%0 Journal Article
%T Phase order in superfluid helium films
%A Steven T. Bramwell
%A Michael F. Faulkner
%A Peter C. W. Holdsworth
%A Andrea Taroni
%J Physics
%D 2015
%I arXiv
%R 10.1209/0295-5075/112/56003
%X 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.
%U http://arxiv.org/abs/1508.07773v1