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1
Content available remote

Corner Dissipation in Quantum Hall Systems

100%
Riess J., Magyar P.
Acta Physica Polonica A
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1993
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vol. 84
|
issue 3
523-526
EN
A description of the onset of dissipation in the integer quantum Hall effect is given, where the electric field across the sample is expressed through a time dependent vector potential. This brings the essentially time dependent, non-stationary nature of the problem into focus. The electric field induces transitions between the levels of the disorder broadened Landau band. Above a critical electric field the particles are driven upwards in energy space beyond the Fermi level, which leads to dissipation since the accumulated energy is lost to the heat bath after τ_{in}, the time between two inelastic events. Thus the dissipated power is obtained without the use of the traditional (linear response) transport formulae. As an application we investigate the dissipation in the corner region of a Hall bar. The results are in reasonable accordance with recent experiments exploiting the fountain pressure effect.
2
Content available remote

Quantum Model for Metal-Insulator Transition in Amorphous Gd_{x}Si_{1-x}

80%
Paja A., Ornat M.
Acta Physica Polonica A
|
2013
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vol. 124
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issue 4
717-719
EN
The model for experimentally observed metal-insulator transition induced by magnetic field in amorphous Gd_{x}Si_{1 - x} is presented. The method of calculation is based on the previously created model for amorphous alloys now developed to include magnetic field effects. The model is based on the quantum "2 k_{F}" scattering model theory where the pseudopotentials are replaced by the scattering matrix operators and the Fermi energy is properly determined by the accurate values of the phase shifts. The results agree very well with experimental data.
3
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The Néel Magnetic Relaxation Dynamics in Nanoparticle Systems - Phenomenological Approach versus Stochastic Approach

80%
Osaci M.
Acta Physica Polonica A
|
2016
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vol. 129
|
issue 3
323-328
EN
In nanomagnetism, the studies of magnetic nanoparticle systems are of particular interest from both experimental and theoretical points of view. Experimentally, the measurements made on such a system are hard to interpret. It is very difficult to distinguish the effect of the magnetic dipole interactions from the effects of size distribution or effective magnetic anisotropy constants. In this respect, the simulation models can help. This paper presents a study comparing the two conventional approaches, using simulation models for the magnetic relaxation dynamics of nanoparticle systems, i.e. a phenomenological Ising-type approach, on two levels, and a stochastic approach. The paper also shows a way of using these approaches in creating a model to simulate the Néel magnetic relaxation time for aligned magnetic nanoparticle systems.
4
Content available remote

Low Temperature Overheating Effect in SiGe p-Type Quantum Wells. Methods of the Hole-Phonon Energy Relaxation Time Determination

80%
Berkutov I.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
228-230
EN
The temperature dependence of the hole-phonon energy relaxation time τ_{hph} (T) under hot-hole conditions was studied in SiGe p-type quantum wells. The hot-hole temperature T_{h} was estimated through three different experimental methods: (i) from a comparison of the amplitude of the Shubnikov-de Haas oscillations changed by current and temperature; (ii) from a comparison of the phase relaxation time in the effect of weak localization obtained either at different temperatures and minimum current or at different current at a fixed temperature; (iii) from a comparison of the temperature and current dependences of the sample resistance. The values of T_{h} obtained by all three different methods were used to calculate, from the heat balance equation, the temperature dependence of the hole-phonon energy relaxation time τ_{hph} (T). All three temperature dependences τ_{hph} (T) were almost identical and demonstrated transition of the 2D system from "partial inelasticity" to small angle scattering at lower temperatures.
5
Content available remote

Quantum Kinetic Theory of the '2k_{F}' Scattering Mechanism for Three-Dimensional Structurally Disordered Systems in the Ioffe-Regel limit

80%
Spisak B., Wołoszyn M.
Acta Physica Polonica A
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2015
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vol. 128
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issue 2
213-215
EN
Effect of the coherent backscattering of the conduction electrons in three-dimensional structurally disordered metals specified by the Ioffe-Regel criterion is considered within the framework of the Morgan-Howson-Šaub theory of localisation which is based on the generalised kinetic equation for the Wigner distribution function and effective medium approximation. A formula for the electrical resistivity including the weak localisation correction is expressed in terms of the dimensionless transport parameter k_{F}l. The asymptotic form of the formula is derived and discussed in the context of the diagrammatic approach.
6
Content available remote

Weak Antilocalization in Quantum Wells

80%
Knap W., Skierbiszewski C., Litwin-Staszewska E., Kobbi F., Zduniak A., Robert J., Pikus G., Iordanskii S., Mosser V., Zekentes K.
Acta Physica Polonica A
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1995
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vol. 87
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issue 2
427-432
EN
Spin relaxation in degenerated two-dimensional (2D) electron gas is studied by measurements of the magnetic field dependence of the weak an­tilocalization corrections to the conductivity in GaInAs quantum wells. Con­sistent quantitative (up to order of magnitude) description of weak antilocal­ization data on GaAs like heterojunctions and quantum wells was obtained. Our results show that spin precession around the effective magnetic field direction as described by the Dyakonov-Perel model is the main spin relax­ation mechanism in degenerated 2D electron gas in semiconductors with no inversion symmetry.
7
Content available remote

Metal-Dielectric Transition in Hydrogen

80%
Shvets V., Vlasenko A.
Acta Physica Polonica A
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2008
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vol. 114
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issue 4
851-858
EN
The electrical resistivity of liquid metallic hydrogen at a temperature of 3000 K and a density of 0.35 mol/cm^3 is calculated. Hydrogen is considered as a three-component system consisting of electrons, protons, and neutral hydrogen atoms. The second order of perturbation theory in electron-proton and electron-atom interactions is used to determine the inverse relaxation time for electric conductivity. The Coulomb electron-electron interaction is taken into account in the random phase approximation and the exchange interaction and correlation of conductivity electrons are included in the local-field approximation. The model of hard spheres is used for the proton and atomic subsystems. The concentration of the electrically neutral atomic component proved to be significantly lower than the value assumed by the discoverers of metallic hydrogen.
8
Content available remote

Tight-Binding Approach: A Quantum Mechanical Tool to Study Economic Time Series

80%
Cruz H.
Acta Physica Polonica A
|
2018
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vol. 133
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issue 6
1347-1350
EN
We study the localization properties of the 1D tight-binding equation, where the on-site potential is aperiodic or pseudorandom. The on-site potential values are derived from economic time series databases. We carry out numerical work involving direct diagonalization to study localization properties of the system. In our model, eigenstates at the band center are all extended whereas the band-edge states are all localized. This diagonalization scheme is applied to different segments of the time series. The Lyapunov exponent behaves at E=0 as γ(E)~|E|^{β}. The results lead us to conclude that this mathematical tool could be used as a moving indicator to study economic charts.
9
Content available remote

Transient Response of Electrons and Phonons in ZnTe Crystals

80%
Brazis R., Raguotis R.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
933-936
EN
The response of electron and phonon ensemble to the switching on and off electric field E in n-type ZnTe crystals is simulated by Monte Carlo method. The results at T=10 K show significant accumulation of LO-phonons and the LO phonon band population inversion with respect to the LA band;the inversion is necessary for the stimulated transfer of LO-LA energy difference to photons. The maximum inversion is at E=7 kV/cm. At T=300 K no phonon band inversion but fast (sub-picosecond) drift velocity switching with ≈100 GHz repetition is feasible.
10
Content available remote

Relaxation Times in Magnetic Nanoparticles System and Memory Effects

80%
Osaci M., Abrudean C., Berdie A.
Acta Physica Polonica A
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2007
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vol. 112
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issue 6
1203-1212
EN
Some memory effects in nanoparticle systems, similar to those seen in spin glass systems, may have important device applications, by tuning the interaction and the particle size. Recently, this subject provoked a special interest in nano-sciences. In this work we present a study, by simulation of the mode in which the behavior of a magnetic nanoparticle system is influenced by the superposition of the dimensions' distribution, the effective anisotropy constants and the disposal of nanoparticles in the sample, if we take into account the dipolar magnetic interaction.
11
Content available remote

Longitudinal Magnetoresistance of Metals Calculated οn the Basis of a Single-Band Electron Theory

80%
Olszewski S.
|
EN
The longitudinal magnetoresistance of metals at different temperatures and strengths of the external magnetic field is examined with the aid of a simple single-band theory. The calculated data are compared with the experimental ones. The theoretical ratio between the longitudinal and transversal magnetoresistance approaches unity, whereas the observed ratio is rather below that value. For some metals (Al,Pt) the theoretical results are within the range of the measured data for the transversal and longitudinal resistance, or remain close to the limits of this empirical interval. In average, a relatively good agreement between experiment and theory is obtained for Al, Pt, Cu, Ag and In metals.
12
Content available remote

The Internal Friction and the Relaxation Time Spectrum of Ferroelectric Ceramic PZT Type

80%
Bartkowska J., Ilczuk J.
Acta Physica Polonica A
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2008
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vol. 114
|
issue 6A
A-7-A-13
EN
The fractional Zener model with two spring-pots is proposed to description of relaxation time spectrum of ferroelectric ceramic material. This model is based on fractional calculus. The influence of values of a and b parameters on the shape of the relaxation time spectrum was investigated.
13
Publication available in full text mode
Content available

Transport Relaxation Time of Spin-Polarized Electrons

70%
Paja A., Spisak B.
Acta Physica Polonica A
|
2004
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vol. 106
|
issue 1
69-76
EN
We study the mechanism of spin relaxation in 3D disordered metallic systems due to the spin-orbit scattering on charged impurities. The transport relaxation time for spin-polarized conduction electrons is calculated analytically in the presented model, where the screened Coulomb potential is used for the description of impurities.
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