Phase order in superfluid helium films

TL;DR

This paper analyzes superfluid helium films to estimate a finite-size phase order parameter, revealing a BKT phase transition characterized by universal scaling and providing insights into two-dimensional Bose fluids.

Contribution

It introduces a method to estimate the phase order parameter in helium films and demonstrates universal scaling near the BKT transition, linking experimental data to critical phenomena.

Findings

The phase order parameter evolves with a specific critical exponent.

Universal scaling collapse observed in helium and ferromagnetic films.

Experimental data supports the BKT phase transition framework.

Abstract

Classic experimental data on helium films are transformed to estimate a finite-size phase order parameter that measures the thermal degradation of the condensate fraction in the two-dimensional superfluid. The order parameter is found to evolve thermally with the exponent $\beta = 3 \pi^2/128$, a characteristic, in analogous magnetic systems, of the Berezinskii-Kosterlitz-Thouless (BKT) phase transition. Universal scaling near the BKT fixed point generates a collapse of experimental data on helium and ferromagnetic films, and implies new experiments and theoretical protocols to explore the phase order. These results give a striking example of experimental finite-size scaling in a critical system that is broadly relevant to two-dimensional Bose fluids.