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    Wyświetlanie 1-8 z 8
    Tytuł:
    The van Hove Singularity and Two-Dimensional Superconductivity. Exact Analytical Results
    Autorzy:
    Szczęśniak, R.
    Grabiński, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2035542.pdf
    Data publikacji:
    2002-09
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.25.Kc
    Opis:
    We investigate a weak-coupling approach to superconductivity in the density of states that develops in the two-dimensional lattice with the van Hove singularity located at the Fermi level. Exact analytical expressions for the superconducting order parameter at zero temperature (Δ(0)) and for discontinuity in the specific heat at critical temperature (Δ C) were derived. We show that the presence of the logarithmic singularity hardly affects the ratio 2Δ(0)/kT$\text{}_{c}$, whereas the temperature dependence of Δ C can pronouncedly deviate from the standard BCS result.
    Źródło:
    Acta Physica Polonica A; 2002, 102, 3; 401-407
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electron Behaviour of $(Nd_{0.33}Eu_{0.2}Gd_{0.47})Ba_2Cu_3O_{y}$ Studied by Infrared Measurements
    Autorzy:
    Rameš, M.
    Železný, V.
    Phuoc, V.
    Gervais, F.
    Wolf, T.
    Jirsa, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1534787.pdf
    Data publikacji:
    2010-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.25.Gz
    74.20.Mn
    74.25.Kc
    Opis:
    Optical properties of a are $(Nd_{0.33}Eu_{0.2}Gd_{0.47})Ba_2$ $Cu_3O_y$ (NEG-123) single crystal interpreted in terms of the extended Drude model.
    Źródło:
    Acta Physica Polonica A; 2010, 118, 5; 938-939
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Phonon Drag and Carrier Diffusion Contributions in Thermoelectric Power of $M_3C_{60}$ (M = K, Rb) Fullerides
    Autorzy:
    Varshney, D.
    Singh, N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1400154.pdf
    Data publikacji:
    2013-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.Wz
    74.25.fg
    74.25.Kc
    Opis:
    The thermoelectric power (S) of $M_3C_{60}$ (M = K, Rb) alkali intercalated fullerides is theoretically investigated by considering the Mott expression within parabolic band approximation to reveal the electron diffusive thermoelectric power $(S_{c}^{diff})$. We follow the Fermi energy as electron parameter and $S_{c}^{diff}$ discerned linear temperature dependence. S infers a change in slope above transition temperature and becomes almost linear above 70 K for $M_3C_{60}$ alkali intercalated fullerides. As a next step, the phonon drag thermoelectric power $(S_{ph}^\text{drag})$ is computed within relaxation time approximation when thermoelectric power is limited by scattering of phonons from defects, grain boundaries, phonons and electrons as carriers. It is noticed that the $S_{ph}^\text{drag}$ of $K_3C_{60}$ is anomalous and it is an artifact of strong phonon-electron and -phonon scattering mechanism. The thermoelectric power within relaxation time approximation has been taken into account ignoring a possible energy dependence of the scattering rates. Behaviour of S(T) is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between carrier diffusion and phonon drag contributions in $M_3C_{60}$ (M = K, Rb) alkali intercalated fullerides.
    Źródło:
    Acta Physica Polonica A; 2013, 123, 4; 752-760
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Simple Band Model of Doped Fullerene Crystal
    Autorzy:
    Koper, A.
    Mucha, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2012907.pdf
    Data publikacji:
    2000-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.Mn
    74.25.Kc
    74.25.Jb
    Opis:
    We use quantum billiard with many scattering centers to describe conducting electrons properties in A$\text{}_{n}$C$\text{}_{60}$ crystals, where A denotes alkali metal. We focus our attention on the A$\text{}_{3}$C$\text{}_{60}$ crystal, for which we calculate the band structure, density of states, and conductivity for normal electrons. Conductivity shows linear dependence on temperature in this model, which agrees well with experimental data. We also discuss consequences of our results for superconductivity mechanism in A$\text{}_{3}$C$\text{}_{60}$ and possibilities of analogous approach to describe electron properties in fused fullerenes and multiply connected carbon clusters.
    Źródło:
    Acta Physica Polonica A; 2000, 97, 1; 233-236
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    On Strong Coupling Theory of Correlated Superconductors
    Autorzy:
    Wysokiński, K. I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1955487.pdf
    Data publikacji:
    1997-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    74.25.Kc
    74.20.Mn
    Opis:
    The strong coupling or Eliashberg equations of superconductivity have been generalised to describe strongly correlated systems. Calculations show that d-wave superconductivity is stable for small hole doping. It also follows that in correlated systems one should define three different Eliashberg functions and corresponding electron- phonon coupling constants λ$\text{}_{N}$, λ$\text{}_{S}$ and λ$\text{}_{tr}$ (to describe normal (N), superconducting (S) and transport (tr) properties) each of which is measured in different kind of experiment.
    Źródło:
    Acta Physica Polonica A; 1997, 91, 2; 329-332
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Pressure Effects on Electronic Structure of Iron Chalcogenide Superconductors $FeSe_{1-x}Te_x$
    Autorzy:
    Ciechan, A.
    Winiarski, M.
    Samsel-Czekała, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1431323.pdf
    Data publikacji:
    2012-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.Pq
    74.25.Kc
    74.62.F
    74.70.Xa
    Opis:
    We study the electronic structure of iron-based superconductors $FeSe_{1-x}Te_x$ within the density functional theory. We pay particular attention to the pressure effects on the Fermi surface (FS) topology, which seem to be correlated with a critical superconducting temperature $T_C$ of iron chalcogenides and pnictides. A reduction of the FS nesting between hole and electron cylinders with increasing pressure is observed, which can lead to higher values of $T_C$. The tellurium substitution into selenium sites yields FS changes similar to the pressure effect.
    Źródło:
    Acta Physica Polonica A; 2012, 121, 4; 820-823
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Anharmonicity and Weak Mode Assignment in La$\text{}_{2-x}$Sr$\text{}_{x}$CuO$\text{}_{4}$, with Oxygen Isotopic Substitution
    Autorzy:
    Siranidi, E.
    Lampakis, D.
    Palles, D.
    Liarokapis, E.
    Conder, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047249.pdf
    Data publikacji:
    2007-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.30.-j
    31.30.Gs
    74.25.Kc
    74.72.Dn
    Opis:
    The oxygen isotope effect on the first- and second-order Raman active modes of high-quality La$\text{}_{2-x}$Sr$\text{}_{x}$Cu$\text{}^{16,18}$O$\text{}_{4}$ (80% substitution $\text{}^{16}$O by $\text{}^{18}$O) polycrystalline compounds with x=0.00, 0.015 was investigated at low temperatures. In the second-order Raman scattering several weak and strong peaks were observed and assigned to oxygen atom vibrations. With the isotopic substitution the apex oxygen mode follows quite well the mass harmonic law at all temperatures studied, while the soft mode is anharmonic in the temperature range of 77-180 K and for higher temperatures its anharmonicity is strongly increased. The temperature dependence of the energy of the soft mode for x=0.0 shows also a modification at≈180 K and an abnormal behaviour at≈280 K, which may be related with the transition to the antiferromagnetic phase.
    Źródło:
    Acta Physica Polonica A; 2007, 111, 1; 173-177
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    $Ru_3Sn_7$: Phonon Reference for Superconducting $Mo_3Sb_7$
    Autorzy:
    Tran, V.
    Miiller, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/1810300.pdf
    Data publikacji:
    2009-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    65.40.-b
    72.15.Eb
    74.25.Kc
    74.25.Bt
    72.15.Qm
    Opis:
    In order to search for phonon reference for dimer-gapped superconducting $Mo_3Sb_7$, measurements of specific heat $(C_p(T))$ and electrical resistivity (ρ(T)) of $Ru_3Sn_7$ were performed in the temperature range 2-300 K. The phonon part of $C_p(T)$ and ρ(T) of $Ru_3Sn_7$ can satisfactorily be explained describing the spectrum with one Einstein and two Debye modes. We found $Θp_{E}$ ≈ 100 K, $Θp_{D1}$ ≈ 185 K and $Θp_{D2}$ ≈298 K. The magnetic specific heat of $Mo_3Sb_7$ exhibits a sharp maximum at T*= 50 K, below which follows a gap function. Magnetic resistivity increases as -lnT with decreasing temperature and shows maximum at T*.
    Źródło:
    Acta Physica Polonica A; 2009, 115, 1; 83-85
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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