Effect of 3He impurities on the mass decoupling of 4He films

TL;DR

This study investigates how small amounts of 3He impurities affect the mass decoupling behavior of superfluid 4He films on Grafoil, revealing sensitive impurity effects on superfluid properties and dislocation dynamics.

Contribution

It demonstrates the impact of 3He impurities on mass decoupling and superfluid counterflow suppression in 4He films, highlighting impurity-induced changes in superfluid behavior.

Findings

Mass decoupling is highly sensitive to 3He doping.

3He atoms cause a drop in resonance frequency at T3 ~0.4 K.

Reentrant mass decoupling occurs at TR near T3 with larger amplitudes.

Abstract

We carried out quartz crystal microbalance experiments of a 5 MHz AT-cut crystal for superfluid 4He films on Grafoil (exfoliated graphite) with a small amount of 3He up to 0.40 atoms/nm2. We found that the mass decoupling from oscillating substrate is considerable sensitive even in a small amount of 3He doping. In a 4He film of 29.3 atoms/nm2, we observed a small drop in resonance frequency at T3 of ~0.4 K for a small amplitude, which is attributed to sticking of 3He atoms on the 4He solid atomic layer. For a large amplitude, the 4He solid layer shows a reentrant mass decoupling at TR close to T3. This decoupling can be explained by the suppression of the superfluid counterflow due to the adsorption of 3He atoms on edge dislocations. As the 4He areal density increases, TR shifts to the lower temperature, and vanishes around a 4He film of 39.0 atoms/nm2.