Browsing by Author "Heim, Ulrich"

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    Enhancement of the Kapitza conductance at 0.32 meV phonon energy
    (1983) Heim, Ulrich; Schweizer, Rainer J.; Koblinger, Otto; Welte, Michael; Eisenmenger, Wolfgang
    Using quasimonochromatic relaxation phonons emitted by superconducting tunneling functions, the phonon transfer through real solid-liquid helium interfaces was tested. We found an enhancement of the energy transmission if the incident phonons exceed the threshold energy Eo = 0.32 meV. This sharp threshold energy shifts to 0.42 meV if the lighter isotope 3 He is used.
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    Observation of phonon frequency thresholds in the anomalous Kapitza resistance
    (1983) Koblinger, Otto; Heim, Ulrich; Welte, Michael; Eisenmenger, Wolfgang
    Phonons emitted by superconducting tunneling junctions into insulator crystal substrates exhibit a sharp amplitude reduction above 85 GHz if the tunneling diodes are covered by 4He. This is attributed to the onset of an enhanced phonon transport into helium.
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    Spectral dependence of the Kapitza resistance between O,5 K and 2,3 K
    (1984) Koblinger, Otto; Dittrich, Ehrenfried; Heim, Ulrich; Welte, Michael; Eisenmenger, Wolfgang
    Summarizing, we observed strongly enhanced phonon transport from a real solid into 4 He starting at about 85 GHz which is independent of the He gas pressure up to liquid helium. With the isotope 3 He the onset frequency for enhanced phonon transport shifts to 100 GHz. The threshold frequencies are almost independent of the He temperature in the range between 0.5 K and 2.3 K. Only slight shifts to lower frequencies with decreasing He temperature have been observed. No significant influence of the generator material (Sn, Al, SiO) or the generator preparation on the onset frequency has been observed. Moreover at low temperatures and thin He films we observed an additional structure which might be interpreted as film thickness resonances in the He film layer on the generator.