The Plastic Flow of Solid 4He through a Porous Membrane

TL;DR

This study measures the flow of solid helium-4 through a porous membrane across a range of temperatures, revealing a transition from classical vacancy-driven flow to quantum plastic flow at low temperatures.

Contribution

It provides the first experimental evidence of a transition from classical to quantum plastic flow in solid helium-4.

Findings

Flow velocity decreases with temperature above 1K following Arrhenius law.

Below 1K, flow velocity becomes temperature-independent.

Transition indicates a shift from vacancy-mediated to quantum plastic flow.

Abstract

The flow velocity of solid 4He through a porous membrane frozen into a crystal has been measured in the temperature interval 0.1 - 1.8 K. A flat capacitor consisting of a metalized plastic porous membrane and a bulk electrode is applied and the gap in the capacitor was filled with examined helium. The flow of helium through the membrane pores is caused by a d.c. voltage applied to the capacitor plates. Above T~1K the velocity of solid 4He flow decreases with lowering temperature following the Arrhenius law with the activation energy of the process closed to that of vacancies. At low temperatures the velocity is practically independent of temperature, which suggests a transition in 4He from the classical thermally activated vacancy-related flow to the quantum plastic flow.