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1
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On Subband Mobilities Observed in δ-doped AlGaAs/GaAs Quantum Wells and GaAs Layers

100%
Dobaczewski L., Maude D., Missous M., Portal J.
Acta Physica Polonica A
|
1995
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vol. 87
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issue 1
201-204
EN
Electronic transport phenomena in molecular beam epitaxy grown sil­icon δ-doped AlGaAs/GaAs quantum wells and GaAs layers were investi­gated. Observations of the Shubnikov-de Haas oscillations allowed to deduce the redistribution of electrons among energy subbands formed by V-shaped and rectangular wells for GaAs layers and the AlGaAs/GaAs quantum wells, respectively. In both cases the effects of illumination upon individual sub-band mobilities and carrier concentrations were studied and the manifesta­tion of the DX centres was demonstrated.
2
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Application of Generalized Pair Approximation to Diluted Magnetic Semiconductor Quantum Structures

100%
Bednarski H., Cisowski J., Portal J.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
723-726
EN
Analysing the d-d interaction in diluted magnetic semiconductor quantum structures, we used our generalized pair approximation which permits to take into account the real spatial distribution of the magnetic ions in diluted magnetic semiconductor layers close to the nonmagnetic quantum well. We subsequently applied our approach to calculate the Zeeman splittings in the CdTe/Cd_{1-x}Mn_{x}Te quantum structures with x=5 and 7.5% and we obtained a good agreement with the experimental results.
3
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Anisotropy of the Exchange Interaction in Mn-Alloyed II_{3}-V_{2} Compounds

100%
Lubczyński W., Cisowski J., Portal J.
Acta Physica Polonica A
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1991
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vol. 80
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issue 2
275-278
EN
An anisotropy of the electron effective g-factor in highly degenerated tetragonal semimagnetic semiconductors (SMSC) alloyed with manganese has been found by us and by other workers when studying the Shubnikov-de Haas (SdH) effect for different orientations of the magnetic field with respect to the crystal axes. The detailed analysis of the experimental data by using a model based on an infinite Hamiltonian matrix, provides evidence for the anisotropy of the p-d exchange interaction in the materials of interest.
4
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Influence of Pressure on Magnetization of (Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2}

88%
Bednarski H., Cisowski J., Lubczyński W., Voiron J., Portal J.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
205-208
EN
The influence of hydrostatic pressure up to 0.6 GPa on magnetization of (Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2} with various compositions was studied at 4.2 K and in magnetic fields up to 7 T. The obtained experimental data were analysed within our generalized pair approximation model, treating the total Mn-Mn interaction strength as a sum of superexchange and the Bloembergen-Rowland exchange. As a result, we obtained satisfactory agree­ment between our approach and experiment by introducing a pressure de­pendence of p-d hybridization potential V_{pd} in the form V_{pd} ∝ d^{-4}, where d is the Mn-As bond length which decreases with pressure.
5
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Magnetic Specific Heat of (Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2}

76%
Bednarski H., Cisowski J., Schmitt D., Voiron J., Portal J., Lubczyński W.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
705-708
EN
The specific heat of (Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2} with low Mn concentration (x ≤ 0.067) and for two Zn contents (y = 0.14 and y = 0.34) has been measured in the temperature range of 1.5-30 K. The magnetic contribution to the total specific heat has been analysed within our generalized pair approximation model which takes into account the complicated tetragonal crystal structure of Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2}. Assuming that the total Mn-Mn interaction strength is a sum of superexchange and the Bloembergen-Rowland exchange, we have obtained a very good agreement between our approach and experiment by using the analytical formulae with only two adjustable parameters, i.e. the first nearest-neighbour exchange constants for both mechanisms which appear to be strongly dependent on Zn content.
6
Content available remote

Pressure Investigation of Tunneling in an InAlAs-InGaAs Double Barrier Structure

64%
Cury L., Dmowski L., Celeste A., Portal J., Davies M., Heath M., Sivco D., Cho A.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
199-202
EN
AnIn_{0.52}Al_{0.48}As-In_{0.53}Ga_{0.47}As double-barrier structure was studied under hydrostatic pressures up to 15 kbar. Two resonances in the I(V) curves are observed. The possible tunneling mechanisms to interpret this effect are analysed.
7
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Content available

Breakdown of the Quantum Hall Effect

64%
Maude D., Rigal L., Desrat W., Potemski M., Portal J., Eaves L., Wasilewski Z., Toropov A., Hill G.
Acta Physica Polonica A
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2001
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vol. 100
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issue 2
213-226
EN
The breakdown of the dissipationless conductance in the integer and fractional quantum Hall effect regime is reviewed. The temperature dependence of the critical current and of the critical magnetic field at breakdown bears a striking resemblance to the phase diagram of the phenomenological two-fluid Gorter-Casimir model for superconductivity. In addition, a remarkably simple scaling law exists between different filling factors.
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