Universität Stuttgart
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Item Open Access Spectral dependence of the Kapitza resistance between O,5 K and 2,3 K(1984) Koblinger, Otto; Dittrich, Ehrenfried; Heim, Ulrich; Welte, Michael; Eisenmenger, WolfgangSummarizing, 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.Item Open Access Down-conversion of high-frequency acoustic phonons(1987) Galkina, Tatjana I.; Blinov, A. Y.; Bonch-Osmolovskii, M. M.; Koblinger, Otto; Lassmann, Kurt; Eisenmenger, WolfgangMeasurements of phonon transport in amorphous media can give valuable information on the structural properties of these materials and may be of practical interest for its own concerning the question of thermalization in electronic devices. The existence of two-level systems in a-Si:H as one of these technically important materials has been concluded from measurements of dispersion and attenuation of acoustic surface waves.Item Open Access Enhancement of the Kapitza conductance at 0.32 meV phonon energy(1983) Heim, Ulrich; Schweizer, Rainer J.; Koblinger, Otto; Welte, Michael; Eisenmenger, WolfgangUsing 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.Item Open Access Phonon absorption-spectroscopy in the presence of strong elastic phonon scattering(1986) Mebert, Joachim; Koblinger, Otto; Döttinger, Siegfried; Eisenmenger, WolfgangIn this work we show that in the presence of a strong phonon scattering background absorption structures can only be well resolved by reducing sample thickness to the phonon mean free path. This mean free path can be determined by analyzing the pulse shape of 285 GHz phonons. By reducing sample thickness to the appropriate value of 0,3mm the 21,2 cm -1 crystalline field transition in CaF 2:Er 3+ could be evaluated with the very high resolution of 5 GHz. In experiments performed on a 1mm thick LaF 3 Er 3+ sample we observed an absoption line at 14,2 cm -1 not visible in FIR absorption measurements.Item Open Access Observation of phonon frequency thresholds in the anomalous Kapitza resistance(1983) Koblinger, Otto; Heim, Ulrich; Welte, Michael; Eisenmenger, WolfgangPhonons 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.