Characterisation of superfluid vortices in helium II

TL;DR

This paper visualizes and characterizes superfluid vortices in helium II using micron-sized particles, revealing vortex interactions, networks, and turbulence, and comparing vortex density with theoretical predictions.

Contribution

It introduces a novel visualization method for superfluid vortices, enabling detailed study of vortex dynamics and turbulence in helium II.

Findings

Vortices are visualized using micron-sized hydrogen particles.

Vortex density matches Feynman's theoretical predictions.

First observation of superfluid turbulence with complex vortex networks.

Abstract

Matter at low temperatures exhibits unusual properties such as superfluidity, superconductivity, Bose-Einstein condensation, and supersolidity. These states display quantum mechanical behaviours at scales much larger than atomic dimensions. As in many phase transitions, defects can occur during the transition to the low temperature state. The study of these defects yields useful information about the nature of the transitions and of the macroscopic states themselves. When cooled below the lambda temperature (~2.172 K), liquid helium acquires superfluid properties, and the defects in the superfluid take the form of line vortices with quantized circulation. The formation of these vortices has been suggested as a model for cosmological structure formation. Here we visualize these superfluid (or quantized) vortices by suspending micron-sized solid particles of hydrogen in the fluid. The particles at low concentrations arrange themselves with nearly equal spacing along vortex lines. The number density of the vortex lines in a steadily rotating state compares well with Feynman's prediction. For the first time, it is possible to observe superfluid turbulence in which the superfluid vortices interact, and exist in networks with complex branching. Our method makes it possible to characterize the vortices during the transition across the lambda point and in the turbulent state itself.