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    Wyświetlanie 1-7 z 7
    Tytuł:
    Studies on Isotope Shift Exponent and Pressure Coefficient for Extended Superconductors within BCS Formalism
    Autorzy:
    Banerjee, B.
    Roy, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1808029.pdf
    Data publikacji:
    2009-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.+f
    74.25.Bt
    74.25.Ha
    Opis:
    A tight-binding model comprising a hopping and an attractive interaction term was considered for high temperature superconductors. Explicit calculations on the effects of isotopic substitution of atoms and application of pressure on the transition temperatures were made in this work. Exact analytical expressions for the isotope-shift exponent (α) and pressure coefficient $(γ_P)$ of transition temperature $(T_C)$ considering the isotopic mass and pressure dependence of the hopping and attractive interaction strengths from a minimal model describing superconductivity were obtained. Theoretical predictions for α and $γ_P$ with proper choice of parameters are found to be qualitatively consistent with the results of the experiments of high $T_C$ oxides. The results depend on the band dispersion chosen.
    Źródło:
    Acta Physica Polonica A; 2009, 115, 5; 914-919
    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:
    Improved Transresistance Characteristics of Inductance-gate Type SFFT Using AFM Lithography
    Autorzy:
    Ko, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1400571.pdf
    Data publikacji:
    2015-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.Pq
    74.25.F-
    74.25.Jb
    74.55.+V
    Opis:
    An atomic force microscope (AFM) was used to locally anodize the serial channels of an inductance-gate type superconducting flux flow transistor (SFFT) as narrow slits with a width of 50 μm, a space of 25 μm, and 12 turns, to improve the transresistance value. Among the serial channels that were anodized with the scanning tip of the AFM in the drain current line, channels 1 and 2 were 7.3 and 7.9 μm wide, and 531 and 461 nm high, respectively. The critical current density in the serial channel of the fabricated SFFT, which was determined using an AFM modification method, was decreased by increasing the gate current. The measured current-voltage curves were compared with the simulated ones. The maximum transresistance value was 0.56 Ω at the drain current of 20 mA when the gate current was 6 mA. The transresistance characteristics of the inductance-gate type SFFT could be more improved than that of the single-channel type SFFT using an inductively coupled plasma lithography method
    Źródło:
    Acta Physica Polonica A; 2015, 127, 4; 928-930
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Remarks on the Hall Conductivity in Chiral Superconductors: Weak vs. Strong Coupling Approach
    Autorzy:
    Rogatko, M.
    Wysokiński, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/1374790.pdf
    Data publikacji:
    2014-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    74.25.F-
    74.70.Pq
    11.25.Tq
    Opis:
    We discuss the calculations of the ac Hall conductivity for superconductors with the time reversal symmetry breaking states. In the weak coupling theories these states show vanishing Hall response in one band models, even though one expects otherwise on symmetry grounds. On the other hand, the strong coupling approach based on the anti-de Sitter-conformal field theory correspondence leads to the non-vanishing Hall conductivity. We discuss the possible reasons of the discrepancy. The weak coupling many orbital theory leading to the Hall conductivity with correct temperature dependence is also briefly presented.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 4a; A-9-A-12
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Influence of Pressure on the Electron-Phonon Interaction in Superconductors
    Autorzy:
    Orendáč, Mat.
    Gabáni, S.
    Pristáš, G.
    Gažo, E.
    Shitsevalova, N.
    Flachbart, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/1030277.pdf
    Data publikacji:
    2017-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.Ad
    72.15.Eb
    74.62.Fj
    74.25.F-
    63.20.kd
    Opis:
    The electron-phonon interaction is a very important and ubiquitous process in solids, affecting almost all their physical properties. In metals, where the relaxation processes depend on both electrons and phonons, all thermodynamic and transport properties are dictated by the electron-phonon interaction. A very strong manifestation of the electron-phonon interaction is related with the superconducting state. Here we report the effect of high pressure on the transport electron-phonon interaction, λ_{tr}, in superconducting systems such as YB_6 (T_c ≈ 7.5 K), Pb (T_c ≈7.2 K), Nb bulk or thin film (T_c ≈9.2 K), and in LaB_6 in which superconductivity was not yet observed. The expected pressure effect should correspond to the theoretically predicted negative pressure effect on T_c (except for Nb thin film and LaB_6). To determine the influence of pressure on λ_{tr}, we utilized the Bloch-Grüneisen fit (denoted also as "thermal spectroscopy") of the precise temperature dependence of resistivity measurements in the normal state up to a pressure of 2.8 GPa. Based on this fit the observed negative pressure effect on λ_{tr} values, dλ_{tr}/dp, are as follows: dλ_{tr}/dp ≈-0.045 GPa^{-1} for YB_6, dλ_{tr}/dp ≈-0.13 GPa^{-1} for Pb, dλ_{tr}/dp ≈-0.019 GPa^{-1} or -0.028 GPa^{-1} for Nb bulk or thin film, respectively, and dλ_{tr}/dp ≈-0.003 GPa^{-1} for LaB_6.
    Źródło:
    Acta Physica Polonica A; 2017, 131, 4; 1039-1041
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Study of the Electronic Structure of CrPt$\text{}_{3}$ Alloy by the LMTO Method
    Autorzy:
    Szajek, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1924275.pdf
    Data publikacji:
    1992-12
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    65.40.-f
    71.10.+x
    74.20.Fg
    Opis:
    The ab initio self-consistent linear muffin-tin orbital calculations in the atomic sphere approximation have been performed for the ordered CrPt$\text{}_{3}$ (AuCu$\text{}_{3}$-type structure) alloy. The band structure and the densities of electronic states are presented. The para- and ferrimagnetic phases were considered. The spin-polarized calculations have confirmed the experimental observation of small antiparallel induced magnetic moment on a platinum atom.
    Źródło:
    Acta Physica Polonica A; 1992, 82, 6; 967-974
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Size Modification of Nanographite System of Activated Carbon Fibers Studied by EPR
    Autorzy:
    Kempiński, M.
    Kempiński, W.
    Śliwińska-Bartkowiak, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2043617.pdf
    Data publikacji:
    2005-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    42.81.Uv
    73.20.-r
    73.22.-f
    76.30.-v
    74.78.Na
    Opis:
    We report results of EPR measurements of activated carbon fibers. Experiments made for pristine activated carbon fibers and activated carbon fibers with adsorbed molecules (CCl$\text{}_{4}$, C$\text{}_{6}$H$\text{}_{5}$NO$\text{}_{2}$, and H$\text{}_{2}$O) confirmed the localized character of paramagnetic centers observed in the system. Pristine activated carbon fibers are characterized by single Lorentzian line. Broader component of EPR signal appears when guest molecules are adsorbed in nanopores. The strongest localization is observed for water-filled activated carbon fibers nanopores (with hydrophobic pore walls) where changes in distance between nanographite particles were monitored by the g-shift to higher values. This process is related to stronger spin-orbit interaction of electrons trapped at nanographite particles compressed by guest molecules.
    Źródło:
    Acta Physica Polonica A; 2005, 108, 2; 339-343
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-7 z 7

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