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Wyświetlanie 1-15 z 119
Tytuł:
Coupled States of the System of Two Free Electrons on a Single Star
Autorzy:
Walcerz, S.
Lulek, T.
Powiązania:
https://bibliotekanauki.pl/articles/1891910.pdf
Data publikacji:
1991-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
02.20.+b
71.45.-d
75.10.Lp
75.20.-g
Opis:
A classification scheme of quantum states for the system of two free electrons in a cubic box, confined to a single star of quasi-momentum is proposed within a Racah-Wigner type of approach. Coupling of angular momenta of the atomic case is here substituted by Mackey theorem for transitive representations, which provides a crystalline analogue of orbital angular momentum - the resultant orbit of the geometric symmetry group. The action of the Pauli group is combined with that of the octahedral group which yields the connection between spin (i.e. the singlet or triplet pairing of electrons) and statistic of the positional factor. Resultant singlets and doublets - irreducible representations of the octahedral group, exhibit an ordinary Landau diamagnetic behaviour, whereas triplets are paramagnetic. A relation between the Mackey star and the star of resultant momentum is discussed.
Źródło:
Acta Physica Polonica A; 1991, 80, 6; 781-792
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Wigner-Racah Description of the Free-Electron Model
Autorzy:
Lulek, T.
Powiązania:
https://bibliotekanauki.pl/articles/1891909.pdf
Data publikacji:
1991-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
02.20.+b
71.45.-d
75.10.Lp
75.20.-g
Opis:
A version of Wigner-Racah type of approach is proposed for the model of a free-electron gas in a cubic box. The approach bases on the structure of fibre bundle in description of states of a single electron. Contrary to the tight binding model, the base of the bundle is the reciprocal space rather than the positional one. An elementary quantity of the approach is the star of quasi-momentum. Such a treatment reveals the degeneracy of energy levels of the system of N electrons, in particular of the ground Fermi level, for an uncomplete filling of stars. The associated classification of energy levels and corresponding states can be performed within an atomic-like Wigner-Racah scheme.
Źródło:
Acta Physica Polonica A; 1991, 80, 6; 769-779
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Aspects of Magnetism in Heavy-Electron Metals
Autorzy:
Ott, H. R.
Powiązania:
https://bibliotekanauki.pl/articles/1860764.pdf
Data publikacji:
1994-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.20.-g
75.20.Hr
75.30.-m
75.30.Mb
Opis:
For some time it was believed that heavy-mass electrons at low temperatures, in special rare-earth and actinide compounds, were due to a particular suppression of magnetic order in these materials. Various experiments reveal, however, that magnetic order may occur from a heavy-electron state and that also a heavy-electron state may develop in the presence of a magnetically-ordered matrix. Even in materials with no sign of a cooperative phase transition, microscopic experimental probes give evidence for strong magnetic correlations, involving only very tiny (< 10^{-1} μ_{B}) ordered moments, however. All these experimental observations indicate that the heavy-electron state cannot always be regarded as a simple Fermi liquid in the usual sense. Various interactions of similar strength need to be considered. It is suggested that the balance of these interactions may lead to electronic inhomogeneities in k space. Both in magnetically-ordered or superconducting systems, unexpected electronic degrees of freedom appear to exist. In other cases experimental observations suggest magnetic inhomogeneities in real space which are not simply due to chemical inhomogeneities. Different examples of these various possibilities are demonstrated and discussed.
Źródło:
Acta Physica Polonica A; 1994, 85, 1; 7-19
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
1,1-Dithiolenes: the Good, the Not Bad, and the Ugly
Autorzy:
Cassoux, P.
Bowlas, C. J.
Lahlil, K.
Moradpour, A.
Bonvoisin, J.
Launay, J.-P
Powiązania:
https://bibliotekanauki.pl/articles/1933327.pdf
Data publikacji:
1995-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
33.20.-t
82.40.-g
82.45.+z
33.10.-n
82.30.-b
Opis:
A series of 1, 1'-dithiolate ligands were used in the attempted preparation of metal complexes. These bidentate sulphur ligands were subsequently used in aromatic nucleophilic substitution reactions giving rise to several novel organic donor molecules. The electrochemistry data of two of the donors and their subsequent use in the preparation of donor-acceptor compounds is presented. One donor-acceptor compound exhibited high room temperature conductivity (up to 900 S cm$\text{}^{-1}$) and remained metallic down to low temperature. One donor containing two tetrathiafulvalene units was studied by near infrared absorption spectroscopy. An intervalence transition in the monocation form of this donor was observed, indicating that it behaves as a class II mixed valence compound.
Źródło:
Acta Physica Polonica A; 1995, 87, 4-5; 743-748
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Diluted Magnetic Semimetals - Beyond Heisenberg Coupling
Autorzy:
Wilamowski, Z.
Story, T.
Jantsch, W.
Powiązania:
https://bibliotekanauki.pl/articles/1931949.pdf
Data publikacji:
1995-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.20.-g
75.30.Hx
76.20.+q
Opis:
We analyse effects which cannot be explained assuming the isotropic Heisenberg form of sp-d or of the indirect d-sp-d (RKKY) coupling. Resonance line broadening, a line shift and an enhancement of the magnetic anisotropy in diluted magnetic semimetals are discussed.
Źródło:
Acta Physica Polonica A; 1995, 87, 1; 189-192
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Preparation and Some Properties of Carbon Nanotubes
Autorzy:
Byszewski, P.
Ukalski, K.
Baran, M.
Dlużewski, P.
Kozłowski, M.
Powiązania:
https://bibliotekanauki.pl/articles/1933400.pdf
Data publikacji:
1995-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.20.-g
81.35.+k
Opis:
Carbon nanotubes can be grown in the DC electric arc, they grow covered by a turbostratic graphite. The mechanism of the tubes growth is discussed. The magnetic susceptibility of samples, which contained aligned nanotubes exhibits anisotropic oscillatory behavior, which is ascribed to spatial quantization of the energy levels.
Źródło:
Acta Physica Polonica A; 1995, 87, 4-5; 885-891
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Oscillations in Reflectivity of Samples with X-ray Waveguide Layers
Autorzy:
Pełka, J. B.
Lagomarsino, S.
Di Fonzo, S.
Jark, W.
Domagała, J.
Powiązania:
https://bibliotekanauki.pl/articles/1945221.pdf
Data publikacji:
1996-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
68.65.+g
78.20.Ci
Opis:
The glancing-angle reflectivity profiles in samples containing an X-ray waveguide layer are studied. Oscillations observed at angles within the region of resonance and above, are interpreted by angle dependent interference of the monochromatic X-ray beam in thin layer. The discussion is extended to the structures composed of more than one layer. Experimental reflectivity spectra recorded with Cu K$\text{}_{α}$ radiation are compared with the theoretical calculations. It leads to the model of oscillations in reflectivity consistent both for the resonant and non-resonant regions, and clarifies interpretation of oscillations in the region above the resonances. A brief discussion of potential applications of the reflectivity spectra to the studies of structure of thin layers is done.
Źródło:
Acta Physica Polonica A; 1996, 89, 3; 323-328
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Racah Recoupling Matrices for System of Two Free Electrons Confined To Single Star
Autorzy:
Lulek, T.
Kłos, J.
Powiązania:
https://bibliotekanauki.pl/articles/1945688.pdf
Data publikacji:
1996-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
02.20.-a
31.10.+z
75.10.Lp
75.20.-g
Opis:
Racah-Wigner type of calculus is adapted to the system of two free electrons in a cubic box, confined to a single star p00 of quasimomentum. Various coupling schemes (LS-like, jj-like, and transitive) have been reviewed in analogy to the case of a free atom. Racah recoupling matrices are calculated explicitly, and their quantum-mechanical meaning is exposed in terms of octahedral multipoles.
Źródło:
Acta Physica Polonica A; 1996, 90, 3; 483-490
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Partial Probabilities of X-Ray Bremsstrahlung Transitions
Autorzy:
Nietubyć, R.
Sobczak, E.
S̆imůnek, A.
Vackár̆, J.
S̆ipr, O.
Powiązania:
https://bibliotekanauki.pl/articles/1963394.pdf
Data publikacji:
1997-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
79.20.Kz
78.70.-g
Opis:
High-energy electrons bombarding a solid produce X-ray bremsstrahlung radiation, which is one of few elementary processes occurring during electron-solid interactions. Photon emission results from electron transition to an unoccupied electron state above the Fermi level. In this work matrix elements of X-ray bremsstrahlung transitions were calculated for solids containing elements from N (Z=7) to Pd (Z=46) and photon energies 1487 eV and 5415 eV. It was found that in the case of light elements the X-ray bremsstrahlung transitions to s-type final states dominate over all other symmetries. It was also shown that X-ray bremsstrahlung transition probabilities increase with decreasing photon energy and increasing atomic number Z. Dependence of X-ray bremsstrahlung transition probabilities on the electron final state energy is also presented in this work.
Źródło:
Acta Physica Polonica A; 1997, 91, 5; 841-846
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Study of Photoelectron Emission Yield from Layered Structures in Presence of Resonance-Enhanced X-Ray Propagation Effect
Autorzy:
Pełka, J. B.
Lagomarsino, S.
Cedola, A.
Di Fonzo, S.
Jark, W.
Powiązania:
https://bibliotekanauki.pl/articles/1963396.pdf
Data publikacji:
1997-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
68.65.+g
78.20.-e
Opis:
In this work we present the new experimental results of total photoelectric yield as well as energy distribution of photoelectrons excited in a thin carbon film deposited on Ni mirror in the presence of resonance-enhanced X-ray propagation effect. The measurements were performed using conventional X-ray tube as a radiation source for the energy Cu K$\text{}_{α}$ (8047 keV). The spectra were recorded using a flow proportional electron counter with energy resolution of about 15%, and multichannel pulse height analyzer. A comparison with the reflectivity spectra recorded at the same time show an excellent correlation of both kinds of spectra, consistently with the theoretical prediction. A map of electron energy distribution is reported. Although the applied electron counter was of low energetic resolution the recorded spectra show characteristic regularities and indicate that the photoelectron yield excited in the presence of resonance-enhanced X-ray propagation effect can provide depth dependent information about impurity distribution and processes in thin layers.
Źródło:
Acta Physica Polonica A; 1997, 91, 5; 851-857
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Transport and Magnetic Studies of New Mixed-Valence Compounds: K$\text{}_{3}$Cu$\text{}_{8}$Se$\text{}_{6}$, KCu$\text{}_{3}$Se$\text{}_{2}$, K$\text{}_{3}$Cu$\text{}_{8}$Te$\text{}_{6}$ and BaCuS$\text{}_{3-x}$
Autorzy:
Jacyna-Onyszkiewicz, I.
Sidowski, M.
Starodub, W.
Ratuszna, A.
Robaszkiewicz, S.
Powiązania:
https://bibliotekanauki.pl/articles/1955832.pdf
Data publikacji:
1997-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.20.-g
71.30.+h
Opis:
New mixed-valent copper chalcogenides BaCuS$\text{}_{3-x}$ and K$\text{}_{3}$Cu$\text{}_{8}$X$\text{}_{6}$ with X=Se or Te and KCu$\text{}_{3}$Se$\text{}_{2}$, with chemical patterns corresponding to the recently investigated K$\text{}_{3}$Cu$\text{}_{8}$S$\text{}_{6}$ and KCu$\text{}_{3}$S$\text{}_{2}$, were synthesized. For these new samples the results of resistivity and magnetic susceptibility measurements are presented. For BaCuS$\text{}_{3-x}$, K$\text{}_{3}$Cu$\text{}_{8}$Se$\text{}_{6}$ and KCu$\text{}_{3}$Se$\text{}_{2}$ the metal-insulator transition is observed with the low temperature phase being metallic, which is untypical, whereas K$\text{}_{3}$Cu$\text{}_{8}$Te$\text{}_{6}$ is a metal in the investigated temperature range. The temperature dependence of magnetic susceptibility of the studied samples testifies to their diamagnetic or weakly paramagnetic behaviour.
Źródło:
Acta Physica Polonica A; 1997, 91, 2; 405-408
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Low-Temperature Structural Phase Transition in Monoclinic RbDy(WO$\text{}_{4}$)$\text{}_{2}$ Crystal
Autorzy:
Borowiec, M. T.
Dyakonov, V.
Kamenev, V.
Nabiałek, A.
Prokhorov, A.
Szymczak, H.
Załęski, M.
Powiązania:
https://bibliotekanauki.pl/articles/1968975.pdf
Data publikacji:
1998-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
76.30.-v
75.20.-g
Opis:
The ESR spectrum of Dy$\text{}^{3+}$ ion in the low-symmetry RbDy(WO$\text{}_{4}$)$\text{}_{2}$ crystal has been studied in the temperature region of T=4.2 ÷ 30K. The ESR linewidth was found to increase from 130 mT up to the maximum value of 190 mT at T=9K and then to decrease down to 150 mT at 4.2K. The components of the g-tensor change considerably without change of their spatial orientation in the temperature range from 12K to 7 K: g$\text{}_{z}$=2.5, g$\text{}_{x}$≈0, g$\text{}_{y}$=1.41 at T>12 K; g$\text{}_{z}$=1.53, g$\text{}_{x}$≈0, g$\text{}_{y}$=1.2 at T<7K. The observed λ-shaped behaviour of absorption linewidth and the decrease in the g-factor are assumed to be due to the low-temperature structural phase transition (T$\text{}_{SPT}$≈9 K). The width of the transition area is of about 5K. It is suggested that the symmetry of high- and low-temperature phases is identical.
Źródło:
Acta Physica Polonica A; 1998, 94, 1; 71-77
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Optical Properties and Microstructure of InGaN Grown by Molecular Beam Epitaxy
Autorzy:
Böttcher, T.
Einfeldt, S.
Figge, S.
Kirchner, V.
Hommel, D.
Selke, H.
Ryder, P. L.
Bertram, F.
Riemann, T.
Christen, J.
Lunz, U.
Becker, C. R.
Powiązania:
https://bibliotekanauki.pl/articles/1969025.pdf
Data publikacji:
1998-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
68.35.Dv
68.65.+g
78.20.-e
78.55.-m
78.55.Cr
Opis:
The luminescence of In$\text{}_{x}$Ga$\text{}_{1-x}$N is studied for thick epitaxial layers and quantum wells. Using spatially resolved cathodoluminescence spectroscopy the commonly observed broad integral photoluminescence spectra were found to result from spectral and lateral inhomogeneous emission across the samples. Moreover, the integral photoluminescence and absorption spectra show different temperature dependences. The effects can be explained assuming fluctuations of the composition associated with a variation of the band gap.
Źródło:
Acta Physica Polonica A; 1998, 94, 2; 260-264
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 119

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