Strong phonon softening without Fermi surface nesting

TL;DR

This paper reports the discovery of soft phonons in chromium away from nesting wavevectors, attributed to enhanced electron-phonon coupling, challenging the traditional view that phonon softening requires Fermi surface nesting.

Contribution

It demonstrates phonon softening without Fermi surface nesting, highlighting a new mechanism involving electron-phonon interactions in chromium and potentially other materials.

Findings

Uncovered soft phonons in chromium far from Q+-

LDA calculations show enhanced electron-phonon coupling causes anomalies

Suggests phonon anomalies can occur without Fermi surface nesting

Abstract

Interactions with electronic excitations can soften and/or broaden phonons. They are greatly amplified at wavevectors Q+- that connect parallel (nested) sheets of the Fermi surface. In such a case, called a Kohn anomaly, the phonon dispersion sharply dips and its linewidth has a maximum at Q+-. Here we present results of inelastic x-ray scattering measurements that uncovered soft phonons in chromium far from Q+-. They appear in addition to the previously reported soft phonons at Q+-. Calculations in the local density approximation (LDA) show that the new anomalies originate from enhanced electron-phonon coupling. A similar mechanism may explain phonon anomalies away from nesting wavevectors in copper oxide superconductors and other compounds.