Full-text resources of PSJD and other databases are now available in the new Library of Science.
Visit https://bibliotekanauki.pl
Preferences help
Polish version English version Language
enabled [disable] Abstract
Number of results

Results found: 19

Number of results on page
first rewind previous Page / 1 next fast forward last

Search results

Search:
in the keywords:  71.38.+i
help Sort By:

help Limit search:
first rewind previous Page / 1 next fast forward last
1
Content available remote

Solitons in a One-Dimensional Degenerate Hubbard Model

100%
Lipiński S.
Acta Physica Polonica A
|
1991
|
vol. 80
|
issue 1
117-128
EN
An effective magnon-lattice Hamiltonian for the degenerate Hubbard chain with electron-phonon interaction is derived and a formalism for the description of solitary magnons is presented.
2
Content available remote

Application of Photomemory Effect in Cd_{1-x}Mn_{x}Te_{1-y}Se_{y}:In for Direct Measurements of Magnetization of Bound Magnetic Polarons

100%
Wojtowicz T., Koleśnik S., Miotkowski I., Furdyna J.
Acta Physica Polonica A
|
1992
|
vol. 82
|
issue 4
637-640
EN
The first direct measurement of the magnetization of donor bound magnetic polarons in diluted magnetic semiconductors is reported. The experiment has been performed taking advantage of photomemory effect found in n-type Cd_{1-x}Mn_{x}Te_{1-y}Se_{y} crystals doped with In. Good agreement between experimental results and theory of bound magnetic polarons is observed.
3
Content available remote

Ground State Phase Diagram of Mixed-Stack Compounds with Intermolecular Electron Transfer

100%
Luty T.
Acta Physica Polonica A
|
1995
|
vol. 87
|
issue 6
1009-1021
EN
The ground state energy for a chain of donor and acceptor molecules (mixed-stack architecture) is calculated within the three-state model. The model describes the intermolecular electron transfer and, in particular, stres­ses the role of the diagonal coupling of the electron to symmetry breaking molecular displacements and the local electric field. The modulation of the in­termolecular Coulomb interaction is shown to have important consequences for the ground state and its dynamics. In particular, the ground state en­ergy as a function of the displacement may show one, two or three minima with varied molecular ionicity. An analysis of the function gives a phase diagram which indicates a possibility for the coexistence of neutral (undis­torted) and ionic (distorted) chains of molecules in the ground state. The function is illustrated by numerical calculations with parameters appropriate for the tetrathiafulvalene-chloranil crystal which undergoes a neutral-to-ionic phase transition induced by either temperature or pressure. The effect of the electron transfer on the lattice dynamics of the mixed-stack system is briefly considered. It is suggested that the thermodynamical phase diagram for tetrathiafulvalene-chloranil system can be understood as a result of two effects: pressure induced quantum mixing between diabatic states which de­termine a nature of components and temperature stimulated classical mixing of the components.
4
Content available remote

Shallow-Deep Instability of Donor States in Many-Valley Semiconductors

100%
Grinberg M.
Acta Physica Polonica A
|
1991
|
vol. 80
|
issue 3
361-364
EN
The shallow-deep instability of double and single donors in multi-valley semi conductors using the model Hamiltonian is studied. The obtained results describe properly the properties of double donors (in D^{0} and D^{+} state) in Ge and single deep donors in Al_{x}Ga_{1-x}As for 0.3 < x < 0.5.
5
Content available remote

Shallow Donors and Acceptors in GaN; Bound Excitons and Pair Spectra

80%
Stępniewski R., Wysmołek A.
Acta Physica Polonica A
|
1996
|
vol. 90
|
issue 4
681-690
EN
Recent photoluminescence results obtained for homoepitaxial GaN layers are presented. Dominant photoluminescence structures observed for these layers can be assigned to excitons bound to neutral impurities. Different methods such as temperature dependent evolution, high magnetic field and time resolved spectroscopy have been used to study the exciton line properties. For the p-type samples sharp lines are observed, assigned to the donor-acceptor recombination for differently distant pairs. The analysis of the optical transitions related to donors and acceptors is in reasonable agreement with the effective mass approximation. Electron phonon interaction was found to strongly affect the optical properties of GaN. The dominant intrinsic defect has been identified as a donor located at a nitrogen site.
6
Content available remote

Influence of Bound Magnetic Polarons on Magnetic and Electrical Properties in Metallic n-Cd_{0.95}Mn_{0.05}Se

80%
Głód P., Sawicki M., Dietl T., Skośkiewicz T., Lenard A., Plesiewicz W.
Acta Physica Polonica A
|
1995
|
vol. 87
|
issue 1
173-175
EN
Doping-induced contribution to the millikelvin magnetic susceptibility of Cd_{0.95}Mn_{0.05}Se:In has been found to undergo a maximum at n ≈ 2n_{c}, and to vanish for n ≥ 8n_{c}, where n_{c} is the electron concentration corre­sponding to the metal-insulator transition. This confirms the presence, also in the metallic phase, of bound magnetic polarons. Their slow dynamics may account for hysteresis visible in our magnetoresistance data.
7
Content available remote

Thermodynamics of Pseudospin-Electron Model in the U=0 Limit

80%
Stasyuk I., Shvaika A., Tabunshchyk K.
Acta Physica Polonica A
|
2000
|
vol. 97
|
issue 3
411-414
EN
Analytical consideration of a pseudospin-electron model in the absence of electron correlations is presented. Pseudospin and electron number mean values, thermodynamic potential, pair correlation functions are obtained in the same self-consistent approximation. The possibility of either first or second order phase transitions between different uniform phases (bistability) as well as between the uniform and the chessboard one is shown. In the regime n=const, an instability with respect to phase separation can take place.
8
Content available remote

On the Anharmonic Polaronic Model

80%
Konior J.
Acta Physica Polonica A
|
1992
|
vol. 82
|
issue 5
773-776
EN
Anharmonic polaronic model is considered. The model consists of the electronic subsystem, described within the extended Hubbard model, coupled to anharmonic local phonons. By the canonical Holstein-Lang-Firsov transformation the electron-phonon interaction term is ruled out and, then, the effective electronic Hamiltonian is obtained by averaging over the ground state of the phononic subsystem. It is shown that anharmonicity introduces two main additional factors as compared with the harmonic case. First, the band narrowing factor is less rapidly decaying function of the electron-phonon interaction strength. Second, anharmonicity introduces further renormalization of the on- and intersite interaction between fermions.
9
Content available remote

Towards a Unified View of Electron-Phonon Coupling in 1D Solids

80%
Girlando A., Painelli A., Soos Z.
Acta Physica Polonica A
|
1995
|
vol. 87
|
issue 4-5
735-742
EN
We analyze the effect of on-site and on-bond electron-phonon (e-ph) coupling in different classes of quasi one-dimensional (1D) solids in terms of a single model. The model was originally developed to account for e-ph coupling in charge transfer crystals and to interpret their vibrational spectra. The same model is extended to conjugated polymers, showing that important information about the electronic structure can be obtained through a careful analysis of vibrational data. Evidence of e-ph coupling in the spectra of halogen-bridged transition-metal complexes is also presented. The unified model thus applies to different classes of 1D systems and yields transferable e-ph coupling constants.
10
Content available remote

Binding Energy of a Bound Polaron in a Quantum Well Wire

80%
Bouhassoune M., Charrour R., Fliyou M., Bria D., Nougaoui A.
Acta Physica Polonica A
|
2000
|
vol. 98
|
issue 1-2
111-122
EN
Theoretical study of the binding energies of an off-center donor hydrogenic impurity in a cylindrical quantum well wires semiconductor is presented. Calculations are performed in the framework of the effective mass approximation using the variational approach. We describe the effect of the quantum confinement by an infinitely deep potential well and we take into consideration the interaction between the charge carrier (electron and ion) and the optical phonons (confined longitudinal optical and surface optical). Our results show that the impurity binding energy depends strongly on the spatial confinement, the impurity position and the polaronic corrections.
11
Content available remote

Excitonic Instabilities of Deformable Lattice - from Self-Trapping to Phase Transition

80%
Toyozawa Y.
Acta Physica Polonica A
|
1995
|
vol. 87
|
issue 1
47-56
EN
The optically created exciton will be self-trapped if its coupling to phonons is strong enough, and will moreover be self-decomposed if the elec­tron and the hole couple to phonons in an opposite way. The bistability between the parity-conserved and parity-broken self-trapped excitons was observed in alkali halides. The situation is most dramatic if the bistability between the parity-broken self-trapped exciton and the ground state (with no exciton) comes into play since the electron-hole pairs may then be sponta­neously generated at every lattice site, resulting in the electronic and struc­tural phase transition. The neutral to ionic phase transition observed in a few organic charge transfer compounds under applied pressure or decreasing tem­perature can be considered as an example. Recent experiment revealed that TTF-chloranil, among others, is subject to photo-induced transient phase change over hundreds of unit cells per one photon. The dynamics of this process can be described in terms of self-trapping and self-multiplication of a photo-generated charge transfer exciton along the chain through the at­tractive dipolar interaction. This description of phase transition in terms of exciton dynamics will provide a new paradigm of materiology.
12
Content available remote

The Polaron Scenario for High-T_{c} Superconductivity

80%
Ranninger J.
Acta Physica Polonica A
|
1994
|
vol. 85
|
issue 1
89-102
EN
On the basis of experimental evidence we conclude that high-Tc superconducting materials are composed of two distinct subsystems: one in which electrons are bound together in form of localized pairs of small polarons (bipolarons) and one in which electrons exist as strongly correlated Fermions. Upon doping one passes at a critical doping rate from the insulating parent compounds to metallic compounds. There, a charge transfer mechanism between the two subsystems sets in abruptly by which bipolarons can decay into pairs of electrons and vice versa. Such a picture can be modelled by a mixture of interacting Bosons and Fermions. A superconducting ground state for such a system develops at low temperature which is characterized by the opening of a gap in the single electron spectrum and the appearance of collective Boson excitations with a linear spectrum which is confined to the energy regime of the gap. Above T_{c}, a pseudo-gap remains upon closing the superconducting gap. There are strong indications that the normal state has non Fermi liquid behaviour.
13
Content available remote

Polaron Effect on the Binding Energy of Shallow Donor in Cylindrical Quantum Dot

80%
Charrour R., Bouhassoune M., Bria D., Nougaoui A., Fliyou M.
|
|
vol. 96
|
issue 6
759-768
EN
In the framework of the effective-mass approximation and the modified Lee-Low-Pines variational method, we present a theoretical study of the effect of the confined longitudinal-optical phonon and two types of surface-optical phonon (top and side mode) on the binding energy of shallow donor in cylindrical quantum dot. The effect of quantum confinement is described by an infinitely deep potential well. The impact of these different phonon modes is important and depends on the dimension of the quantum dot.
14
Content available remote

Formation of the DX State by Donors in Al_{x}Ga_{1-x}As - Experiment

80%
Dobaczewski L., Kaczor P., Missous M., Żytkiewicz Z., Dobosz D., Peaker A.
Acta Physica Polonica A
|
1992
|
vol. 82
|
issue 5
905-907
EN
A high-resolution Laplace-transform deep level transient spectroscopy was used to study electron emission from the DX centres related to group IV and VI donor elements in AlGaAs. This provides the experimental evidence that substitutional-interstitial atom motion is responsible for DX behaviour and for the associated metastability effects.
15
Content available remote

Polaron Problem in Quantum Wells

80%
Bardyszewski W., Prywata M.
Acta Physica Polonica A
|
1995
|
vol. 88
|
issue 5
969-973
EN
The effect of polar interaction between an electron in a quantum well and bulk longitudinal optical phonons is analysed. Electron spectral density function is calculated in the lowest order cumulant approximation. The position and linewidth of the quasiparticle peak are obtained as a function of quantum well width and temperature.
16
Publication available in full text mode
Content available

Analysis of Possible Scattering Processes for Bloch Positronium in Ionic Crystals at Elevated Temperatures

80%
Bondarev I.
Acta Physica Polonica A
|
2001
|
vol. 99
|
issue 3-4
337-343
EN
The role of nonpolar optic phonon scattering and of umklapp acoustic phonon scattering is analyzed for a delocalized positronium atom in ionic crystals at elevated temperatures. At temperatures above which they become essential both of these scattering mechanisms contribute to the imaginary self-energy of positronium renormalizing its acoustic deformation potential constant. It was such a renormalization that was recently observed experimentally for delocalized positronium in MgF_2 crystal. We put forward the theoretical explanation of these experiments based upon the model of nonpolar optic phonon scattering of positronium. An effect analogous to that observed in MgF_2 is predicted for crystalline quartz above the temperature of (α-β)-phase transition.
17
Content available remote

Spectroscopic Investigations of Charge Transfer Salt VINΦ_{2}(TCNQ)_{2}

80%
Łapiński A., Świetlik R., Strzelecka H., Veber M.
Acta Physica Polonica A
|
1995
|
vol. 87
|
issue 4-5
835-841
EN
VINΦ_{2}(TCNQ)_{2} is a salt with two different, non-parallel TCNQ stacks. The polarized reflectance spectra from single crystals in the IR region 660-5200 cm^{-1}, the powder absorption spectra 400-45000 cm^{-1} and FT-NIR Raman spectra of VINΦ_{2}(TCNQ)_{2} are measured at room temperature. More­over, the temperature dependence of powder absorption spectra in the fre­quency range 400-7900 cm^{-1} are studied. The nature of electronic bands, the anisotropy of optical conductivity, the temperature dependence of some vibrational bands and the charge distribution on different TCNQ stacks are discussed.
18
Content available remote

Scattering of Excitons by Phonons in Quantum Wells

80%
Bardyszewski W., Prywata M.
Acta Physica Polonica A
|
1996
|
vol. 90
|
issue 4
715-718
EN
A method to describe the effects of the exciton-optical phonon interaction is presented using the cumulant expansion approximation. The functional-integral technique of coherent phonon states is used in order to justify the commonly used model Hamiltonian and generate the proper perturbation series. The influence of the mutual electron-hole screening on the polaronic effects in quantum wells is analyzed.
19
Content available remote

Physics of Neutral-to-Ionic Phase Transition in Organic Charge Transfer Semiconducting Compounds

80%
Cailleau H., Lemée-Cailleau M. H., Le Cointe M., Luty T.
Acta Physica Polonica A
|
1997
|
vol. 92
|
issue 4
597-608
EN
An uncommon excitonic instability takes place in some exotic semiconducting compounds. Indeed, the equilibrium neutral-to-ionic (N-I) phase transition, as well as the non-equilibrium photo-induced phase transformation, observed in some organic charge-transfer complexes, originate from intra- and inter-chain cooperative effects between structurally relaxed charge-transfer excitations. This electronic-structural phase transition manifests itself by a change of the degree of charge-transfer and a dimerization distortion with the formation of donor-acceptor pairs along the stacking axis in the I phase. Thermal charge-transfer excitations associated with the formation of I strings along N chains are at the heart of the mechanism of this phase transition. These relaxed electronic excitations, which are an intrinsic feature of low-dimensional systems with strong electron-phonon coupling, can be described in terms of self-trapping and self-multiplication of charge-transfer excitons. Precise structural studies on the prototype compound, tetrathiafulvalene-p-chloranil allow to highlight the respective role taken by the ionicity and the dimerization. Symmetry and thermodynamics analysis of the N-I transition, based on recent determination of the pressure-temperature phase diagram, make possible to present a consistent picture of this phase transition. Supported by theoretical considerations taking into account the interplay between quantum and thermal effects, the experimental observations show that the N-I transition results from the condensation and the ordering (crystallization) of charge-transfer excitations, following a phase diagram analogous to the solid-liquid-gas one.
first rewind previous Page / 1 next fast forward last
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.