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Wyświetlanie 1-15 z 455
Tytuł:
Optical Processes in Quantum Wells
Autorzy:
Sham, L. J.
Powiązania:
https://bibliotekanauki.pl/articles/1931845.pdf
Data publikacji:
1995-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.20.Dx
78.55.Cr
Opis:
A review is given of the theoretical framework of exciton dynamics in quantum wells including the spin degrees of freedom. A study is made of various momentum, energy, and spin relaxation mechanisms including the effects of exciton-phonon interaction, the single-particle spin-flips by means of spin-orbit interaction and the exciton spin-flip by means of the exchange interaction. All these competing mechanisms are taken into account in a set of equations governing the time evolution of the exciton spin populations. Solutions are then used to interpret observed time-resolved observations of polarized luminescence spectra. For excitons in a two-dimensional system such as a semiconductor quantum well, the breaking of the translational symmetry in the direction normal to the interface plane has been shown theoretically by Hanamura, by Andreani and Bassani, and by Citrin to result in a recombination rate much faster than in a three-dimensional system. Yet, experiments show comparable decay rates in two- and three-dimensional excitons. Recent experiments with high time resolutions show two decay times for the total luminescence intensity. The slower one agrees with the one usually observed and interpreted as the radiative recombination time. We shall give an explanation for the fast decay as a combination of radiative recombination and single-particle spin-flip and for the slow decay as the radiative recombination slowed down by the presence of lower energy dark states for excitons with parallel spins. The ability to use the same theory to account for the polarization behavior confirms the importance of the exciton spin dynamics. Furthermore, the longitudinal electric field dependence is used to check our theory of exchange.
Źródło:
Acta Physica Polonica A; 1995, 87, 1; 7-15
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin-Wave Resonance in Magnetic Semiconductor Thin Films - Experiment
Autorzy:
Maksymowicz, L. J.
Lubecka, M.
Powroźnik, W.
Powiązania:
https://bibliotekanauki.pl/articles/1891787.pdf
Data publikacji:
1991-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.60.Gx
75.70.Ak
Opis:
Magnetic properties of polycrystalline thin films of chromium chalcogenide spinels (CdCr$\text{}_{2}$Se$\text{}_{4}$ lightly doped with indium and CdCr$\text{}_{2x}$In$\text{}_{2-2x}$Se$\text{}_{4}$) were studied. The ferromagnetic (FMR) and spin-wave resonance (SWR) techniques were used to investigate the temperature dependences of both the spin-wave stiffness constant D and the saturation magnetization M$\text{}_{s}$. The resonance spectra were recorded in the temperature range extending from 4.2 K to 300 K. The influence of indium concentration on M$\text{}_{s}$(T) and D(T) was studied. It was shown that lightly doped samples (In/Cd < 1% at.) exhibited the ferromagnetic ordering with M$\text{}_{s}$(T) and D(T) being the linear functions of T$\text{}^{3}$ $\text{}^{/}$ $\text{}^{2}$ and T$\text{}^{5}$ $\text{}^{/}$ $\text{}^{2}$, respectively. Higher concentration of indium produced the reentrant transition and spin-glass state of magnetic ordering in CdCr$\text{}_{2x}$In$\text{}_{2-2x}$Se$\text{}_{4}$. The temperature dependence of M$\text{}_{s}$ was also found from the FMR data for these two magnetic phases.
Źródło:
Acta Physica Polonica A; 1991, 80, 5; 653-664
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
H-T Phase Diagram of Magnetic Semiconductor Thin Films - Experiment
Autorzy:
Lubecka, M.
Maksymowicz, L. J.
Szymczak, R.
Powroźnik, W.
Powiązania:
https://bibliotekanauki.pl/articles/1964793.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Gw
75.50.Lk
64.60.Cn
Opis:
We used the irreversibilities between the field cooled and zero field cooled dc magnetization to determine the field and composition dependence of the spin-glass freezing temperature in CdCr$\text{}_{2}$Se$\text{}_{4}$ : In (REE) and CdCr$\text{}_{2-2x}$In$\text{}_{2x}$Se$\text{}_{4}$ (0.15 ≤ x ≤ 0.35) (SG) thin films. The H-T phase diagram of samples with REE has two instability lines: the Gabay-Toulouse-type (G-T) and the De Almeida-Thouless-type (A-T) while samples in SG state are characterized by the A-T line. The A-T line of thin films was used for calculation the normalised internal magnetic field h$\text{}_{m}$ of infinite spin clusters with long range ordering.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 433-436
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Thin Films Investigations by Means of Spin-Wave Resonance
Autorzy:
Maksymowicz, A. Z.
Maksymowicz, L. J.
Whiting, J. S. S.
Powiązania:
https://bibliotekanauki.pl/articles/1891792.pdf
Data publikacji:
1991-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
76.50.+g
76.30.-v
73.90.+f
Opis:
Magnetic resonance technique may successfully be applied to determine some basic parameters such as g-factor, magnetization M$\text{}_{s}$ or anisotropy energy constant K$\text{}_{u}$ in thin magnetic films. These parameters are obtained from a ferromagnetic resonance experiment when uniform precession of M$\text{}_{s}$ takes place. From spin-wave resonance one may extract very valuable information on the exchange constant A or the surface conditions characterized by the surface anisotropy energy (or pinning parameters ρ). In fact, it is only spin-wave resonance or similar techniques which allow for measurements of A, ρ or the coupling constant K$\text{}_{c}$ between ferromagnetic sublayers in multi-layered structure. The magnetic phase diagram, temperature dependence of the spin-waves stiffness constant, and the anisotropy energy constant may also be listed as less common examples of spin-wave resonance technique application for the investigation of thin films. This paper presents a theoretical approach to typical examples of experimental results and their interpretation from spin-wave resonance measurements.
Źródło:
Acta Physica Polonica A; 1991, 80, 5; 665-673
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Semiconductor Materials for Ultrafast Photoswitches
Autorzy:
Coutaz, J.-L
Powiązania:
https://bibliotekanauki.pl/articles/2035566.pdf
Data publikacji:
2002
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
85.60.-q
85.60.Dw
72.20.-i
72.40.+w
72.80.Ey
42.65.Re
Opis:
This paper gives a review of semiconductor materials that are used to fabricate ultrafast photoswitches. The optoelectrical response of the switches is first described with simple models, from which the material requirements are deduced. The basic principles of the required material properties - ultrashort free carrier lifetime and high mobility, high dark resistivity, and high field breakdown - are explained. Then, the most popular ultrafast semiconductors are listed, together with their characteristics. A special emphasis is put on low-temperature grown GaAs. Finally, two applications of these ultrafast materials are presented, namely antennae for terahertz radiation and all-optical nonlinear devices.
Źródło:
Acta Physica Polonica A; 2002, 102, 4-5; 495-512
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Singular Pretransitional Behavior of the Electric Field-Dependent Part of the Thermodynamic Quantities of Strongly Polar Mesogenic Liquids in the Isotropic Phase
Autorzy:
Jadżyn, J.
Déjardin, J.-L.
Czechowski, G.
Powiązania:
https://bibliotekanauki.pl/articles/2047352.pdf
Data publikacji:
2007-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.70.Md
65.40.Gr
77.22.Ch
Opis:
A new interpretation of the pretransitional temperature behavior of the static dielectric permittivity and its derivative in terms of the basic thermodynamic quantities: the internal energy, the entropy, and the Helmholtz free energy is presented. It was shown that in the case of strongly polar mesogenic compounds (as the homologous series of alkylcyanobiphenyls) the electric field-induced increments of both the internal energy and the entropy exhibit a critical-like temperature dependence in the vicinity of transition from the isotropic liquid to the nematic phase. As a most important pretransitional effect, it is shown that at a temperature of about 10 degrees before the phase transition, an electric field applied to the isotropic liquids induces an increase in the entropy (Δ S>0) instead of its decrease, as observed far from the phase transition or for the non-mesogenic dipolar liquids.
Źródło:
Acta Physica Polonica A; 2007, 111, 6; 877-884
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Tunnelling of Direct and Indirect Excitons in Slightly Asymmetric Double Quantum Wells
Autorzy:
Mazurenko, D. A.
Akimov, A. V.
Moskalenko, E. S.
Zhmodikov, A. L.
Kaplyanskii, A. A.
Challis, L. J.
Cheng, T. S.
Foxon, C. T.
Powiązania:
https://bibliotekanauki.pl/articles/1952066.pdf
Data publikacji:
1996-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.20.Dx
63.20.Kr
Opis:
We report the first studies of luminescence spectra from asymmetric double quantum wells of GaAs with widths around 100 Å differing by only one (2.8 Å) or two monolayers. Studies of the position and intensity of the direct and indirect exciton lines suggest the existence of acoustic phonon-assisted tunnelling between exciton states separated by a few meV. At temperatures 10-20 K the electron tunnelling process is fast enough to maintain thermal equilibrium between these direct and indirect excitons which are connected with holes in the same quantum well.
Źródło:
Acta Physica Polonica A; 1996, 90, 5; 895-898
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Dielectric Relaxation in Hydrogen Bonded Urea-Based Supramolecular Polymer N,N-di(2,2-dipentylheptyl)urea
Autorzy:
Jadżyn, J.
Bouteiller, L.
Déjardin, J.-L.
Czechowski, G.
Powiązania:
https://bibliotekanauki.pl/articles/2047092.pdf
Data publikacji:
2006-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.82.Pv
77.22.Gm
81.16.Fg
82.30.Rs
Opis:
Results of the dielectric relaxation studies, performed for supramolecular polymer formed by N,N'-di(2,2-dipentylheptyl)urea dissolved in carbon tetrachloride, are presented. The measurements were done for N,N'-di(2,2-dipentylheptyl)urea concentration up to about 7% (in mole fraction) in the frequency region from 100 kHz to 100 MHz and at the temperatures from 5ºC to 50ºC. The analysis of the experimental data were performed with the Havriliak-Negami equation. In the studied range of N,N'-di(2,2-dipentylheptyl)urea concentration and temperature, the obtained values of exponentsα andβ of the Havriliak-Negami equation are equal to 0.9±0.1 and 0.7±0.1, respectively, showing an anomaly in the dielectric relaxation behavior close to the Davidson-Cole type. Two examples of the modeling of dielectric properties of the supramolecular polymer solutions were presented.
Źródło:
Acta Physica Polonica A; 2006, 110, 4; 495-504
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Susceptibility of Sn$\text{}_{1-x}$Au$\text{}_{x}$Te
Autorzy:
Górska, M.
Anderson, J. R.
Peng, J. L.
Gołacki, Z.
Powiązania:
https://bibliotekanauki.pl/articles/1929705.pdf
Data publikacji:
1993-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.20.Ck
75.30.Et
Opis:
The magnetic susceptibility of Bridgman-grown Sn$\text{}_{1-x}$Eu$\text{}_{x}$Te with nominal values of x up to 0.095 was measured over a temperature range from 2 to 385 K. The samples were p-type with hole concentrations up to 1.5 × 10$\text{}^{21}$ cm$\text{}^{-3}$. The susceptibility data above 50 K followed the Curie-Weiss relation with a small Curie temperature. At about 10 K a small cusp in susceptibility was observed in samples with the higher range of x values. The data indicate a presence of both antiferromagnetic and ferromagnetic exchange interactions, with some paramagnetic contributions from charged defects. There is also evidence of Eu going into the lattice both as Eu$\text{}^{2+}$ and Eu$\text{}^{3+}$ ions.
Źródło:
Acta Physica Polonica A; 1993, 84, 4; 665-668
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Anomalous Dielectric Relaxation in Binary Mixtures of Mesogenic Solvent/Non-Mesogenic Solute
Autorzy:
Jadżyn, J.
Bauman, D.
Déjardin, J. -L.
Ginovska, M.
Czechowski, G.
Powiązania:
https://bibliotekanauki.pl/articles/2043683.pdf
Data publikacji:
2005-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.30.Eb
64.70.Md
87.15.Nn
68.35.Rh
83.10.Mj
Opis:
Dielectric relaxation studies for mixtures of strongly polar and mesogenic n-heptylcyanobiphenyl with non-polar and non-mesogenic carbon tetrachloride (CCl$\text{}_{4}$) were performed. The absorption band broadening due to fractional diffusion was observed. A correlation between the non-mesogenic admixture concentration and the anomalous diffusion exponent was found.
Źródło:
Acta Physica Polonica A; 2005, 108, 3; 479-489
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Neutron Diffraction Studies of MnFeAs$\text{}_{y}$P$\text{}_{1-y}$ System
Autorzy:
Zach, R.
Bacmann, M.
Fruchart, D.
Soubeyroux, J. L.
Nizioł, S.
Fruchart, R.
Powiązania:
https://bibliotekanauki.pl/articles/1861313.pdf
Data publikacji:
1994-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.-m
75.25.+z
Opis:
Magnetic structures of the MnFeAs$\text{}_{y}$P$\text{}_{1-y}$ system were examined by means of the neutron diffraction technique in the 1.5-300 K temperature range. Atomic ordering in the metal sublattices, temperature dependence of the incommensurate (y = 0.2 and y = 0.275) and of the ferromagnetic (y = 0.275, y = 0.3, y = 0.5) ordering is discussed.
Źródło:
Acta Physica Polonica A; 1994, 85, 1; 229-231
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Optical Detection of Cyclotron Resonance in Serpentine Superlattice Quantum-Wire Arrays
Autorzy:
Świątek, K.
Weman, H.
Miller, M. S.
Petroff, P. M.
Merz, J. L.
Powiązania:
https://bibliotekanauki.pl/articles/1929679.pdf
Data publikacji:
1993-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.66.Fd
76.40.+b
71.25.Jd
Opis:
We report low-temperature studies of microwave-induced cyclotron resonance of photo-generated carriers in (Al,Ga)As serpentine superlattice quantum-wire arrays. The geometric size of the parabolic-crescent cross-section of the quantum wires was of the order of 100 Å × 50 Å, depending on the angle of the vicinal substrate and the amount of parabolic curvature. Comparing the obtained spectra, we estimate the relative degree of carrier confinement in the ordered AlGaAs structure.
Źródło:
Acta Physica Polonica A; 1993, 84, 3; 583-586
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electron Energy Spectra from the Strong-Field Double-Ionization of Xenon
Autorzy:
Chaloupka, J. L.
Lafon, R.
Rudati, J.
Sheehy, B.
Agostini, P.
Kulander, K. C.
DiMauro, L. F.
Powiązania:
https://bibliotekanauki.pl/articles/2030465.pdf
Data publikacji:
2002-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
32.80.Fb
31.90.+s
32.80.Rm
Opis:
The electron energy spectra correlated to the strong-field double-ionization of xenon are presented at three laser intensities. The double-ionization electrons are on average more energetic than those generated from single-ionization. This difference in energy is not manifested as a simple scaling to higher electron energies, but rather as a change in the shape of the spectra. This trend is observed at all intensities. Most notably, the comparison between single- and double-ionization spectra is very similar at low and high peak laser intensities. This could imply that a sequential double-ionization process dominates at all intensities, even where the double ion yield is enhanced.
Źródło:
Acta Physica Polonica A; 2002, 101, 3; 337-346
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theoretical and Experimental Study of the Radiative Decay Process in a Modulation Doped GaAs/AlGaAs Heterointerface
Autorzy:
Lundström, T.
Bergman, J. P.
Holtz, P. O.
Monemar, B.
Campman, K.
Merz, J. L.
Gossard, A. C.
Powiązania:
https://bibliotekanauki.pl/articles/1968124.pdf
Data publikacji:
1997-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.66.-w
78.60.-b
Opis:
We have theoretically and experimentally investigated the radiative recombination process in an n-type modulation doped GaAs/Al$\text{}_{0.35}$Ga$\text{}_{0.65}$As heterostructure. The dynamical reshaping of the potential profile across the heterojunction, and the decay of the spatially indirect radiative recombination between electrons in the two-dimensional electron gas and photo-created holes, have been numerically simulated for various values of the electric field across the heterojunction. Optical matrix elements were deduced from a self-consistent solution of the coupled Schrodinger and Poisson equations at every discrete point of time. The calculated recombination energies and integrated luminescence intensities were compared with experimental data from time-resolved photoluminescence measurements on an 800 Å wide GaAs/AlGaAs heterostructure.
Źródło:
Acta Physica Polonica A; 1997, 92, 4; 824-828
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Near Field Optical Microscopy and Spectroscopy with STM and AFM Probes
Autorzy:
Bergossi, O.
Bachelot, R.
Wioland, H.
Wurtz, G.
Laddada, R.
Adam, P. M.
Bijeon, J. L.
Royer, P.
Powiązania:
https://bibliotekanauki.pl/articles/1968764.pdf
Data publikacji:
1998-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
07.60.Pb
42.62.Fi
61.16.Ch
68.35.Bs
Opis:
This article deals with a new generation of scanning near field optical microscopes (SNOM), called apertureless SNOM, based on metallic, semi-conductive or dielectric probes. The classification of the apertureless probe among the usual SNOM probes is discussed in the first part. Then, we present the different apertureless SNOM configurations that we develop, with various commercial AFM and home-made tungsten tips, and several illumination and collection modes. Finally, after a preliminary result in near field imaging, we propose a promising application of such microscopes dedicated to the near field fluorescence spectroscopy.
Źródło:
Acta Physica Polonica A; 1998, 93, 2; 393-398
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 455

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