Browsing by Author "Munnikes, Nathalie"

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    High resolution neutron spectroscopy of excitations in superconductors
    (2013) Munnikes, Nathalie; Keimer, Bernhard (Prof. Dr.)
    In this work, anomalies of acoustic phonons are studied in the elemental superconductors Nb and Pb and in lead-thallium and lead-bismuth. By using high-resolution spin-echo neutron spectroscopy, energy resolutions in the range of micro-eV were reached, which corresponds to an improvement of several orders of magnitude compared to conventional neutron spectroscopy. Several renormalization effects and anomalies appear at phonon energies near the energy gap and at temperatures above and below the superconducting transition temperature. Whereas the relative changes of the linewidths and energies agree well with predictions based on BCS theory, the absolute values differ significantly. Surprisingly, Kohn anomalies coincide with the saturated energy gap magnitude both in Nb and Pb. By means of neutron spectroscopy on several Pb1-xBix and Pb1-xTlx alloys, it could be demonstrated that the saturated energy gap follows the energy of the Kohn anomaly as it changes in the alloys.