Second sound spectroscopy of a nonequilibrium superfluid-normal interface

TL;DR

This paper proposes an experiment to test a theory predicting a resonant second sound mode at a superfluid-normal interface, revealing new interfacial dynamics and fluctuation effects in nonequilibrium superfluid systems.

Contribution

It introduces an experimental approach to verify a hydrodynamic theory of nonequilibrium superfluid-normal interfaces, focusing on the detection of a predicted second sound resonance mode.

Findings

Resonant dip in reflected second sound signal at interface

Slow power-law dependence of order parameter on distance from interface

Prediction of a trapped second sound mode at the interface

Abstract

An experiment is proposed to test a previously developed theory of the hydrodynamics of a nonequilibrium heat current-induced superfluid-normal interface. It is shown that the interfacial ``trapped'' second sound mode predicted by the theory leads to a sharp resonant dip in the reflected signal from an external second sound pulse propagated towards the interface when its horizontal phase speed matches that of the interface mode. The influence of the interface on thermal fluctuations in the bulk superfluid is shown to lead to slow power dependence of the order parameter, and other quantities, on distance from it.