Effect of superconducting fluctuations on ultrasound in unconventional superconductor

TL;DR

This paper investigates how superconducting fluctuations, influenced by order parameter symmetry and phonon polarization, affect ultrasound properties in layered unconventional superconductors, with implications for experimental measurements.

Contribution

It provides a comparative analysis of fluctuation effects on sound attenuation and velocity in s- and d-wave superconductors, incorporating both phenomenological and microscopic approaches.

Findings

Unconventional order parameter symmetry suppresses AL and MT fluctuation terms.

Transverse sound polarization reduces fluctuation corrections more than longitudinal.

Fluctuation effects can reverse the sign of sound velocity corrections above Tc.

Abstract

We study the renormalization of sound attenuation and sound velocity by fluctuation Cooper pairs in layered superconductors. We consider the influence of s- and d-wave symmetry of the fluctuating order parameter, on both longitudinal and transverse phonon modes. We show that both unconventional order parameter symmetry and transverse sound polarization suppress the AL and MT terms, while the DOS contribution is the least affected. The combination of these effects can change the sign of the overall fluctuation corrections above Tc. We also compare the results obtained using the Ginzburg-Landau formalism with a microscopic derivation of the fluctuation corrections to the sound velocity in both s- and d-wave superconductors. These calculations are motivated by ongoing ultrasound measurements in organic superconductors.