Energy Gaps and Kohn Anomalies in Elemental Superconductors

Science  14 Mar 2008:
Vol. 319, Issue 5869, pp. 1509-1512
DOI: 10.1126/science.1154115

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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.

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