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Wyświetlanie 1-15 z 37
Tytuł:
Monte Carlo Treatment of Non-Equilibrium Processes in n-Type InSb Crystals
Autorzy:
Ašmontas, S.
Raguotis, R.
Powiązania:
https://bibliotekanauki.pl/articles/1813219.pdf
Data publikacji:
2008-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
52.65.Pp
72.10.-d
72.10.Fk
72.20.Dp
Opis:
Numerical calculation by Monte Carlo method of the dynamic behaviour of electron ensemble in n-type InSb crystals after step-like application of electric field is presented. The results show essential influence of electron density on the energy relaxation time. The effect of electron energy cooling below equilibrium temperature in compensated n-InSb is obtained numerically for the first time, which is in agreement with experimental results.
Źródło:
Acta Physica Polonica A; 2008, 113, 3; 929-932
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Universal Relations in the Attractive Hubbard Model with Next-Nearest Neighbor Hopping
Autorzy:
Bak, M.
Powiązania:
https://bibliotekanauki.pl/articles/2046748.pdf
Data publikacji:
2006-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.25.Fy
71.10.Fd
74.20.Fg
71.27.+a
72.10.-d
Opis:
Recently a new universal relation between superfluid densityρ$\text{}_{s}$ andσ$\text{}_{dc}$T$\text{}_{c}$, where σ$\text{}_{dc}$ is direct current conductivity and T$\text{}_{c}$ - superconducting critical temperature, was found by Homes et al. (Nature 430, 539 (2004)). The theoretical derivation of the relation based on BCS theory is correct only qualitatively. In the present paper this relation is calculated theoretically, using Hartree-Fock approximation and second-order perturbation theory. It is found that although correct qualitatively, quantitatively the results are too small. Inclusion of the second neighbor hopping improves the results.
Źródło:
Acta Physica Polonica A; 2006, 109, 4-5; 565-568
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electronic Structure and Electron-Transport Properties of (Gd$\text{}_{1-x}$Y$\text{}_{x}$)$\text{}_{2}$In Compounds
Autorzy:
Borgieł, W.
Deniszczyk, J.
Powiązania:
https://bibliotekanauki.pl/articles/2013400.pdf
Data publikacji:
2000-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.10.-d
72.15.-v
71.20.Eh
71.20.-b
Opis:
Based on the electronic structure of the ferromagnetic Gd$\text{}_{2}$In and (Gd$\text{}_{0.5}$ Y$\text{}_{0.5}$)$\text{}_{2}$In compounds the high-temperature magnetic part of the electrical resistivity of (Gd$\text{}_{1-x}$Y$\text{}_{x}$)$\text{}_{2}$In as a function of Y concentration was calculated and analyzed. The main interaction which causes the finite magnetic part of the conductivity was assumed in a form of stochastically distributed in space s-f interaction. The calculated resistivity of (Gd$\text{}_{1-x}$Y$\text{}_{x}$)$\text{}_{2}$In alloys qualitatively reproduces the experimental data.
Źródło:
Acta Physica Polonica A; 2000, 97, 5; 783-786
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Resistivity of (Gd$\text{}_{1-x}$Y$\text{}_{x}$)$\text{}_{2}$In Alloys at High Temperatures - Two-Band Model Approach
Autorzy:
Borgieł, W.
Deniszczyk, J.
Lipowczan, M.
Braun, J.
Powiązania:
https://bibliotekanauki.pl/articles/2014412.pdf
Data publikacji:
2000-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.20.Eh
71.20.-b
72.15.-v
72.10.-d
Opis:
Two-band model for the substitutionary binary alloy of different rare earth metals with relatively simple 4f multiplet structure placed within the transition metal host matrix was proposed and applied to (Gd$\text{}_{1-x}$Y$\text{}_{x}$)$\text{}_{2}$In. The main interaction which causes the magnetic part of the resistivity was assumed in a form of stochastically distributed in space s-f interaction. The calculated high temperature spin disorder resistivity of (Gd$\text{}_{1-x}$Y$\text{}_{x}$)$\text{}_{2}$In alloys reproduces well the experimental alloys data.
Źródło:
Acta Physica Polonica A; 2000, 98, 5; 547-550
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Monte Carlo Studies of Quantum Cascade Lasers
Autorzy:
Borowik, P.
Thobel, J.
Bugajski, M.
Adamowicz, L.
Powiązania:
https://bibliotekanauki.pl/articles/1807675.pdf
Data publikacji:
2009-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.10.-d
72.20.Jv
73.63.-b
78.67.-n
Opis:
Results of multi particle Monte Carlo studies of a mid-infrared QCL structure, for the first time fabricated by Page et al., are presented. It has been demonstrated that for the considered structure design at least 9 electron energy levels per laser segment should be used to correctly describe the electric current properties. Mechanisms responsible for electron population on higher laser level are discussed.
Źródło:
Acta Physica Polonica A; 2009, 116, S; S-49-S-51
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Influence of Phonon Emission on Electron Transport in Hexagonal and Cubic Gallium Nitride
Autorzy:
Brazis, R.
Raguotis, R.
Powiązania:
https://bibliotekanauki.pl/articles/2041763.pdf
Data publikacji:
2005-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.10.-d
72.20.Ht
72.80.Ey
Opis:
Electron transport characteristics of GaN crystals in high electric fields are shown to be essentially influenced by different optical phonon modes inherent to the hexagonal and cubic phases of these compound crystals. Additional optical phonon modes (≈26 meV) competing with the higher-energy ones (≈92 meV) in hexagonal GaN, together with the low-lying satellite valley (Γ$\text{}_{3}$), dramatically reduce the drift mobility of electrons in comparison with conventional models. Presented Monte Carlo data are in excellent agreement with the time-of-flight experiment. The cubic GaN crystal phase with its satellite electron energy valleys shifted well above the main (Γ$\text{}_{1}$) valley is chosen as a convenient medium for elucidating the role of high-energy longitudinal optical phonon accumulation. A simple efficient one-particle Monte Carlo method is proposed for an account of excess phonons. Phonon heating is shown to bring about the moderate additional reduction of the drift mobility and an increase in mean electron energy.
Źródło:
Acta Physica Polonica A; 2005, 107, 2; 324-327
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Quantum Cascade Laser Design for Tunable Output at Characteristic Wavelengths in the Mid-Infrared Spectral Range
Autorzy:
Daničić, A.
Radovanović, J.
Milanović, V.
Indjin, D.
Ikonić, Z.
Powiązania:
https://bibliotekanauki.pl/articles/1537879.pdf
Data publikacji:
2010-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.10.-d
73.21.Fg
Opis:
We present a method for systematic optimization of quantum cascade laser active region, based on the use of the genetic algorithm. The method aims at obtaining a gain-maximized structure, designed to emit radiation at specified wavelengths suitable for direct absorption by pollutant gasses present in the ambient air. After the initial optimization stage, we introduce a strong external magnetic field to tune the laser output properties and to slightly modify the emission wavelength to match the absorption lines of additional compounds. The magnetic field is applied perpendicularly to the epitaxial layers, thus causing two-dimensional continuous energy subbands to split into series of discrete Landau levels. This affects all the relevant relaxation processes in the structure and consequently the lifetime of carriers in the upper laser level. Furthermore, strong effects of band nonparabolicity result in subtle changes of the lasing wavelength at magnetic fields which maximize the gain, thus providing a path for fine-tuning of the output radiation properties. Numerical results are presented for GaAs/$Al_{x}Ga_{1-x}As$ based quantum cascade laser structures designed to emit at particular wavelengths in the mid-infrared part of the spectrum.
Źródło:
Acta Physica Polonica A; 2010, 117, 5; 772-776
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Valence Band of Cubic Semiconductors from Viewpoint of Clifford Algebra
Autorzy:
Dargys, A.
Powiązania:
https://bibliotekanauki.pl/articles/1807789.pdf
Data publikacji:
2009-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.15.-m
72.25.Dc
75.10.Jm
85.75.-d
Opis:
In this paper the properties of semiconductors having cubic symmetry are considered in a real multidimensional Euclidean space within the formalism of multivector Clifford algebra rather than, usually used for this purpose, complex Hilbert space. In particular, it is demonstrated how the valence band energy spectrum and spin properties may be calculated within $Cl_5$ Clifford algebra and SO(5) symmetry group related with it.
Źródło:
Acta Physica Polonica A; 2009, 116, 2; 226-231
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Mechanism of Carrier Heating in High Electric Field Electroluminescence Devices
Autorzy:
Dedulewicz, S.
Godlewski, M.
Powiązania:
https://bibliotekanauki.pl/articles/1924197.pdf
Data publikacji:
1992-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.10.-d
78.60.Fi
Opis:
The mechanism of carrier heating in ZnS-based electroluminescence devices is discussed. We show that carrier acceleration by an applied electric field is at 300 K not a loss-free (ballistic carriers) process. Even for large carrier energies (about 2.5 eV) inelastic scattering on polar optical phonons dominates over elastic scattering on acoustic phonons and ionized impurities.
Źródło:
Acta Physica Polonica A; 1992, 82, 5; 865-867
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Band Structure and Magnetic Properties of DO$\text{}_{3}$-Type Fe$\text{}_{3-x}$V$\text{}_{x}$Al Alloys. Super-Cell Approach
Autorzy:
Deniszczyk, J.
Borgieł, W.
Powiązania:
https://bibliotekanauki.pl/articles/2014414.pdf
Data publikacji:
2000-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.20.Eh
71.20.-b
72.15.-v
72.10.-d
Opis:
The electronic structure of Fe$\text{}_{3-x}$V$\text{}_{x}$Al alloys was calculated using the super-cell methodology of alloy modeling. The concentration range of x=0.0÷1.0 was investigated. For a concentration of x=0.0625 the energy based analysis reveals that vanadium prefers to replace the Fe atom at sites with the octahedral coordination. It was found that the iron atoms coordinated by the eight nearest-neighbor Fe atoms preserve their high magnetic moment up to a concentration of x=0.9375 even though the average total magnetic moment goes to zero. The relatively high (≃ -1.0μB) negative magnetic moment of V remains constant up to x≃ 0.5. In the concentration range of x=0.75÷0.9375 the gap at ε$\text{}_{F}$ of the minority density of states is observed while the majority density of states displays a sharp peak structure at the Fermi energy. This feature suggests the heavy-fermion behavior of the Fe$\text{}_{2}$VAl compound.
Źródło:
Acta Physica Polonica A; 2000, 98, 5; 551-554
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Low-Dimensional Thermoelectricity
Autorzy:
Heremans, J. P.
Powiązania:
https://bibliotekanauki.pl/articles/2043708.pdf
Data publikacji:
2005-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.10.-d
73.63.-b
81.07.-b
Opis:
Thermoelectric materials are used as solid-state heat pumps and as power generators. The low efficiency of devices based on conventional bulk thermoelectric materials confines their applications to niches in which their advantages in compactness and controllability outweigh that drawback. Recent developments in nanotechnologies have led to the development of thermoelectric nano-materials with double the efficiency of the best bulk materials, opening several new classes of applications for thermoelectric energy conversion technology. We review here first the physical mechanisms that result in the superior thermoelectric performance of low-dimensional solids, compared to bulk thermoelectric materials: they are a reduction of the lattice thermal conductivity, and an increase in the Seebeck coefficient S for a given carrier density. The second part of this review summarizes experimental results obtained on macroscopic arrays of bismuth, antimony, and zinc nanowires with diameters ranging from 200 to 7 nm. We show how size-quantization effects greatly increase S for a given carrier concentration, as long as the diameter of the nanowires remains above 9 nm, below which localization effects start dominating. In a third part, we give data on PbTe nanocomposites, particularly bulk samples containing 30~nm diameter Pb inclusions. These inclusions affect the electron scattering in such a way as to again increase the Seebeck coefficient.
Źródło:
Acta Physica Polonica A; 2005, 108, 4; 609-634
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Influence of Chemical Composition of Liquid Phase and Growth Process on Physical Properties of $Bi_2Se_3,$ $Bi_2Te_3$ and $Bi_2Te_2Se$ Compounds
Autorzy:
Hruban, A.
Materna, A.
Dalecki, W.
Strzelecka, G.
Piersa, M.
Jurkiewicz-Wegner, E.
Diduszko, R.
Romaniec, M.
Orłowski, W.
Powiązania:
https://bibliotekanauki.pl/articles/1492965.pdf
Data publikacji:
2011-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.55.-i
72.10.-d
72.15.-v
72.20.-I
73.20.-r
Opis:
We studied synthesis and crystal growth of $Bi_2Te_3,$ $Bi_2Se_3$ and $Bi_2Te_2Se$ compounds by means of vertical Bridgman method. Crystals were grown from stoichiometric melts and under different molar ratio of Bi:Te, Bi:Se or Bi:Te:Se. The obtained crystals were characterized by X-ray diffraction analysis, energy dispersive X-ray spectroscopy, scanning electron microscopy, atomic force microscopy, and the Hall effect measurements. Some of the samples demonstrated insulating bulk behavior, by means of resistivity versus temperature measurements.
Źródło:
Acta Physica Polonica A; 2011, 120, 5; 950-953
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Angular Distribution of Photoemission from Surfaces of Amorphous Solids
Autorzy:
Jabłoński, A.
Powiązania:
https://bibliotekanauki.pl/articles/1931731.pdf
Data publikacji:
1994-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
34.80.Bm
72.10.-d
79.60.-i
Opis:
As follows from the formalism of X-ray photoelectron spectroscopy, knowledge of the angular distribution of photoemission is crucial for certain applications of quantitative X-ray photoelectron spectroscopy analysis. In the present work, the experimental data on the relative angular distribution of photoemission from solid materials are reviewed and compared with theoretical predictions. Noticeable discrepancies are usually observed. It has been proved that major part of the observed discrepancies can be ascribed to elastic photoelectron scattering. The commonly used formalism, where the elastic collisions are neglected, may be of insufficient reliability for certain solids, or in certain experimental geometries. This formalism can be easily extended to account for elastic photoelectron collisions by introducing two correction factors, Q$\text{}_{X}$ and β$\text{}_{eff}$. The second parameter, called the effective asymmetry parameter, describes the observed decrease in anisotropy of photoemission. Determination of the correction factors requires a reliable theory describing elastic electron scattering in the solid. A need arises for accurate differential and total elastic electron scattering cross-sections pertinent to kinetic energies of considered photoelectrons or the Auger electrons. The increasingly important role of electron transport in surface analysis has stimulated an effort to construct a complete database containing the differential and total atomic elastic scattering cross-sections.
Źródło:
Acta Physica Polonica A; 1994, 86, 5; 787-798
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Point-Contact Spectroscopy
Autorzy:
Jansen, A. G. M.
Powiązania:
https://bibliotekanauki.pl/articles/1920956.pdf
Data publikacji:
1992-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.10.-d
73.40.Jn
Opis:
In a small metallic constriction ("point contact") the transport of electrons is ballistic. The applied voltage V tunes a well-defined non-equilibrium energy eV of electrons. The nonlinear current-voltage characteristics can be used to perform energy-resolved spectroscopy of the inelastic scattering of electrons with elementary excitations in metal (e.g. phonons, magnons, crystal-field levels, paramagnetic impurities). The basic elements of the point--contact method and its applications will be discussed. In recent point-contact experiments the observed phenomena (weak localization, resistance fluctuations) need a description that goes beyond the classical Boltzmann approach of electronic transport in a point contact. In analogy to observed effects in the diffusive transport in mesoscopic systems, these phenomena are explained by considering quantum-interference effects in the ballistic transport near the contact region related to the wave character of the electrons.
Źródło:
Acta Physica Polonica A; 1992, 82, 4; 539-550
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ultrafast Dynamics and Quantum Transport of Electrons in Strongly Disordered Semiconductors
Autorzy:
Kalvová, A.
Velický, B.
Powiązania:
https://bibliotekanauki.pl/articles/1933801.pdf
Data publikacji:
1995-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.25.-s
72.10.-d
78.47.+p
Opis:
The new experiments on the response of electrons in semiconductors to femtosecond optical pulses call for developing adequate theoretical tools. A promising approach has been found in using the non-equilibrium Green functions approximately factorized on the basis of the so-called generalized Kadanoff-Baym ansatz. The present work investigates the validity of such approach on an example of a semiconductor with an alloy scattering, where the coherent potential approximation allows to construct the non-equilibrium Green functions directly, so that an explicit comparison with the ansatz decoupling is possible. The ansatz for the electron distribution is in this case justified as far as the quasiparticle picture for the individual electrons is appropriate.
Źródło:
Acta Physica Polonica A; 1995, 88, 4; 767-770
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 37

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