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  1. 53 Acta Physica Polonica A

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  1. 5 Twardowski A.

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1
Content available remote

Submilimeter Magnetospectroscopy on ZnFeSe

100%
Krevet R., Kempf P., Von Ortenberg M., Twardowski A.
Acta Physica Polonica A
|
1991
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vol. 79
|
issue 2-3
381-383
EN
We report FIR laser spectroscopy study of Zn_{1-x}Fe_{x}Se (x < 0.06) Semimagnetic Semiconductor at the temperature range of 2-26 K and magnetic fields up to 18T.
2
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Vibronic Effects in EPR Spectra of (NH_{4})_{2}Cu(BeF_{4})_{2}·6H_{2}0 Single Crystal

100%
Hoffmann S., Gomółka-Marciniak M.
Acta Physica Polonica A
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1993
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vol. 83
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issue 6
817-830
EN
Angular variations of the g-factors and linewidth value were recorded at X-band, at room temperature, and at 77 K. The temperature dependence of the g-factors was measured along the principal g-tensor axes in the temperature range from 4.2 K to 300 K. The rigid lattice g-factors at 4.2 K are: g_{z} = 2.428, g_{y} = 2.138, and g_{x} = 2.058. The g_{x} value very slowly increases linearly on heating, whereas g_{z} and g_{y} nonlinearly tend towards their average value. This is a typical behaviour of Cu(II) EPR in Tutton salt crystals, however the g(T) dependence is much less pronounced in (NH_{4})_{2}Cu(BeF_{4})_{2}·6H_{2}0 as compared to the Cu(II) doped salts. The results are described in terms of the two vibronic coupling models of the strong Jahn-Teller effect. It is shown that the models are not adequate to describe the vibronic g-factor behaviour in paramagnetic Cu(II) crystals which is attributed to the cooperative Jahn-Teller effect existing in these crystals.
3
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Characterization of Self-Assembled CdTe/ZnTe Quantum Dots

100%
Kowalik K., Kudelski A., Golnik A., Gaj J., Karczewski G., Kossut J.
Acta Physica Polonica A
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2003
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vol. 103
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issue 6
539-544
EN
We present microluminescence investigations of self-assembled CdTe/ZnTe quantum dots. The dots proprieties resulting from our studies are: values of optical in-plane anisotropy parameters (electron - heavy hole exchange splitting and orientation of anisotropy) and value of effective Lande factor. Parameters giving information about in-plane anisotropy possess random distribution of values with the exchange splitting from 0 to 240 μeV. The effective Lande factor values for our dots are around g^*=-3.2 with a scatter of about 18%. Some PL lines exhibit sudden jumps of energetic position, related to variation of the charge state in their neighborhood.
4
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The Effect of Spin-Orbit Scattering on the Electrical Resistivity of Disordered Materials

100%
Spisak B., Paja A.
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vol. 96
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issue 6
751-758
EN
The spin-orbit scattering of charge carriers is considered as an additional contribution to the potential scattering. The expressions for the effective cross-section and the relaxation time for disordered media are calculated. The results for the Coulomb screened potential are presented and compared with available experimental data.
5
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Optical Γ₆ → Γ₈ Free-to-Bound Transitions in Acceptor δ-Doped Single Heterostructure - Theoretical Analysis

100%
Buczko R., Łusakowski J., Friedland K., Hey R., Ploog K.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1079-1083
EN
A theoretical analysis was carried out of an optical transition observed in high-quality GaAs/AlGaAs heterostructures δ-doped with shallow acceptors. The transition involves a 2D electron and a 3D acceptor-localized hole. The wave functions of a bulk Be acceptor were calculated within the spherical model with both the s-like and d-like parts of the envelope taken into account. The electron envelope wave functions resulted from self-consistent calculations of the electrostatic potential and were dependent on the 2D electron concentration, n_s. We show that: (i) including the d-like part of the acceptor envelope relaxes the selection rules of free-to-bound transitions at k=0;(ii) in the magnetic field, the selection rules depend on the number of the electron Landau level;(iii) the ratio of the intensity of the strongest transitions in both circular polarizations is essentially different from 3:1, and strongly depends on n_s. These results show that a description that neglects the d-like part of the acceptor envelope is both qualitatively and quantitatively unjustified.
6
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Influence of an Electric Field on Fine Properties of III-V and II-VI Quantum Dots Systems

100%
Kowalik K., Krebs O., Kudelski A., Golnik A., Lemaître A., Senellart P., Karczewski G., Kossut J., Gaj J., Voisin P.
Acta Physica Polonica A
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2004
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vol. 106
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issue 2
177-184
EN
We investigate the influence of an electric field on the optical properties of single quantum dots. For sample made of III-V compounds micron-size electro-optical structures were produced in order to apply an electric field in the dot plane. For several individual dots lines significant variations of the anisotropic exchange splitting with the field were observed. On sample made of II-VI compounds we demonstrate the influence of electric field fluctuations on the luminescence of a single quantum dot.
7
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Spectroscopy of Be Acceptor Ground State in GaAs/AlGaAs Heterostructure

100%
Łusakowski J., Buczko R., Sakowicz M., Friedland K., Hey R., Ploog K.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
209-213
EN
Photoluminescence measurements were carried out on Be δ-doped GaAs/Al_{0.33}Ga_{0.67}As heterostructure at 1.6 K in magnetic fields (B) up to 4 T. Luminescence originating from recombination of a two-dimensional electron gas and photoexcited holes localized on Be acceptors was analyzed. The degree of circular polarization (γ_C) of the luminescence from fully occupied Landau levels was determined as a function of B and the two-dimensional electron gas concentration, n_s. At B constant,γ_C decreased with the increase in n_s. The intensity of the optical transition considered was calculated with taking into account s- and d-like parts of the acceptor envelope function. It is shown that the presence of the d-like part explains the observed γ_C(n_s) dependence quantitatively. This shows that polarization spectroscopy on acceptorδ-doped heterostructures enables one to test experimentally the contribution of the L>0 component of the envelope in a shallow acceptor description.
8
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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.
9
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Stark and Zeeman Effects in Nd_{2}Fe_{14}B and Pr_{2}Fe_{14}B Intermetallics

100%
Radwański R., Franse J.
Acta Physica Polonica A
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1996
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vol. 90
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issue 1
223-232
EN
The energy level scheme of the Nd^{3+} and Pr^{3+} ions in ferromagnetic Nd_{2}Fe_{14}B and Pr_{2}Fe_{14}B intermetallic compounds was evaluated on the basis of all known experiments. In calculations the effect of charge (Stark effect) and spin-dependent (Zeeman effect) interactions were taken into account by means of the crystal-field and molecular-field approximation, respectively. The derived energy level scheme is associated with the removal of the degeneracy of the lowest multiplet given by Hund's rules, i.e. ^{4}I_{9/2} (Nd^{3+}) and ^{3}H_{4} (Pr^{3+}). The revealed low-energy electronic structure (<25 meV = 200 cm^{-1}) is associated with many-electron states of the RE^{3+} ions. Magnetic and electronic properties resulting from this fine structure are compared with all known experimental results. The localized crystal electric field levels exist also in Nd_{2}CuO_{4}, an ionic compound which by doping with Ce becomes high-T_{c} superconductor, indicating the formation of crystal electric field states independently on the metallic or ionic state.
10
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Crystal-Field Interactions in RPd_2Al_3 Intermetallics (R = Pr, Nd, Sm, and U)

100%
Radwanski R., Nalecz D., Ropka Z.
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vol. 126
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issue 4a
A-32-A-36
EN
Magnetic and electronic properties of NdPd_2Al_3 have been nicely described with the Nd^{3+} ions within the crystal-field theory revealing that all Nd atoms equally contribute to the temperature dependence of the paramagnetic susceptibility and of the heat capacity with the λ-peak. We consistently described paramagnetic and magnetically-ordered state. The fine electronic structure of the Nd^{3+} ion nicely correlates with the electronic structure of the U^{3+} ion in UPd_2Al_3 giving strong evidence for the trivalent uranium state in the isostructural heavy-fermion superconductor UPd_2Al_3.
11
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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.
12
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Importance of the Spin-Orbit Coupling for 3d-Ion Compounds: the Case of NiO

100%
Radwański R., Ropka Z.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
963-965
EN
The orbital and spin moment of the Ni^{2+} ion in NiO has been calculated at 0 K to be 0.54 μ_{B} and 1.99 μ_{B} respectively. Such large orbital moment, more than 20% of the total moment of 2.53 μ_{B}, proves the need for the "unquenching" of the orbital moment in compounds containing 3d ions. It turns out that the spin-orbit coupling is indispensable for description of magnetic and electronic properties of 3d-ion compounds.
13
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Three Localized f Electrons in UPd₂Al₃ and in UGe₂ Intermetallics

80%
Radwanski R., Nalecz D., Ropka Z.
Acta Physica Polonica A
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2016
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vol. 130
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issue 2
545-550
EN
We have calculated the strength of the excitations between the crystal-field states which are in agreement with inelastic-neutron-scattering results. This agreement confirms the existence in the heavy-fermion superconductor UPd₂Al₃ the crystal-field electronic structure being the finger-print of the U^{3+} ions with three localized f electrons forming strongly-correlated atomic-like quantum system 5f³. The ionic integrity and the low-energy crystal-field electronic structure is preserved in this metallic system in the meV scale as has been postulated in the Quantum Atomistic Solid State theory (QUASST). We provide preliminary results with the U^{3+} ion in UGe₂ showing the ground-state eigenfunction which reproduces the ordered magnetic-moment value of 1.48 μ_{B}. This moment is composed from the dominant orbital contribution (2.6 μ_{B}) and the opposite spin moment (1.12 μ_{B}).
14
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Spin Precession of Quasi-Bound States in Heterostructures with Spin-Orbit Interaction

80%
Isić G., Indjin D., Ikonić Z., Milanović V., Radovanović J., Harrison P.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
513-515
EN
We use a finite-difference model that is capable of describing the single state spin dynamics in a double-barrier AlGaAs heterostructure. The use of Green's functions enables a description of the double-barrier structure by a finite matrix while the interaction with contacts is described by appropriate self-energies. To account for interface roughness scattering, a self-energy Σp_{IR}(E, k) is derived within the random phase approximation. The dominant part is due to in-plane momentum relaxation while a smaller part describing spin-flip scattering is neglected. The former only decreases the state lifetime while the latter can also affect the spin precession frequency.
15
Publication available in full text mode
Content available

Measurement of Very Small Zeeman Splittings in GaN:Mn,Mg by Faraday Rotation

80%
Wołoś A., Kossacki P., Golnik A., Kamińska M., Gaj J., Twardowski A., Grzegory I., Boćkowski M., Porowski S.
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issue 4-5
695-699
EN
In this work we demonstrate an application of Faraday rotation for measuring an extremely small Zeeman splitting of an Mn related absorption line placed at 1.417 eV in optical absorption spectrum of Mn and Mg doped gallium nitride. Analysis of the collected spectra allowed us to determine the value of the splitting as equal to 0.12±0.01 meV at 6 T. This data should help in establishing the nature of the observed absorption band.
16
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Analysis of Emission and Vibronic Transitions in Uranium(3+) Doped Cs_{2}LiYCl_{6} Single Crystals

80%
Karbowiak M., Simoni E., Drożdżyński J., Hubert S.
Acta Physica Polonica A
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1996
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vol. 90
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issue 2
367-370
EN
Uranium(3+) doped single crystals of Cs_{2}LiYCl_{6} with a 0.3 and 2.0% U^{3+} concentration have been obtained by the Bridgman-Stockbarger method. Luminescence spectra of the crystals were recorded at 27 and 15 K, respectively. The emission bands observed in the visible and near infrared regions have been assigned to transitions from the ^{4}I_{11/2}, ^{4}F_{3/2}, and ^{4}G_{7/2} levels to the ^{4}I_{9/2} ground level.
17
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Luminescence and Excitation Spectra of U^{3+} doped RbY_{2}Cl_{7} Single Crystals

80%
Karbowiak M., Murdoch K., Drożdżyński J., Edelstein N., Hubert S.
Acta Physica Polonica A
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1996
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vol. 90
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issue 2
371-376
EN
Uranium(3+) doped single crystals of RbY_{2}Cl_{7} with a uranium concentration of 0.05% and 0.2% were grown by the Bridgman-Stockbarger method using RbU_{2}Cl_{7} as the doping substance. Polished plates of ca. 5 mm in diameter were used for measurements of luminescence and excitation spectra. Since the U^{3+} ions occupy two somewhat different site symmetries, a splitting of all observed f-f bands was observed. The analysis of the spectra enabled definitively an assignment of 22 crystal field bands for both site symmetries as well as the total crystal field splitting of the ground level, equal to 473 cm^{-1} and 567 cm^{-1} for the first and second site symmetry, respectively.
18
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The Influence of Jahn-Teller Effect on Magnetic Properties of Fe-Based Semimagnetic Semiconductors

80%
Lebeckl K., Twardowski A., Liro Z.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
373-375
EN
We report results of calculations of magnetic properties (specific heat, magnetization) of Fe-based Semimagnetic Semiconductors including Jahn-Teller coupling between Fe electronic states and phonons.
19
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Strain Induced k-Linear Spin Splitting in III-V Semiconductors

80%
Skierkowski A., Majewski J.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
455-460
EN
We present theoretical studies of the linear-k strain induced spin splitting of the conduction band in the zinc-blende semiconductors. The studies are based on ab initio calculations performed within the density functional theory with non-scalar relativistic effects fully taken into account. This permits one to construct effective Hamiltonian for the strain induced linear-k spin splitting of the zinc-blende semiconductors. This Hamiltonian reproduces fully the structure of the strain induced linear-k spin splitting and generalizes previously introduced and commonly used effective Hamiltonian.
20
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The Effect of Gd Impurities on the Physical Properties of Half-Metallic Ferromagnet Co_2MnSi

80%
Grasin R., Vinteler E., Bezergheanu A., Rusu C., Pacurariu R., Deac I., Tetean R.
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issue 4
648-651
EN
In this paper we report our experimental and theoretical studies on the effect of Gd impurity on the physical properties of the Heusler half-metallic ferromagnet Co_2MnSi. The analysis of the band structures of the doped alloy shows that the half-metallic properties are completely conserved if Gd substitutes Mn atoms. This effect is not determined by the spin-orbit interaction, but through the coupling between the R(4f) spin with the Mn(3d) itinerant electron spins. We evaluate the strength of such a coupling by calculating, in an ab initio fashion, the total energy of Co_{16}GdMn_7Si_8 compound for a parallel and antiparallel f-d coupling. The obtained magnetic moments of Co or Mn sites are in good agreement with the experimental ones.
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