Dispersive Gap Mode of Phonons in Anisotropic Superconductors

TL;DR

This paper investigates how anisotropic superconducting gaps influence phonon dispersive modes in borocarbide superconductors, revealing that sign changes in pairing functions suppress certain phonon modes and that these observations can elucidate pairing mechanisms.

Contribution

It provides a numerical analysis of the impact of gap anisotropy and sign changes on phonon dispersive modes, offering insights into superconducting pairing functions.

Findings

Sign change in pairing function suppresses the dispersive gap mode.

Superconductivity reduces phonon softening at the Kohn anomaly.

Observation of the gap mode helps identify pairing symmetry.

Abstract

We estimate the effect of the superconducting gap anisotropy in the dispersive gap mode of phonons, which is observed by the neutron scattering on borocarbide superconductors. We numerically analyze the phonon spectrum considering the electron-phonon coupling, and examine contributions coming from the gap suppression and the sign change of the pairing function on the Fermi surface. When the sign of the pairing function is changed by the nesting translation, the gap mode does not appear. We also discuss the suppression of the phonon softening of the Kohn anomaly due to the onset of superconductivity. We demonstrate that observation of the gap dispersive mode is useful for sorting out the underlying superconducting pairing function.