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 Experimental results on absolute phonon detection sensitivity of superconducting tunneling junctions(1972) Trumpp, Hans-Joachim; Epperlein, Peter W.; Lassmann, KurtSuperconducting tin tunnelling junctions are used for generating and detecting 300 GHz phonons. The absolute phonon detection sensitivity can be obtained, making possible a comparison of the number of phonons detected to the number of phonons generated. This, together with measurements of the dependence of junction time constant on its thickness, gives an indication that far more phonons are radiated into liquid He than is expected from a simple acoustic model.Item Open Access Reflection of high frequency phonons at free silicon surfaces(1978) Marx, Dieter; Buck, Jochen; Lassmann, Kurt; Eisenmenger, WolfgangIn reflection experiments at free silicon [100]-surfaces we could distinguish between specularly and diffusely reflected transverse phonons propagated along <100>-directions. With increasing phonon frequency the number of diffusely scattered phonons increase relative to that of specularly reflected phonons.Item Open Access Effective quasiparticle recombination times and electronic density of states at the Fermi level in superconducting films(1978) Epperlein, Peter W.; Lassmann, Kurt; Eisenmenger, Wolfgang-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 Resonance and relaxation attenuation by neutral acceptors in a magnetic field(1977) Schad, Hanspeter; Lassmann, Kurt; Zeile, HeinrichFine 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.Item Open Access Ultrasonic attenuation due to the neutral acceptor Mn in GaAs(1976) Lassmann, Kurt; Schad, HanspeterWe report on measurements of the ultrasonic attenuation in GaAs: Mn at frequencies between 400 and 2000 MHz and at temperatures between 1 and 35 K. The results indicate that there is a level 3 meV above the acceptor round state.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 Anisotropy of phonon emission from hot electrons in germanium(1976) Reupert, Wolfram; Lassmann, Kurt; Groot, Peter deWe have measured quantitatively the anisotropy of the electron-acoustical phonon scattering in n-germanium in five directions of the (lTO) plane utilizing tunneling junctions for calibrated detection of the phonon radiation emitted from a small avalanche breakdown region in the germanium surface. For comparison and evaluation of phonon focusing a constantan heater and a tunneling junction were also used as phonon sources. A similar experiment has been reported by A. Zylbersztejn, but he could only compare the ratio of the amplitudes of longitudinal and transverse phonon pulses in a given crystal direction to the calculation.