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    Wyświetlanie 1-7 z 7
    Tytuł:
    Resonance Raman Investigations of Low Energetic Modes in the Organic Superconductors α$\text{}_{t}$-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$ and β-(BEDT-TTF)$\text{}_{2}$IAuI
    Autorzy:
    Ludwig, T.
    Schweitzer, D.
    Keller, H. J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933367.pdf
    Data publikacji:
    1995-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.30.-j
    74.70.Kn
    Opis:
    A study of low energetic modes in the resonance Raman spectra of the organic superconductors α$\text{}_{t}$-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$ (T$\text{}_{c}$ = 8 K) and β-(BEDT-TTF)$\text{}_{2}$IAuI (T$\text{}_{c}$ = 4 K) in the temperature range of 1.5-100 K was performed. In both materials, a strong vanishing of low energetic phonon bands (at 30 cm$\text{}^{-1}$ and 40 cm$\text{}^{-1}$ for α$\text{}_{t}$-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$ and at 27 cm$\text{}^{-1}$ and 33 cm$\text{}^{-1}$ for β-(BEDT-TTF)$\text{}_{2}$IAuI) below 71 was observed. For the symmetric stretching mode of the I¯$\text{}_{3}$ and the IAuI¯ anion at 120 cm$\text{}^{-1}$ no change below T, was found. In addition, wavelength dependent measurements on α-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$ were performed, indicating that the modes around 30 cm$\text{}^{-1}$ are probably librational modes of the BEDT-TTF molecules.
    Źródło:
    Acta Physica Polonica A; 1995, 87, 4-5; 801-806
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Investigations of Fermi Surfaces and Effective Masses of the Organic Superconductors (BEDO-TTF)$\text{}_{2}$ReO$\text{}_{4}$(H$\text{}_{2}$O) and κ-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$ by Shubnikov-de Haas and de Haas-van Alphen Measurements
    Autorzy:
    Schweitzer, D.
    Balthes, E.
    Karlich, S.
    Heinen, I.
    Keller, H.
    Strunz, W.
    Biberacher, W.
    Jansen, A.G.M.
    Steep, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933332.pdf
    Data publikacji:
    1995-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.25.Jd
    71.25.Hc
    74.70.Kn
    Opis:
    The Fermi surfaces and effective masses of (BEDO-TTF)$\text{}_{2}$ReO$\text{}_{4}$(H$\text{}_{2}$0) and κ-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$ were investigated by Shubnikov–de Haas (SdH) and de Haas–van Alphen (dHvA) measurements in magnetic fields up to 27 T in the temperature range from 0.5 K to 4.2 K. Two small closed pockets (0.7% and 1.5% of the first Brillouin zone) are observed in (BEDO-TTF)$\text{}_{2}$ReO$\text{}_{4}$(H$\text{}_{2}$0) corresponding very well with two cross-sectional areas of the Fermi surfaces obtained for a hole and an electron pocket from tight binding calculations. In contrast, in κ-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$ two relatively large closed sections (13% and 85% of the first Brillouin zone) of the Fermi surfaces are observed, again confirming the tight binding calculations. For κ-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$ in magnetic fields above 12 T the effective mass for the larger orbit, as obtained from the temperature dependence of the SdH-oscillation amplitudes, is magnetic field dependent as long as the field is arranged perpendicular to the conducting planes (Θ = 0°). In contrast, from dHvA measurements - which were performed by turning the magnetic field by 27° with respect to the SdH experiments - the observed effective mass is field independent. We suppose that the occurrence of anyons at temperatures below 1 K and in fields above 12 T might be the reason for the observed field dependence of the effective mass in the SdH investigations under the special angle 0°.
    Źródło:
    Acta Physica Polonica A; 1995, 87, 4-5; 749-759
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Fabrication and Characterization of Thin Films of the Organic Superconductor α$\text{}_{t}$-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$
    Autorzy:
    Moldenhauer, J.
    Wachtel, H.
    Schweitzer, D.
    Gompf, B.
    Eisenmenger, W.
    Bele, P.
    Brunner, H.
    Keller, H. J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933377.pdf
    Data publikacji:
    1995-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.Kn
    73.50.-h
    81.15.Gh
    Opis:
    α-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$ is a quasi-two-dimensional organic metal with a metal-insulator phase transition at 135 K. Thermal treatment at about 80°C leads to the metallic system α$\text{}_{t}$-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$, which becomes superconducting below 8 K. Thin films of the α-phase (thickness between 500 and 3000 Å) have been evaporated in high vacuum onto several substrates and characterized by means of X-ray diffraction, scanning electron microscopy, atomic force microscopy and low field microwave absorption. Depending on the temperature of the substrate and the evaporation rate, the films exhibit different degrees of microcrystallinity, which under certain conditions can be strongly reduced and a completely covering film can be obtained. X-ray diffraction spectra reveal a high orientation with the c-axis perpendicular to the substrate and as well the successful conversion into the α$\text{}_{t}$-phase by tempering. Scanning electron microscopy and atomic force microscopy investigations prove that the conversion takes place without reducing the mechanical quality of the films. Low-field microwave-absorption experiments show that the α$\text{}_{t}$-films become superconducting with an onset at 9 K.
    Źródło:
    Acta Physica Polonica A; 1995, 87, 4-5; 823-827
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Optical Absorption of Polymer Films Doped with BEDT-TTF Polyiodides
    Autorzy:
    Helberg, H. W.
    Staerk, D.
    Ulański, J.
    Jeszka, J. K.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933405.pdf
    Data publikacji:
    1995-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.40.Ha
    78.30.Jw
    74.70.Kn
    Opis:
    Conducting reticulate doped polymeric films containing BEDT-TTF iodide crystalline network were annealed in order to transform the crystallites into crystal phases with metallic conductivity. Measured optical absorption spectra show that annealing shifts the absorption band to higher frequencies and increases the transparency of the films. This behavior corresponds to the transformation of the α-phase into the superconducting α$\text{}_{t}$-phase observed in (BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$ single crystals.
    Źródło:
    Acta Physica Polonica A; 1995, 87, 4-5; 893-897
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Magnetic Field Dependent Effective Mass in the Organic Superconductor κ-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$
    Autorzy:
    Balthes, E.
    Schweitzer, D.
    Heinen, I.
    Keller, H. J.
    Biberacher, W.
    Jansen, A. G. M.
    Steep, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933336.pdf
    Data publikacji:
    1995-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.Kn
    71.25.Hc
    71.25.Jd
    Opis:
    κ-(BEDT-TTF)$\text{}_{2}$I$\text{}_{3}$ is an electronically extreme two-dimensional organic metal with a superconducting transition at around 4 K. In magnetic fields above 12 T the effective mass, as obtained from the temperature dependence of the amplitudes of Shubnikov-de Haas oscillations, is magnetic field dependent as long as the magnetic field is arranged perpendicular to the conducting planes. In contrast to this, by turning the magnetic field by 27° or even only 9° the observed effective mass (as obtained from Shubnikov-de Haas and de Haas-van Alphen measurements) is field independent. We suppose that the occurrence of anyons at temperatures below 1 K in fields above 12 T is the reason for the observed field dependence of the effective mass.
    Źródło:
    Acta Physica Polonica A; 1995, 87, 4-5; 767-772
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Primary Role of Ionic Polarizability in Exotic Superconductivity
    Autorzy:
    Weger, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933315.pdf
    Data publikacji:
    1995-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.Kn
    74.72.-v
    72.15.-h
    71.45.Gm
    Opis:
    The ionic polarizability of organic metals and of high-T$\text{}_{c}$ cuprates is very high while the density of conduction electrons is low. As a result, the ionic polarizability screens out the electronic polarizability for states very close to the Fermi surface. The cut-off is determined by the dispersion of the ionic polarizability. The electron-phonon matrix element is very large for the ionically screened states, and is the cut-off for the electronically screened states. Therefore, the McMillan coupling constant λ$\text{}_{ph}$ is very large at very low energies, and has a low energy cut-off. This model accounts for both normal and superconducting state anomalies in organic metals, as well as cuprates.
    Źródło:
    Acta Physica Polonica A; 1995, 87, 4-5; 723-733
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Peculiarities of the Electronic Properties of the κ-Phase Structures (BEDT-TTF)$\text{}_{2}$Cu(N(CN)$\text{}_{2}$)X with X=Cl, Br, I
    Autorzy:
    Andres, K.
    Posselt, H.
    Kushch, N.
    Kund, M.
    Biberacher, W.
    Saito, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933335.pdf
    Data publikacji:
    1995-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    72.80.Le
    75.50.Gg
    75.50.Ee
    74.70.Kn
    Opis:
    The structure of the title compounds is similar to other κ-phase structures with respect to the checkerboard-like arrangement of the ET dimers (ET = BEDT-TTF) in the conducting planes, but different by the tilt alternation of these dimers in successive planes. The resulting inequivalence of these planes tends to destabilize the metallic state which becomes extremely sensitive to changes in the S-S overlaps of neighbouring ET molecules. Such changes may result from anion substitution, lattice expansion, or also from ordering effects of the ethylene end groups of the ET molecules. They lead to quite different electronic properties of the three isostructural compounds. We focus especially on the strongly pressure-dependent properties of the Cl-compound, where a coexistence of magnetically ordered and superconducting states with rather spectacular superconducting reentrance effects is observed.
    Źródło:
    Acta Physica Polonica A; 1995, 87, 4-5; 761-766
    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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