Search results

1

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

|

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.

2

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.

3

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

|

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.

4

Crystal-Field Interactions in RPd_2Al_3 Intermetallics (R = Pr, Nd, Sm, and U)

100%

Radwanski R., Nalecz D., Ropka Z.

Acta Physica Polonica A

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2014

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vol. 126

|

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.

5

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.

6

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.

7

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.

8

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

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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.

9

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

|

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.

10

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.

11

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.

12

The Effect of Spin-Orbit Scattering on the Electrical Resistivity of Disordered Materials

100%

Spisak B., Paja A.

Acta Physica Polonica A

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1999

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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.

13

Resonant Spin Splitting in III-V Semiconductors

80%

Skierkowski A., Majewski J.

Acta Physica Polonica A

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2005

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vol. 108

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issue 5

867-872

EN

We present first-principles studies of the zero field spin splitting of energy bands in typical III-V semiconductors. Our calculations reveal that the strain induces linear-k spin splitting of the conduction band in theΓ point, which is linear in strain, and determine the magnitude of the so-called acoustic phonon constant that characterizes the magnitude of the spin splitting. In addition, we show that optical phonons lead to spin-flip processes and we present quantitative results for the spin-phonon deformation potentials in GaAs. Most importantly, the calculations show that the linear-k spin splitting can be resonantly enhanced when bands cross in a particular point of the Brillouin zone. This resonant enhancement of the bulk inversion asymmetry coupling constant by more than one order of magnitude was observed in both valence and conduction bands and can be steered by the application of the external stress. This allows tailoring of the spin relaxation and spin precession of conduction electrons in nanostructures to a much larger extent than was hitherto assumed.

14

Oblique Reflection of Electrons from a Potential Barrier in Heterostructures

80%

Pfeffer P., Zawadzki W.

Acta Physica Polonica A

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2014

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vol. 126

|

issue 3

820-827

EN

Reflection of electrons from a potential barrier in heterostructures is described. An electric field of the barrier causes spin splitting of electron energies via the spin-orbit interaction and its form is calculated in the three-level k·p model for a nontrivial case of unbound electrons. It is shown that if the potential barrier is the only source of the spin-orbit interaction, the spin-flip electron reflections are not possible. However, there appear two unexpected possibilities related to the spin-orbit interaction: (a) non-attenuated electron propagation in the barrier whose height exceeds the energies of incoming electrons, (b) total reflection of electrons whose energies exceed barrier's height. It is indicated that the system can serve as a source of spin-polarized electron beams.

15

Electron-Phonon Interaction as a Mechanism of Phase Transition in the CuInP_{2}S_{6} Crystal

80%

Bercha D., Bercha S., Glukhov K., Sznajder M.

Acta Physica Polonica A

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2014

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vol. 126

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issue 5

1143-1145

EN

Studies on the phases of CuInP_{2}S_{6} crystal exhibiting phase transitions of the order-disorder type are performed. A possibility for the cooperative Jahn-Teller effect to occur in this crystal is analyzed. For this purpose, the procedure of constructing the potential energy matrix is generalized for the case of crystal and it is illustrated by the construction of the adiabatic potentials for Γ_{5}-Γ_{5} vibronic coupling for the proto- and paraelectric phases of CuInP_{2}S_{6}. The structure of the obtained potentials is analyzed together with the discussion on the appearance of spontaneous polarization in this crystal.

16

Time-Reversal Invariant Topological Superconductivity in Quasi-One-Dimensional Structures

80%

Mammadova S., Nakhmedov E., Alekperov O.

Acta Physica Polonica A

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2016

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vol. 129

|

issue 4

800-802

EN

It is shown that a time-reversal invariant topological superconductivity can be realized in a quasi-one-dimensional structure, which is fabricated by filling the superconducting materials into the periodic channel of dielectric matrices like zeolite and asbestos under high pressure. The topological superconducting phase sets up in the presence of large spin-orbit interactions when s-wave intra-wire and d-wave inter-wire pairings take place. Kramers pairs of Majorana bound states emerge at the edges of each wire. The time-reversal topological superconductor belongs to DIII class of symmetry with a Z₂ invariant.

17

Crystal Structure and Chemical Characterization of La_{0.7}Sr_{0.3}Mn_{0.7}Ti_{0.3-x}Al_{x}O₃ (0 ≤ x ≤ 0.15) Compounds

80%

Troyanchuk I., Bushinsky M., Tereshko N., Fedotova V., Partyka J.

Acta Physica Polonica A

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2017

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vol. 132

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issue 2

240-244

EN

Neutron powder diffraction and magnetization measurements have been performed for La_{0.7}Sr_{0.3}Mn_{0.7}Ti_{0.3-x}Al_xO₃ (0 ≤ x ≤ 0.15) stoichiometric compounds. Increase of the Al³⁺ content enlarges the Mn⁴⁺ ions fraction from 0% (x=0) up to around 20% (x=0.15). The x=0 composition around 150 K exhibits a structural transition from the rhombohedral phase to the orthorhombic one whereas the crystal structure of the compounds with x=0.1 and 0.15 remains to be rhombohedral down to 2 K. The substitution of Ti⁴⁺ by Al³⁺ ions is accompanied by a gradual increase in the bond angle Mn-O-Mn and decrease in the Mn-O bond length which lead to enhancement of the covalent component of the chemical bond. All these compounds exhibit ferromagnetic components below 100 K. Magnetic moments estimated per manganese from the neutron powder diffraction data are found to be around 1.3 μ_{B} (x=0) and 1.7 μ_{B} (x=0.1 and 0.15) at 2 K. It is suggested that ferromagnetism is originated predominantly from the Mn³⁺-O-Mn³⁺ and Mn³⁺-O-Mn⁴⁺ superexchange interactions whereas bond angles fluctuation leads to magnetic frustrations. Enhancement of covalence slightly increases ferromagnetism.

18

Geometry of the ^4T_{2g} Excited State in Cs_2SiF_6:Mn^{4+}

80%

Reisz A., Avram C.

Acta Physica Polonica A

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2007

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vol. 112

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issue 5

829-833

EN

The aim of this paper is to calculate the equilibrium displacements of the ^4T_{2g} potential surface minimum from the ground state along the a_{1g} and e_g Jahn-Teller active modes for the octahedral [MnF_6]^{2-} cluster obtained by doping Mn^{4+} ions in Cs_2SiF_6 host crystal. The equilibrium displacements in normal and Cartesian coordinates were estimated from force constants of [MnF_6]^{2-} cluster and Huang-Rhys factors associated with the Jahn-Teller stabilization energy. A net equatorial expansion and an axial stretching of the geometry of the [MnF_6]_{2-} cluster in first ^4T_{2g} excited state, as combined effect of the a_{1g} and e_g displacements, were demonstrated.

19

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

|

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}).

20

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.

Refine search results

Influence of an Electric Field on Fine Properties of III-V and II-VI Quantum Dots Systems

Spectroscopy of Be Acceptor Ground State in GaAs/AlGaAs Heterostructure

Application of Generalized Pair Approximation to Diluted Magnetic Semiconductor Quantum Structures

Crystal-Field Interactions in RPd_2Al_3 Intermetallics (R = Pr, Nd, Sm, and U)

Stark and Zeeman Effects in Nd_{2}Fe_{14}B and Pr_{2}Fe_{14}B Intermetallics

Band Mixing Effects in Quantum Well Magnetoexcitons

Importance of the Spin-Orbit Coupling for 3d-Ion Compounds: the Case of NiO

Submilimeter Magnetospectroscopy on ZnFeSe

Vibronic Effects in EPR Spectra of (NH_{4})_{2}Cu(BeF_{4})_{2}·6H_{2}0 Single Crystal

Characterization of Self-Assembled CdTe/ZnTe Quantum Dots

Optical Γ₆ → Γ₈ Free-to-Bound Transitions in Acceptor δ-Doped Single Heterostructure - Theoretical Analysis

The Effect of Spin-Orbit Scattering on the Electrical Resistivity of Disordered Materials

Resonant Spin Splitting in III-V Semiconductors

Oblique Reflection of Electrons from a Potential Barrier in Heterostructures

Electron-Phonon Interaction as a Mechanism of Phase Transition in the CuInP_{2}S_{6} Crystal

Time-Reversal Invariant Topological Superconductivity in Quasi-One-Dimensional Structures

Crystal Structure and Chemical Characterization of La_{0.7}Sr_{0.3}Mn_{0.7}Ti_{0.3-x}Al_{x}O₃ (0 ≤ x ≤ 0.15) Compounds

Geometry of the ^4T_{2g} Excited State in Cs_2SiF_6:Mn^{4+}

Three Localized f Electrons in UPd₂Al₃ and in UGe₂ Intermetallics

Spin Precession of Quasi-Bound States in Heterostructures with Spin-Orbit Interaction