title: Energy gaps and Kohn anomalies in elemental superconductors.
abstract: The momentum and temperature dependence of the lifetimes of acoustic phonons in the elemental superconductors lead and niobium were determined by resonant spin-echo spectroscopy with neutrons. In both elements, the superconducting energy gap extracted from these measurements was found to converge with sharp anomalies originating from Fermi-surface nesting (Kohn anomalies) at low temperatures. The results indicate electron many-body correlations beyond the standard theoretical framework for conventional superconductivity. A possible mechanism is the interplay between superconductivity and spin- or charge-density-wave fluctuations, which may induce dynamical nesting of the Fermi surface.
authors.affiliation: Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Aynajian
authors.forename: T
authors.initials: T
authors.lastname: Keller
authors.forename: L
authors.initials: L
authors.lastname: Boeri
authors.forename: S M
authors.initials: SM
authors.lastname: Shapiro
authors.forename: K
authors.initials: K
authors.lastname: Habicht
authors.forename: B
authors.initials: B
authors.lastname: Keimer