Vortex Core Size in $^3$He-$^4$He films with Monolayer Superfluid $^4$He

TL;DR

This study investigates how the vortex core size in $^3$He-$^4$He films varies with $^3$He coverage, revealing a linear increase below one layer and emphasizing the importance of annealing for film homogeneity.

Contribution

It provides new insights into vortex core size behavior in superfluid helium films with varying $^3$He coverage, highlighting the effects of annealing on film uniformity.

Findings

Vortex core size increases linearly with $^3$He coverage below one layer.

Annealing at 4.2 K is crucial for film homogeneity.

Transition broadening correlates with $^3$He coverage.

Abstract

The superfluid transition of $^3$He-$^4$He mixture films adsorbed on alumina powder is studied, with a $^4$He superfluid coverage near one layer. With up to 1.3 layers of $^3$He added, the transition becomes strongly broadened, indicating a linear increase in the vortex core size for $^3$He coverages below one layer. Annealing of the sample mixture at 4.2 K is found to be critically important in ensuring a homogeneous film across the porous substrate.