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Originally published in Science Express on 21 February 2008
Science 14 March 2008:
Vol. 319. no. 5869, pp. 1509 - 1512
DOI: 10.1126/science.1154115
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Reports

Energy Gaps and Kohn Anomalies in Elemental Superconductors

P. Aynajian,1 T. Keller,1,2 L. Boeri,1 S. M. Shapiro,3 K. Habicht,4 B. Keimer1*

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.

1 Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
2 ZWE FRM-II, Technical University of Munich, Lichtenbergstrasse 1, D-85748 Garching, Germany.
3 Brookhaven National Laboratory, Upton, NY 11973–5000, USA.
4 Hahn Meitner Institute, Glienicker Strasse 100, D-14109 Berlin, Germany.

* To whom correspondence should be addressed. E-mail: b.keimer{at}fkf.mpg.de

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Science. ISSN 0036-8075 (print), 1095-9203 (online)