Electric potential of the electron sound wave: Sharp disappearance in the superconducting state

TL;DR

This study investigates the ac electric potential generated by electron sound waves in high-purity gallium, revealing a sharp disappearance of this potential in the superconducting state, linked to different behaviors of potential and elastic components.

Contribution

It provides a multiband model explanation for the distinct temperature dependencies of potential and elastic displacement in electron sound waves.

Findings

Potential phase increases with temperature.

Elastic displacement phase decreases with temperature.

Potential disappears abruptly below T_c in the superconducting state.

Abstract

We study the ac electric potential induced by the electron sound wave (a perturbation of the electron distribution function propagating with the Fermi velocity) in single crystals of high purity gallium. The potential and the elastic components of the electron sound demonstrate qualitatively different dependencies on the electron relaxation rate: while the phase of the potential increases with temperature, the phase of elastic displacement decreases. This effect is explained within the multiband model, in which the potential is attributed to the ballistic quasiwave, while the elastic component is associated with the zero-sound wave. We observed a mysterious property of the superconducting state: all manifestations of the potential accompanying the lattice deformations, including usual sound wave, disappear below T_c in almost jumplike manner.