Energy Gaps and Kohn Anomalies in Elemental Superconductors

TL;DR

This study investigates how acoustic phonon lifetimes in elemental superconductors Pb and Nb relate to superconducting energy gaps and Fermi-surface nesting anomalies, revealing electron correlations beyond standard theories.

Contribution

It provides experimental evidence linking superconducting gaps with Kohn anomalies and suggests a new mechanism involving density-wave fluctuations affecting superconductivity.

Findings

Superconducting energy gaps converge with Kohn anomalies at low temperatures.

Electron correlations beyond standard models are indicated.

Possible interplay between superconductivity and density-wave fluctuations.

Abstract

The momentum and temperature dependence of the lifetimes of acoustic phonons in the elemental superconductors Pb and Nb was 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.