Temat: 20-27 - Katalog OPAC zbiorów

Tytuł:: Valence Band of $Ce_2Co_{0.8}Si_{3.2}$ and $Ce_2RhSi_3$ Studied by Resonant Photoemission Spectroscopy and FPLO Calculations
Autorzy:: Starowicz, P.
Kurleto, R.
Goraus, J.
Walczak, Ł.
Penc, B.
Adell, J.
Szlawska, M.
Kaczorowski, D.
Szytuła, A.
Powiązania:: https://bibliotekanauki.pl/articles/1374249.pdf
Data publikacji:: 2014-10
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.27.+a
75.30.Mb
71.20.Eh
74.25.Jb
Opis:: This work presents studies of the valence band of two Kondo lattice systems: $Ce_2Co_{0.8}Si_{3.2}$, which is paramagnetic with the Kondo temperature $T_{K}$ ≈50 K and $Ce_2RhSi_3$, which is antiferromagnetic below $T_{N}$=4.5 K and exhibits $T_{K}$ ≈9 K. The photoemission spectra, which are obtained with photon energy tuned to Ce 4d-4f resonance, reveal a Kondo peak at the Fermi energy $(E_{F})$, its spin-orbit splitting partner at 0.24 eV and a broad maximum related to Ce $f^0$ final state. The spectra indicate that Kondo peak has a higher intensity for $Ce_2Co_{0.8}Si_{3.2}$. The off-resonance photoemission data reveal that a maximum in the 3d electron density of states is shifted towards $E_{F}$ for $Ce_2Co_{0.8}Si_{3.2}$ as compared to $Ce_2RhSi_3$. Full-potential local-orbital calculations were realized with local spin density approach +U approach for 213 stoichiometry. They show that a higher density of states near $E_{F}$ is observed for $Ce_2CoSi_3$. The calculations also reveal the existing tendencies for antiferromagnetic and ferromagnetic ground states in a case of $Ce_2RhSi_3$ and $Ce_2CoSi_3$, respectively.
Źródło:: Acta Physica Polonica A; 2014, 126, 4a; A-144-A-147
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 12.

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

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Skocz do pozycji: 13.

Tytuł:: Unconventional Superconducting States of an Almost Localized Fermionic Liquid with Nonstandard Quasiparticles: Generalized Gutzwiller Approach
Autorzy:: Kaczmarczyk, J.
Jędrak, J.
Spałek, J.
Powiązania:: https://bibliotekanauki.pl/articles/1536614.pdf
Data publikacji:: 2010-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
71.27.+a
71.10.Ca
Opis:: We apply the concept of generalized (almost localized) Fermi liquid and associated with it unconventional superconductivity with Cooper pairs composed of quasiparticles with the spin dependent masses (in an applied field) and with the effective field, both induced by electron correlations. The pairing among quasiparticles takes place either in reciprocal space (Sect. 2) or in real space (Sect. 3) and is induced by the kinetic exchange of either superexchange (in the generic narrow-band situation) or Kondo-type interaction (in the Kondo-lattice limit of the periodic Anderson model). While the main features of this type of Fermi liquid have been introduced earlier, we present here a picture which is applicable to both heavy-fermion and high-$T_{c}$ superconductivity within a single narrow-band representation of correlated states. Our approach introduces a set of additional concepts (spin-dependent masses, effective fields induced by electron correlations), for which the Landau concept of the Fermi liquid represents still a workable scheme. In the limit of the Kondo lattice, we present the phase diagram incorporating the Fulde-Ferrell-Larkin-Ovchinnikov phase within the BCS-type of pairing, whereas in that of the t-J model we show that the proper choice of renormalization factors and constraints is crucial for the mean-field description of the superconducting state.
Źródło:: Acta Physica Polonica A; 2010, 118, 2; 261-266
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 14.

Tytuł:: Theory of Unconventional Superconductivity in Strongly Correlated Systems: Real Space Pairing and Statistically Consistent Mean-Field Theory - in Perspective
Autorzy:: Spałek, J.
Powiązania:: https://bibliotekanauki.pl/articles/1431227.pdf
Data publikacji:: 2012-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.27.+a
74.70.Tx
74.20.-z
Opis:: In this brief overview we discuss the principal features of real space pairing as expressed via corresponding low-energy (t-J or periodic Anderson-Kondo) effective Hamiltonian, as well as consider concrete properties of those unconventional superconductors. We also rise the basic question of statistical consistency within the so-called renormalized mean-field theory. In particular, we provide the phase diagrams encompassing the stable magnetic and superconducting states. We interpret real space pairing as correlated motion of fermion pair coupled by short-range exchange interaction of magnitude J comparable to the particle renormalized band energy ≈ tx, where x is the carrier number per site. We also discuss briefly the difference between the real-space and the paramagnon-mediated sources of superconductivity. The paper concentrates both on recent novel results obtained in our research group, as well as puts the theoretical concepts in a conceptual as well as historical perspective. No slave-bosons are required to formulate the present approach.
Źródło:: Acta Physica Polonica A; 2012, 121, 4; 764-784
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 15.

Tytuł:: The Effects of Relativistic Warm Plasma Waveguide and High Frequency Electrical Field on Beam-Plasma Interaction
Autorzy:: El-Shorbagy, Kh. H.
Powiązania:: https://bibliotekanauki.pl/articles/2047358.pdf
Data publikacji:: 2007-07
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 52.27.Ny
52.35.-g
94.20.wf
Opis:: The paper is concerned with investigation of the influence of an intense high frequency electric field and relativistic warm plasma waveguide on electrostatic oscillations of nonuniform bounded plasma. The stabilizing effect of a strong high frequency (pump) electrical field on beam-plasma interaction in a cylindrical relativistic warm plasma waveguide is discussed. A new mathematical technique "separation method" was applied to the two-fluid plasma model to separate the equations, which describe the system, into two parts, time and space parts. Plasma electrons are considered to have a relativistic, thermal velocity. It is shown that a high frequency electric field has no essential influence on dispersion characteristics of unstable surface waves excited in a relativistic warm plasma waveguide by a low-density electron beam. The region of instability is only slightly narrowing and the growth rate decreases by a small parameter and this result was reduced comparing to cold, nonrelativistic plasma. Also, it is found that the plasma electrons did not affect the solution of the space part of the problem.
Źródło:: Acta Physica Polonica A; 2007, 112, 1; 41-48
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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