fields applied across the sample. The emission due to direct excitons (electron and hole are localized within the same quantum well) decays fast at the nanosecond timescale, whereas the recombination kinetics of indirect excitons is much slower and spreads over microseconds. The time evolution of indirect exciton emission is shown to be altered by application of either electric or magnetic field. This reflects the non-trivial effects of exciton localization which leads to the non-exponential decays of the indirect exciton emission.
9
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Magnetic Resonance Studies of the Origin of Ferromagnetism in Ga_{1-x}Mn_xAs

88%
Fedorych O., Wilamowski Z., Potemski M., Byszewski M., Sadowski J.
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EN
Different types of magnetic resonance observed in Ga_{1-x}Mn_xAs reflect three different magnetic phases: para-, ferro-, and ferrimagnetic. Ferromagnet is characterized by single isotropic resonance line. A complex spectrum in ferrimagnet can be described by g factor equal to 1.44 and a sum of an axial and cubic anisotropy field. The axial field is by an order of magnitude greater than the cubic one. The complex structure of ferrimagnetic resonance is attributed to spin-wave resonance. Quantitative analysis of the dispersion of spin wave shows that the range of exchange coupling is very long, of the order of 25 nm, while spin-wave stiffness and the total exchange field are very small. The exchange field as evaluated from spin wave is by two orders of magnitude smaller than the Zener field corresponding to the critical temperature.
10
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Shake-Up Processes in Photoluminescence of Two-Dimensional Holes in a High Magnetic Field

76%
Wójs A., Bryja L., Misiewicz J., Potemski M., Reuter D., Wieck A.
Acta Physica Polonica A
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2006
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vol. 110
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issue 3
429-435
EN
Recombination of excitons and positive trions is studied by two-beam photoluminescence of a two-dimensional hole gas in a high magnetic field. The singlet, dark-triplet and bright-triplet states of a free trion are resolved, and their binding energies are determined. Recombination of acceptor-bound trions is also detected, including a low-energy cyclotron replica, corresponding to a hole shake-up process. Identification of all these different transitions was possible by analysis of optical selection rules and the comparison of experimental spectra with realistic numerical calculations.
11
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Magneto-Luminescence Study of Silicon-Vacancy in 6H­Si

76%
Wysmołek A., Wardak K., Stępniewski R., Baranowski J., Potemski M., Tymicki E., Grasza K.
Acta Physica Polonica A
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2006
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vol. 110
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issue 3
437-442
EN
The magneto-spectroscopy studies of luminescence related to silicon-vacancy, in high quality 6H-SiC crystals grown by the seeded physical vapor transport method, are presented. The superior optical quality of these crystals allowed us to resolve a doublet structure of the 1.398 eV emission line (V_2 line), commonly assigned to the transitions involving two singlet states of the silicon-vacancy. Experiments performed in magnetic fields up to 20 T showed that each doublet constituent of the V_2 line splits into four components for the magnetic field parallel to the c-axis of the 6H-SiC crystals. This result could be hardly explained in terms of a singlet to singlet transition. The analysis of the angle-resolved luminescence experiments in high magnetic fields serves us to discuss the symmetry of the defect states responsible for the V_2-line in silicon carbide.
12
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Combined Exciton-Cyclotron Resonance in Photoluminescence of a Two-Dimensional Hole Gas

76%
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.
13
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Carriers Diffusion in GaAs/AlAs Type II Quantum Well

76%
Lesiak A., Chwalisz B., Wysmołek A., Potemski M., Stępniewski R., Thierry-Mieg V.
Acta Physica Polonica A
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2005
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vol. 108
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issue 5
755-760
EN
The micro-photoluminescence of GaAs/AlAs type II double quantum well structure is presented. The specific band alignment of the investigated system allows obtaining high concentration of long lived carriers. This enables us to study diffusion of carriers and/or indirect excitons. It was found that the carrier flow does not follow the classical diffusion equation and is driven by the potential modification due to the presence of photo created carriers.
14
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Electron-Electron Interaction Effects in Quantum Hall Regime of GaN/AlGaN Heterostructures

76%
Siekacz M., Dybko K., Maude D., Potemski M., Knap W., Skierbiszewski C.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
269-273
EN
We measured the activation of resistivity at quantum Hall minima in high mobility two-dimensional electron gas confined at AlGaN/GaN interface. The effective g-factor and effective mass was deduced. The electron-electron interactions modify both quantities compared to their bare band values. It is found that the influence of interactions is much more pronounced onto g-factor than effective mass. The relative spin susceptibility was also calculated and compared with available theories. The best agreement was found with the ideal two-dimensional gas model in random phase approximation.
15
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The Fine Structure of a Triexciton in Single InAs/GaAs Quantum Dots

76%
Molas M., Gołasa K., Furman M., Lapointe J., Wasilewski Z., Potemski M., Babiński A.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
991-993
EN
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 first 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 confined in a dot (neutral triexciton), 3X. It is found that the emission consists of two linearly polarized components and the fine 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 defined by the optical anisotropy of a neutral exciton (X). Possible origin of the deviation is discussed.
16
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Nonlinear Zeeman Splitting of Holes in Doped GaAs Heterostructures

76%
Kubisa M., Ryczko K., Jadczak J., Bryja L., Misiewicz J., Potemski M.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
609-611
EN
Polarization-resolved photoluminescence from two-dimensional GaAs/GaAlAs heterostructures doped with acceptors was studied in high magnetic fields. Measurements were carried out in low temperatures up to 2 K and magnetic field up to 21 T. Experiments performed in the Faraday configuration enabled to resolve hole states with different spin orientation. We observed a nonlinear behavior of valence-band g factor in strong magnetic fields. To explain obtained results, a detailed theoretical calculation was carried out based on the Luttinger model for valence-band states. We examined the spin splitting of hole levels under the influence of both external magnetic field and built-in electric field existing in doped heterostructures. Changes of hole g factor with the width of the structure and the density of two-dimensional carriers are discussed.
17
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Strong Photoluminescence Fluctuations in Laser-Thinned Few-Layer WS₂

76%
Bala Ł., Łacińska E., Nogajewski K., Molas M., Wysmołek A., Potemski M.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1176-1178
EN
We present results of μ-Raman and μ-photoluminescence study of few-layer WS₂ flakes that have been locally thinned down by a focused laser beam. The Raman spectroscopy measurements prove that the investigated flake was locally thinned down to a monolayer. Interestingly, μ-photoluminescence experiments allowed us to observe huge intensity fluctuations at the boundary of laser-thinned region. Similar effects were found at the edges of a WS₂ bilayer flake, which has not been subjected to laser-thinning. The origin of the observed time evolution of the photoluminescence response is discussed in terms of potential fluctuations resulting from light-induced changes of the charge state of defects.
18
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The Effect of Substrate on Vibrational Properties of Single-Layer MoS₂

76%
Gołasa K., Molas M., Nogajewski K., Grzeszczyk M., Zinkiewicz M., Potemski M., Babiński A.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1172-1175
EN
We report on the Raman scattering from single-layer molybdenum disulfide (MoS₂) deposited on various substrates: Si/SiO₂, hexagonal boron nitride (h-BN), sapphire, as well as suspended. Room temperature Raman scattering spectra are investigated under both resonant (632.8 nm) and non-resonant (514.5 nm) excitations. A rather weak influence of the substrate on the Raman scattering signal is observed. The most pronounced, although still small, is the effect of h-BN, which manifests itself in the change of energy positions of the E' and A'₁ Raman modes of single-layer MoS₂. We interpret this modification as originating from van der Waals interaction between the MoS₂ and h-BN layers.
19
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Time-Resolved Studies of Gallium Nitride Doped with Gadolinium

76%
Witek B., Wysmołek A., Kamińska M., Twardowski A., Potemski M., Boćkowski M., Grzegory I.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1425-1430
EN
Time-resolved photoluminescence experiments on high quality bulk GaN doped with Gd are presented. It was found that the decay time of Gd-related transitions observed for 4.2 K around 1.78 eV is of about 3 ms. Such a long decay time strongly supports the identification of this emission band as due to transitions between Gd³+(4f⁷) levels. The decay time measured for Gd-related transitions observed in the UV spectral range, close to the GaN band-gap, was found to be much faster than 1 μs. This suggests that these emission lines could hardly be correlated with internal transitions within Gd³+(4f⁷). Possible origin of the Gd-related UV luminescence is discussed.
20
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Emission from Mesoscopic-Size Islands Formed in a GaAs/AlAs Double Layer Structure

76%
Wysmołek A., Chwalisz B., Potemski M., Stępniewski R., Babiński A., Raymond S., Thierry-Mieg V.
Acta Physica Polonica A
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2004
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vol. 106
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issue 3
367-381
EN
The nature of sharp emission lines which are present in macro-luminescence experiments on a type-II GaAs/AlAs double quantum well structure is discussed. The experiments, which also include micro-lumines- cence measurements, allowed us to conclude that the sharp emission lines observed originate from lateral GaAlAs islands of a fewμm in diameter. They serve as efficient type-I recombination centers for indirect excitons and/or carriers which diffuse in the GaAs/AlAs QW structure and strongly affect the emission processes observed in macro-luminescence experiments. These traps can easily be filled with electron-hole pairs, giving rise to the formation of neutral excitons as well as more complex excitonic molecules. Magneto-luminescence spectra from single islands resemble those observed for natural quantum dots formed in narrow GaAs quantum wells.
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