Browsing by Author "Epperlein, Peter W."

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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
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Open Access
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.
Open Access
Experimental results on absolute phonon detection sensitivity of superconducting tunneling junctions
(1972) Trumpp, Hans-Joachim; Epperlein, Peter W.; Lassmann, Kurt
Superconducting 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.
Open Access
Measurements of effective quasiparticle recombination times and of densities of electronic states at the Fermi level in superconducting Al- and Pb-films
(1979) Epperlein, Peter W.; Eisenmenger, Wolfgang
Temperature-dependent quasiparticle recombination lifetimes tau exp (T) and densities N 0 of electronic states at the Fermi level have been measured from time decay experiments of excess quasiparticle concentrations in evaporated, superconducting Al- and Pb-tunnel junctions. Current pulses were used to inject excess, nonthermal quasiparticles in a single junction acting simultaneously as generator and detector. The experimental lifetimes in "unperturbed" Al show satisfactory agreement with calculations based on the 2Delta-phonon trapping lifetime model. Tau exp decreases with increasing perturbations of the Al film structure by oxygen background evaporation. In Pb the measured times indicate 2Delta-phonon volume losses. The densities N 0 in Pb-films and "unperturbed" as well as oxygen-perturbed Al-films differ by less than 5% from the corresponding bulk material data. Therefore, in trying to explain the enhancement of the transition temperature from 1.23 K to 1.85 K in perturbed, granular Al-films a change of N 0 can be ruled out.
Open Access
Quasiparticle recombination time in superconducting tin and normal electronic density of states at the Fermi surface from tunnel junction experiments
(1978) Epperlein, Peter W.; Lassmann, Kurt; Eisenmenger, Wolfgang
We have measured the temperature dependence of the effective quasiparticle recombination time in superconducting tin tunnel junctions by current and laser pulse excitation. The experimental times show satisfactory agreement with calculations based on the ray acoustic lifetime model of Eisenmenger et al. taking into account the film thickness dependence of the phonon reabsorption, 2Delta-phonon volume loss processes and phonon transmission from the junction into the substrate and liquid helium. On the basis of the BCS density of thermally excited quasiparticles and simplified rate equations for quasiparticle recombination, and from the analysis of measurements of decaying excess quasiparticle concentrations we obtain a mean valueN 0=(2.73±0.03) 1022 eV-1 cm-3 for the electronic density of states at the Fermi Surface in thin, evaporated tin films. This value differs less than 5% from that obtained from the experimental electronic heat-capacity coefficient of the bulk material.