Universität Stuttgart
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Item Open Access Quasiparticle recombination and 2Δ-phonon-trapping in superconducting tunnelling junctions(1976) Eisenmenger, Wolfgang; Lassmann, Kurt; Trumpp, Hans-Joachim; Krauß, RichardThe experimental recombination lifetime τeff of quasiparticles in superconducting films in general exceeds the intrinsic recombination lifetime τR by phonon trapping. On the basis of geometric acoustic propagation and reabsorption of phonons emitted in quasiparticle recombination, τeff is calculated as a function of film thickness d taking into account longitudinal and transverse phonon reabsorption, bulk loss processes and acoustical phonon transmission into the substrate. With increasing thickness d three characteristic ranges are found: range 1 with film thickness d small compared to the phonon reabsorption mean free path Λw, range 2 with d larger than Λw and dominating boundary losses, and range 3, also with d larger than Λw but with dominating bulk losses. For very small d the relation between τeff and τR, the intrinsic recombination lifetime, contains only the limiting angle of total reflection of phonons within the superconducting film. Therefore, τR can be directly obtained by τeff measurements and from the sound velocities of the film-substrate system. Range 2 is characterized by a linear dependence of τeff on d. In this range it is not possible to obtain τR from τeff measurements, however, τeff allows a determination of the phonon boundary transmission. Range 3 shows no thickness dependence of τeff on d in the limit of large d values. In this range a further method for obtaining τR from τeff values is suggested.Item Open Access Intrinsic and experimental quasiparticle recombination times in superconducting films(1977) Eisenmenger, Wolfgang; Lassmann, Kurt; Trumpp, Hans-Joachim; Krauß, RichardExperimental 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.Item Open Access Emission of high frequency relaxation phonons by superconducting aluminium tunneling junctions(1972) Welte, Michael; Lassmann, Kurt; Eisenmenger, WolfgangUp to now the emission of relaxation phonons of energy E > 2 Δ by tin tunnelling junctions could not be observed by reason of the strong reabsorption of such phonons in the generator junction. We now report experiments in which the emission of relaxation phonons of energy E > 2 Δ by aluminium tunnelling junctions is observed. The conditions necessary for the emission of high frequency relaxation phonons are discussed.Item Open Access Phonon emission by quasiparticle decay in superconducting tunnel junctions(1970) Kinder, Helmut; Lassmann, Kurt; Eisenmenger, WolfgangImproved measurements on phonon emission and detection by tunnel junctions show qualitative agreement with a numerical evaluation of Tewordt's theory on quasiparticle lifetime.Item Open Access Transmission of heater generated high frequency phonons through a sapphire-He II boundary(1974) Buck, Jochen; Lassmann, Kurt; Eisenmenger, WolfgangWe report on a new method to measure the absolute transmission coefficient through a solid-He II-boundary by determining absolutely the temperature amplitude of the second sound pulses in the liquid.Item Open Access Messung der Hyperschalldämpfung in Quarz(1965) Eisenmenger, Wolfgang; Kinder, Helmut; Lassmann, KurtZur Bestimmung der Hyperschalldämpfung in zylindrischen Quarzstäben für Longitudinalwellen in x-Richtung werden zwei Meßanordnungen für den Frequenzbereich 0,5 GHz bis 2.5GHz sowie für die Frequenz von 1O GHz bei Temperaturen von 4° K bis 273° K beschrieben. Im niedrigeren Frequenzbereich erfolgte eine Rauschbefreiung des Empfangssignals durch elektronische Abtastung und Summation. Neben der Temperatur- und Frequenzabhängigkeit der Dämpfung wurden Geometrieeinflüsse bei der Hyperschallanregung und Ausbreitung näher untersucht. Dabei traten Modeninterferenz und Keilwinkelfehler (Parallelitätsabweichungen der Stabendflächen) besonders deutlich in Erscheinung.Item Open Access Transition of 280 GHz phonons from superconducting tunneling junctions into liquid helium and silicon(1972) Trumpp, Hans-Joachim; Lassmann, Kurt; Eisenmenger, WolfgangComparative phonon emission experiments carries out in liquid helium and vacuum with superconducting tin-tin tunneling junctions evaporated on silicon crystals, show a transmission into helium about three times higher than the transmission into silicon.