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Subject: search.filters.subject.530Institute: search.filters.UBSInstitut.3. Physikalisches InstitutAuthor: search.filters.author.Schweitzer, DieterStart date: 1987End date: 1989

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Now showing 1 - 5 of 5
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    A stable superconducting state at 8K and ambient pressure in αt-(BEDT-TTF)2I3
    (1987) Schweitzer, Dieter; Bele, Petra; Brunner, Hermann; Gogu, Emil; Haeberlen, Ulrich; Hennig, Ingolf; Klutz, Thomas; Swietlik, Roman; Keller, Heimo J.
    We report bulk superconductivity at 8 K and ambient pressure in crystals of α t (BEDT-TTF)2I3. In contrast to the earlier observed metastable superconducting state at 8 K in crystals of β-(BEDT-TTF)2I3 here the superconducting state is stable and the crystals can be prepared by tempering α-(BEDT-TTF)2I3 above 70 °C for several days. ac-susceptibility measurements show that the observed superconducting state at 8 K is a bulk property of the crystals. Resistivity measurements indicate a sharp superconducting transition at 8 K with an onset temperature of about 9 K. The upper critical fields Hc2 at 1.3 K lie between 3 and 11 T depending on the direction of the magnetic field with respect to the crystal axes. ESR- as well as NMR-measurements indicate a total transformation of the α-phase crystals into the new superconducting α t -crystals after tempering.
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    Zero-field splittings of the two lowest excited electronic states in crystalline [Ru(bpy)3]X2 with X=PF6, ClO4
    (1989) Yersin, Hartmut; Gallhuber, Erich; Hensler, Gerold; Schweitzer, Dieter
    For the title compounds zero-magnetic field ODMR signals have been observed on the zero-phonon lines which correspond to the two lowest excited states and which result from Ru4d→bpyπ* charge-transfer transitions. The splitting into sublevels are of the order of 0.1 cm−1 and the corresponding electronic states may be classified as doubly degenerate on the basis of the usual resolution of the optical emission spectra. Several microwave resonances are detected and assigned to different sites of the [Ru(bpy)3]2+ chromophores. Small relaxation rates between the sublevels (compared to other excited-state deactivation rates) are found to be important for a description of the spectroscopic properties at low temperatures.
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    Some electronic properties of the organic superconductor β-(BEDT-TTF )2I3
    (1989) Cooper, John R.; Forró, Laszlo; Korin-Hamzic, Bojana; Miljak, Marko; Schweitzer, Dieter
    We report some results of magnetoresistance, magnetic susceptibility and magnetic anisotropy measurements on single crystals of the two dimensional organic superconductor βL-(BEDT-TTF)2I3 from 4.2 to 300 K. From the c* magnetoresistivity we deduce a value of 0.5 meV for the tight binding transfer integral tc, and show that there is significant conductivity anisotropy (a factor 5) in the a-b plane at low temperatures. A short value of the relaxation time, 0.5 ps at 9 K, indicates that electron transport between planes is becoming incoherent, which may affect the superconducting transition temperature. The static spin susceptibility shows little enhancement relative to the specific heat. The magnetic anisotropy data give evidence for a temperature dependent conduction electron diamagnetism when the magnetic field is perpendicular to the conducting planes.
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    Superconductivity at 7.5 K and ambient pressure in polycrystalline pressed samples of βp-(BEDT-TTF)2I3
    (1989) Schweitzer, Dieter; Gogu, Emil; Grimm, Hans; Kahlich, Siegfried; Keller, Heimo J.
    Recently, bulk superconductivity at ambient pressure in polycrystalline pressed samples of an organic metal - α-(BEDT-TTF)2I3 - was observed. This is a remarkable fact because this finding shows that organic superconductors can in principle be used for the production of electronic devices, such as squids, and might even be suitable for the preparation of superconducting cables similar to the high temperature superconductors of the copper oxides.
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    Zero-field splitting of the lowest excited state of [0s(bpy)3]2+ doped into [Ru(bpy)3](PF6)2
    (1989) Braun, Dieter; Schweitzer, Dieter; Yersin, Hartmut
    For the title compounds zero-magnetic field ODMR signals have been observed on the zero-phonon lines which correspond to the two lowest excited states and which result from Ru4d→bpyn* charge-transfer transitions. The splitting into sublevels are of the order of 0.1 cm-1 and the corresponding electronic states may be classified as doubly degenerate on the basis of the usual resolution of the optical emission spectra. Several microwave resonances are detected and assigned to different sites of the [Ru(bpy)3]2+ chromophores. Small relaxation rates between the sublevels (compared to other excited-state deactivation rates) are found to be important for a description of the spectroscopic properties at low temperatures.