Critical Casimir effect in dilute He-3-He-4 mixture films

Recently, we have found that He-4 films thin near the lambda point. Based o n our measurements, the thinning appears to be caused by the confinement of superfluid order parameter fluctuations in the films. The phenomenon of th e thinning is believed to be analogous to the Casimir effect in electromagn etism where the confinement of electromagnetic fluctuations causes the vacu um layer that separates two metal plates to thin. In this paper, we report the result of an experiment extending our previous study to He-3-He-4 mixtu re films. Thinning is found near the new lambda points and the characterist ics of the thinning are similar to that found in pure He-4 films. (C) 2000 Elsevier Science B.V. All rights reserved.