HE-3 EFFECTIVE-MASS IN HELIUM MIXTURES IN AEROGEL

The most direct method to determine the superfluid fraction of liquid helium is to measure the decoupling of the superfluid from an oscillat ing substrate. The classic example of this method is the torsional osc illator, but quartz microbalance and ultrasonic velocity measurements are also sensitive to mass decoupling. Measurements of helium mixtures in aerogel have seen a decoupling effect when dilute mixtures (low He -3 concentration, X) phase separate at low temperatures. The decouplin g can be understood in terms of a hydrodynamic description of the He-3 effective mass and we can determine the effective mass from our exper imental data. A similar effect should be seen in phase separation of 2 -D helium film mixtures.