Hybrid sound modes in one-dimensional quantum liquids

TL;DR

This paper investigates the unique hybrid sound modes in one-dimensional quantum liquids, revealing two nearly identical sound modes that combine density and entropy oscillations, with their speed difference scaling linearly with temperature.

Contribution

It introduces the concept of hybrid first and second sound modes in 1D quantum liquids and characterizes their properties and temperature dependence.

Findings

Two hybrid sound modes exist in 1D quantum liquids.

The sound speeds are nearly equal, with a linear temperature difference.

The modes involve combined density and entropy oscillations.

Abstract

We study sound in a single-channel one-dimensional quantum liquid. In contrast to classical fluids, instead of a single sound mode we find two modes of density oscillations. The speeds at which these two sound modes propagate are nearly equal, with the difference that scales linearly with the small temperature of the system. The two sound modes emerge as hybrids of the first and second sounds, and combine oscillations of both density and entropy of the liquid.