POSSIBLE OBSERVATION OF THE SUBSTRATE STATE IN HE-3-HE-4 MIXTURE FILMS

We report on measurements of third sound in He-3-He-4 mixture films. The third sound velocity is measured as a function of temperature for He-4 thicknesses between 3.6 and 5.8 atomic layers (a.l.) and He-3 coverages up to 1.25 a.l. An anomaly in the third sound velocity is found around 200 mK for films with a He-4 thickness of less than 5 a.l. and He-3 coverages around 0.5 a.l. Comparison of the results is made with the model of Guyer and Miller and the calculations of Pavloff and Treiner [1, 2].