Universität Stuttgart

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Start date: 1977End date: 1977Institute: search.filters.UBSInstitut.1. Physikalisches Institut

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    Energy gap reduction in superconducting tin films by quasiparticle injection
    (1977) Fuchs, Jürgen; Epperlein, Peter W.; Welte, Michael; Eisenmenger, Wolfgang
    In Sn-/-Sn-/-Pb tunneling structures the energy gap ΔSn of Sn is reduced by quasiparticle injection via single-particle tunneling between the Sn films. ΔSn as function of the quasiparticle density is probed by the Pb contact and found in agreement with the theory of Owen and Scalapino. An instability of the energy gap of Sn is observed at the critical gap reduction ratio predicted by this theory for a first-order phase transition.
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    Resonance and relaxation attenuation by neutral acceptors in a magnetic field
    (1977) Schad, Hanspeter; Lassmann, Kurt; Zeile, Heinrich
    Fine structure, level splitting, and relaxation times of the acceptor ground state in cubic semiconductors can be deduced from ultrasonic attenuation. By the application of a magnetic field it is possible to vary the coupling strength and the number of acceptors on speaking terms with the ultrasonic wave. Making use of this possibility, we have determined directly effective coupling constants for relaxation attenuation and the temperature dependence of the critical intensity for saturation of the resonant interaction. Results obtained for p-type GaAs and Si are discussed in comparison with analogous results for glasses.
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    Intrinsic and experimental quasiparticle recombination times in superconducting films
    (1977) Eisenmenger, Wolfgang; Lassmann, Kurt; Trumpp, Hans-Joachim; Krauß, Richard
    Experimental quasiparticle recombination lifetime data for superconducting Al, Sn, and Pb films are compared with calculations based on a ray acoustic model taking account of the film thickness dependence of the reabsorption of recombination phonons. Information on the true or intrinsic quasiparticle recombination lifetime obtained from these and other data is discussed.
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    Sources of loss processes in phonon generation and detection experiments with superconducting tunneling junctions
    (1977) Trumpp, Hans-Joachim; Eisenmenger, Wolfgang
    Observing the phonon yield, i.e. the ratio of the experimental phonon signal amplitude and the corresponding calculated value, phonon losses within the generation-detection system can be localized and determined quantitatively. With tin junctions on pure silicon substrates immersed in liquid helium the phonon yield is 3–5%. Under vacuum conditions the yield rises to 10–12% indicating strong phonon transmission to the helium bath. The experimental lifetime for 280 GHz phonons in the silicon substrate is longer than 65 µs indicating negligible volume losses and losses at the free substrate surface. It is further shown, that volume losses inside the phonon generator and detector are small compared to the total loss of about 90%. By phonon reverberation measurements we find evidence that the main sources for phonon losses are localized at the boundaries of the tunneling junctions to the substrate. This is supported by an increase of the phonon yield with improved polishing from about 9% (mechanical), 10% (chemical) to 12% (sputter etching). A SIMS analysis indicates the presence of carbonhydrates and probably of water in the boundaries. This layer of extraneous molecules together with the nonideal surface structure of the substrate and the evaporated films weakens the mechanical bonding between the tunnel junctions and the substrate and is possibly causing strong phonon splitting by anharmonic forces.