Mass flow through solid 4He induced by the fountain effect

TL;DR

This study demonstrates mass flow through solid helium-4 induced by the fountain effect, indicating the presence of superfluidity within the solid and providing quantitative agreement with thermomechanical equilibrium predictions.

Contribution

The paper provides experimental evidence of superfluid-like mass flux through solid helium-4 and confirms the fountain effect's role in this phenomenon.

Findings

Mass flux appears near 600 mK and increases with decreasing temperature.

A sharp flux drop occurs near 75 mK, followed by an increase below this temperature.

Thermomechanical equilibrium consistent with the fountain effect is observed.

Abstract

Using an apparatus that allows superfluid liquid 4He to be in contact with hcp solid \4he at pressures greater than the bulk melting pressure of the solid, we have performed experiments that show evidence for 4He mass flux through the solid and the likely presence of superfluid inside the solid. We present results that show that a thermomechanical equilibrium in quantitative agreement with the fountain effect exists between two liquid reservoirs connected to each other through two superfluid-filled Vycor rods in series with a chamber filled with solid 4He. We use the thermomechanical effect to induce flow through the solid and measure the flow rate. On cooling, mass flux appears near T = 600 mK and rises smoothly as the temperature is lowered. Near T = 75 mK a sharp drop in the flux is present. The flux increases as the temperature is reduced below 75 mK. We comment on possible causes of this flux minimum.