Superconductivity-Induced Distortions of Phonon Lineshapes in Niobium

TL;DR

This study uses high-resolution neutron scattering to reveal that superconductivity causes complex changes in phonon lineshapes in niobium, supporting a theory that these effects are universal across different superconducting materials.

Contribution

It demonstrates that superconductivity-induced phonon lineshape distortions in niobium align with theoretical predictions and are not limited to specific compound classes.

Findings

Phonon lineshapes in niobium are affected by superconductivity beyond simple lifetime and frequency changes.

The observed lineshapes agree with the theory of Allen et al., indicating a universal phenomenon.

Superconductivity causes characteristic phonon lineshape distortions near the energy gap.

Abstract

Superconductivity-induced changes of phonon lineshapes in niobium have been re-investigated by high-resolution inelastic neutron scattering. We show that the changes go beyond a simple change in lifetime and frequency when the phonon frequency is close to the superconducting energy gap $2\Delta$. The observed lineshapes in elemental niobium are qualitatively similar to those found previously in borocarbide superconductors and agree very well with those predicted by the theory of Allen et al. [PRB 56, 5552 (1997)]. Our results indicate that the peculiar phonon lineshapes in the superconducting state predicted by the theory of Allen et al. are a general phenomenon and not restricted to a particular class of compounds.