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  1. 30 Acta Physica Polonica A

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  1. 30 Ivanov V.

  2. 21 Godlewski M.

  3. 5 Khachapuridze A.

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1
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SU(2) Coherent State Path Integral Investigation of the Holstein Dimer

100%
Hakioğlu T., Ivanov V., Zhuravlev M.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
927-930
EN
The SU(2) coherent state path integral is used to investigate the partition function of the Holstein dimer. This approach naturally takes into account the dynamical symmetry of the model. The ground-state energy and the number of the phonons are calculated as functions of the parameters of the Hamiltonian. The renormalizations of the phonon frequency and electron hopping for bonding and antibonding states are considered. The destruction of quasiclassical mean field solution is discussed.
2
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Spin Hall Effect in a Two-Dimensional Electron Gas with Strong Rashba Spin-Orbit Interaction: Semiclassical Keldysh Approach

100%
Dyrdał A., Barnaś J., Ivanov V., Dugaev V.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1059-1061
EN
Spin Hall effect in a two-dimensional electron gas with the Rashba spin-orbit interaction is analyzed theoretically. We use the Keldysh technique for nonequilibrium processes, modified in order to take into account well-defined splitting of the Fermi surface due to strong spin-orbit coupling. Using such an approach, we reconsider the two-dimensional electron gas with the Rashba spin-orbit interaction and show that impurity scattering processes suppress the spin Hall effect.
3
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Magnetic Properties of the RT_{2}X_{2}, RTX_{2} and RTX Compounds in High Magnetic Fields

100%
Szytuła A., Ivanov V., Vinokurova L.
Acta Physica Polonica A
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1994
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vol. 85
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issue 2
293-296
EN
Magnetization curves up to 140 kOe have been measured in the temperature range 4.2-100 K on polycrystalline oriented samples for some RT_{2}X_{2}, RTX_{2} RTX compounds. The magnetic phase diagrams for all samples are determined.
4
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Spin Relaxation Processes in Quantum Well Structures of Cd_{1-x}Mn_xTe/Cd_{1-x}Mg_xTe

100%
Khachapuridze A., Ivanov V., Godlewski M., Karczewski G.
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issue 4-5
643-648
EN
Fast spin relaxation of Mn^{2+} ions in a magnetic quantum well of CdMnTe with 1% Mn fraction is related to a very efficient spin-flip interaction between Mn ions and free carriers. This mechanism of spin relaxation becomes dominant at increased excitation densities. The observed response of the photoluminescence bands to the Mn^{2+} magnetic resonance indicates that free carriers are heated at the magnetic resonance conditions. A decrease in formation/recombination rates of free and trion excitons is observed. Donor bound exciton photoluminescence is enhanced, which we relate to delocalization of free excitons, caused by interaction with microwave heated free carriers.
5
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Magnetic Properties of NdCo_{2}Si_{2}, TbCo_{2}Si_{2} and DyCo_{2}Si_{2} in High Magnetic Fields

100%
Ivanov V., Vinokurova L., Szytuła A.
Acta Physica Polonica A
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1992
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vol. 81
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issue 6
693-698
EN
The magnetic properties of RCo_{2}Si_{2} (R = Nd, Tb, Dy) compounds were studied by measuring the high-field magnetization in magnetic fields up to 140 kOe and over the temperature range 4.2-45 K. The magnetic field induces in NdCo_{2}Si_{2} three metamagnetic phase transitions and two transitions in TbCo_{2}Si_{2} and DyCo_{2}Si_{2} compounds.
6
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Luminescence of Cd0.7Mn0.3Te Crystals in Transverse Magnetic Field

100%
Brazis R., Barauskaitė L., Ivanov V., Godlewski M.
Acta Physica Polonica A
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2006
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vol. 109
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issue 6
731-741
EN
Photoluminescence of cleaved Cd0.7Mn0.3Te crystals is studied at T≈1.6 K at the normal- and oblique (45º) incidence of the pumping Ar laser beam (λ=488 nm) in magnetic fields -7≤ B≤7 T in the Voigt geometry. At B=0, photoluminescence maximum is found at 2.0819 eV at normal incidence (and backward emission) whereas the oblique incidence and emission shows photoluminescence maximum intensity at 2.0536 eV. The red shift of photoluminescence maximum position with the rise in B is observed and the results are found to be in good agreement with sp-d exchange interaction model for the oblique incidence case. Backward emitted photoluminescence line is found to narrow from 26.2 to 23.5 meV with the rise in B from 0 to 7 T. Alloy disorder contribution exhibits opposite trend to broaden, as is calculated on the basis of the matrix of the energy gap dependence on x and B. Therefore the observed photoluminescence line narrowing is assigned to the suppression of magnetic fluctuation in magnetic field. A linear size of magnetic fluctuation is estimated to be about 1/5 of the free exciton diameter. Photoluminescence maximum position difference in the normal- and oblique incidence cases is assigned to polaritons.
7
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Comparison of Microscopic Mechanisms of Blue Anti-Stokes Luminescence in Undoped and Chromium Doped ZnSe Crystals

100%
Ivanov V., Omel'chuk A., Godlewski M.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
365-368
EN
Anti-Stokes luminescence is observed in chromium doped and in undoped ZnSe crystals. In the former case anti-Stokes luminescence is due to two complementary ionization transitions of Cr ions. In the latter case two-photon absorption becomes important at a high excitation density.
8
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Influence of Magnetic Field on Blue Anti-Stokes Luminescence of ZnSe:Cr Crystals

100%
Ivanov V., Semenov Y. G., Surma M., Godlewski M.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
821-824
EN
The results of photoluminescence and magneto-luminescence studies of chromium doped ZnSe crystals are presented for blue colour shallow donor-shallow acceptor pair photoluminescence, with a zero phonon line at 2.692 eV. This donor-acceptor pair photoluminescence is observed under photo-excitation with photon energies smaller than the emission energy (anti-Stokes luminescence) and dominates in the photoluminescence spectrum of ZnSe:Cr at the excitation energy about 2.41 eV and for temperature T<20 K. A quantum efficiency of this anti-Stokes luminescence is relatively large. It is of about 10^{-3} at 0 T and increases with increasing magnetic field up to 7 T at temperature T=2 K. We relate the intensity of the anti-Stokes luminescence to a non-equilibrium concentration of photo-excited Cr^{+} ions and propose that the rate of spin-dependent recombination of Cr^{+} ions with free holes (decreases with increasing magnetic field) is responsible for the observed increase in the anti-Stokes luminescence intensity at higher magnetic fields.
9
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Band Edge Energies Pinning in Magnetic Field in Semimagnetic Cd_{0.7}Mn_{0.3}Te

100%
Barauskaitė L., Brazis R., Ivanov V., Godlewski M.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6
1056-1060
EN
Results of Cd_{0.7}Mn_{0.3}Te magneto-photoluminescence investigations are analyzed. Photoluminescence was measured in a Voigt geometry at the temperature of 1.6 K. Two models describing radiative transition energy are compared with the experimental results of Cd_{0.7}Mn_{0.3}Te luminescence. The energy of recombination transition, employing the complete form of band states splitting description (term due to the Landau splitting included), shows deviation from experiment at B > 2 T. Two possible reasons of discrepancies from the experiment - exchange interaction constants dependence on magnetic field or band edge energies pinning in magnetic field - are discussed. Band edge energies pinning in magnetic field is related to the hybridization of Mn 3 d^{5} levels with the band states of the host. We determine the corrected values of exchange interaction constants (N_0 α -N_0 β/3) at magnetic fields B < 5 T.
10
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Optical Characterization of ZnO Nanorods Grown by the Ultra-Fast and Low Temperature Hydrothermal Process

88%
Witkowski B., Ivanov V., Wachnicki Ł., Gierałtowska S., Godlewski M.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1199-1201
EN
The results of photoluminescence investigations of zinc oxide nanorods are reported. These nanorods grown on undoped silicon substrates were obtained by low temperature and ultra-fast version of a microwave-assisted hydrothermal method. The photoluminescence investigations show very high quality of the obtained material. From photoluminescence studies we conclude the lack of carrier localization effects. The photoluminescence is dominated by band gap edge emission of bound excitonic (donor bound excitons) origin. Thus, the photoluminescence quenching observed at increased temperatures is associated with thermal ionization of shallow donors. From photoluminescence analysis (changes of photoluminescence line width) a strength of exciton-acoustic phonon coupling is evaluated.
11
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Electronic and Transport Properties of Ragsn (R=Ce,Pr,Nd,Dy) Compounds

88%
Fus D., Ivanov V., Jezierski A., Penc B., Szytuła A.
Acta Physica Polonica A
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2000
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vol. 98
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issue 5
571-586
EN
The electronic structure of the ternary RAgSn (R=Ce,Pr,Nd,Dy) compounds which crystallize in the hexagonal LiGaGe-type structure was studied by X-ray photoemission spectroscopy. Core-levels and valence bands were investigated. The X-ray photoemission spectroscopy valence bands are compared with the ones calculated using the spin-polarized tight-binding linear muffin-tin orbital method. The obtained results indicate that the valence bands are mainly determined by the Ag 4d band. The spin-orbit splitting values Δ_{SO} determined from the XPS spectra of 3d_{5/2} and 3d_{3/2} are equal to 18.8eV for R= Ce, 20.2eV for R = Pr and 22.6eV for R = Nd. The analysis of these spectra on the basis of the Gunnarsson-Schönhammer model gives a hybridization of f orbitals with the conduction band. The calculation of the total energy for two models of the crystal structure: an ordered of the LiGaGe-type and a disordered one of the CaIn_{2}-type indicate that in these compounds the LiGaGe-type structure is stable. Additionally, the temperature dependences of the electrical resistivity of CeAgSn and DyAgSn are investigated. At high temperatures the resistivity is not a linear function of temperature which indicates an electron-phonon interaction in the presence of a small s-d scattering, whereas at low temperatures anomalies connected with the magnetic phase transitions are observed.
12
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Time-Resolved Microwave Spectroscopy of High Electron Mobility GaAs/AlGaAs Structures

88%
Khachepuridze A., Ivanov V., Godlewski M., Regiński K., Bugajski M.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
387-391
EN
Mechanism of the optical detection of cyclotron resonance via emission from 2D electron gas in modulation doped quantum wells and in high electron mobility structures of GaAs/AlGaAs is discussed based on the results of time-resolved optical detection of cyclotron resonance. An important role of impact ionization processes is demonstrated. We also show that microwave radiation destroys emission enhancement at the Fermi level and the relevant mechanism is proposed.
13
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Role of Auger-Type Energy Transfer Processes in Quenching of Anti-Stokes Emission in Chromium and Iron Doped ZnSe: ODMR, Optical and Time-Resolved Study

76%
Ivanov V., Karczewski G., Godlewski M., Omel'chuk A., Belyaev A., Zhavoronkov N.
Acta Physica Polonica A
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2003
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vol. 103
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issue 6
695-701
EN
Energy up-conversion in chromium and iron doped ZnSe results in the appearance of an anti-Stokes luminescence. The process is efficient in ZnSe:Cr, but not in ZnSe:Fe. We conclude that very efficient three-center Auger processes in ZnSe:Fe quench the anti-Stokes luminescence emission. For chromium doped samples influence of the Auger mechanism is weaker, which we explain by less efficient carrier retrapping by Cr ions. We further discuss possibility of efficient pumping of infrared Cr-related emissions via Cr photoionization transition.
14
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Comparison of Exciton Properties in Quantum Well Structures of ZnCdSe/ZnSe and ZnSe/ZnMgSSe

76%
Godlewski M., Ivanov V., Bergman J., Monemar B., Leonardi K., Behringer M., Hommel D.
Acta Physica Polonica A
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1998
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vol. 94
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issue 2
313-316
EN
Properties of excitons in quantum well structures of ZnCdSe/ZnSe and ZnSe/ZnMgSSe are compared. In ternary ZnCdSe quantum wells and at low temperature excitons are strongly localised. Weaker localization is observed in quantum well structures of ZnSe/ZnMgSSe. Present studies suggest formation of negatively charged excitons in the latter structures.
15
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Investigation of Photoelectric Properties of ZnSe:Cr and ZnTe:V:Al by Picosecond Four-Wave Mixing Technique

76%
Kadys A., Sudzius M., Jarasiunas K., Ivanov V., Godlewski M., Launay J.
Acta Physica Polonica A
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2004
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vol. 105
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issue 6
651-657
EN
Role of deep impurity levels in carrier generation, transport, and recombination were investigated in bulk ZnSe:Cr and ZnTe:V:Al crystals by four-wave mixing technique. The temporal and exposure dependencies of optical nonlinearities in ZnSe:Cr evidenced an influence of Cr1+/Cr2+ states in carrier generation, exhibited very fast carrier relaxation, and revealed the presence of competing recombination mechanisms. Similar investigations in ZnTe:V:Al showed an effective carrier generation from Al-induced defect complexes as well as very fast carrier capture by Zn-vacancies.
16
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Structure, Surface Morphology and Optical Properties of Thin Films of ZnS and CdS Grown by Atomic Layer Epitaxy

76%
Szczerbakow A., Godlewski M., Dynowska E., Ivanov V., Świątek K., Goldys E., Phillips M.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
579-582
EN
In this communication we report successful growth of monocrystalline cubic ZnS and monocrystalline and polycrystalline cubic and wurtzite films of CdS by atomic layer epitaxy. Structural and optical properties of these films are analysed. ZnS (and CdS/ZnS) films grown on GaAs substrate are cubic. Atomic layer epitaxy grown films provide several advantages over ZnS and CdS materials grown by other techniques, especially compared to bulk material, which is grown at higher temperatures. First results for ZnS/CdS/ZnS quantum well structures are also discussed.
17
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Optically Pumped Mid-Infrared Stimulated Emission of ZnSe:Cr Crystals

76%
Ivanov V., Godlewski M., Szczerbakow A., Omel'chuk A., Davydov A., Zhavoronkov N., Raciukaitis G.
Acta Physica Polonica A
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2004
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vol. 105
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issue 6
553-558
EN
We demonstrate that ZnSe:Cr is an excellent solid state laser material for mid-infrared region with a broad amplification band from 2.2 μm to 3 μm, and with a high quantum efficiency of a radiative recombination. 46% external total efficiency and 56 mW threshold power were achieved, when pumped with a CW YAlO:Ho laser at resonant excitation conditions. Such laser system can have widespread applications in medicine as laser scalpels with regulated cutting depth. We further demonstrate a stimulated emission under Cr2+ to 1+ photo-ionization pumping. The latter opens chances for laser emission under carrier injection conditions.
18
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Preparation of Nanocomposite Magnetic Compounds Based on Layered Semiconductors by Means of Electrochemical Intercalation in a Gradient Magnetic Field

76%
Boledzyuk V., Bakhtinov A., Kovalyuk Z., Kudrynskyi Z., Ivanov V., Slyn'ko V.
Acta Physica Polonica A
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2016
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vol. 130
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issue 3
773-777
EN
In this paper we propose a method of intercalation of layered single crystals with atoms of 3d-metals in a magnetic-field gradient. We report on structure properties of Co_{x}InSe and Co_{x}In₂Se₃ layered crystals intercalated by cobalt. It was established that ferromagnetic ordering at room temperature is observed in the intercalated crystals. The crystals are a nanocomposite material that consists of a layered matrix and arrays of Co nanoformations on the van der Waals surfaces of InSe and In₂Se₃ layers.
19
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Photoemission Electronic States of (Mn_{1-x}Fe_x)_5Si_3

76%
Penc B., Zalecki R., Jezierski A., Szytuła A., Kołodziejczyk A., Ivanov V.
Acta Physica Polonica A
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2005
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vol. 107
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issue 6
967-976
EN
The core-level and valence band electronic states studies of single crystalline transition metal silicides (Mn_{1-x}Fe_x)_5Si_3 (x=0 and 0.05) by the X-ray and ultraviolet photoemission spectroscopies are reported. The Mn 2p core-level spectra for both compounds were ascribed to the relevant Mn sites in their crystal structure. The valence band spectra were compared with the result of ab-initio band calculations using the tight-binding linear muffin-tin orbital method. It was concluded that the enhancement of the spectral density within the 2 eV binding energy region below the Fermi energy comes from the effect of strongly correlated Mn 3d electrons.
20
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Mechanism of Radiative Mn^{2+} Intra-Shell Recombination in Bulk ZnMnS

76%
Ivanov V., Godlewski M., Yatsunenko S., Khachapuridze A., Li M., Gołacki Z.
Acta Physica Polonica A
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2001
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vol. 100
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issue 3
351-355
EN
Origin of a fast component of the photoluminescence decay of Mn^{2+} intra-shell ^4T_1 → ^6A_1 transition is discussed based on the results of photoluminescence, photoluminescence kinetics and optically detected magnetic resonance experiments performed for bulk ZnMnS samples with about 1% Mn fraction. It is demonstrated that a fast component of the photoluminescence decay, reported previously for quantum dot structure and related to quantum confinement effects, is also observed in bulk samples and is related by us to very efficient spin cross-relaxation effects.
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