A very low-frequency measurement of the zeta exponent of helium in aerogel

The inertial mass of a long cylinder of aerogel, moving in He-II, is very s ensitive to the helium superfluid density both inside and outside the aerog el, and involves conversion of the superfluid components into one another. The very low resonance frequency of a simple pendulum built with the cylind er gives access to the superfluid density inside the aerogel. An accuracy o f 10(-4) is obtained. For three tested samples, the exponent xi is found la rger than the bulk value. (C) 2000 Elsevier Science B.V. All rights reserve d.