THE TRICRITICAL REGION FOR HELIUM MIXTURES IN 0.87 POROSITY AEROGEL

Citation
J. Beamish et M. Paetkau, THE TRICRITICAL REGION FOR HELIUM MIXTURES IN 0.87 POROSITY AEROGEL, Journal of low temperature physics, 113(5-6), 1998, pp. 1037-1042
Citations number
9
Categorie Soggetti
Physics, Applied
ISSN journal
00222291
Volume
113
Issue
5-6
Year of publication
1998
Pages
1037 - 1042
Database
ISI
SICI code
0022-2291(1998)113:5-6<1037:TTRFHM>2.0.ZU;2-S
Abstract
We have used ultrasonic velocity measurements to study He-3-He-4 mixtu res in aerogel with a porosity 0.87. The phase diagram resembles that of bulk mixtures, with a single transition for He-3-rich mixtures, in contrast to the detached phase separation curve seen in 0.98 porosity aerogel. A kink in the lambda line at a He-3 concentration of X-C = 0. 51 suggests that the phase separation line meets it at a tricritical p oint. We have measured the amount of superfluid which decouples both a t low temperature and close to the superfluid transition as functions of He-3 concentration. Each showed a sudden change at the concentratio n where the kink appeared in the lambda line, suggesting an abrupt cha nge in the morphology of the superfluid phase in the mixtures. Similar measurements were made for pure He-4 films on the same aerogel. We di scuss the nature of He-3-rich mixtures in aerogels based on these expe riments.