ANOMALOUS WETTING OF HELIUM ON CESIUM

We report studies of the anomalous wetting of a cesium substrate by a liquid-helium film by means of the technique of third sound. In an apparatus which incorporates both glass and cesium substrates, we observe third sound to propagate across cesium for helium films such that the film thickness on glass is d(g) greater-than-or-equal-to 11.5 layers. For d(g) less-than-or-equal-to 9 layers, third sound does not propagate across the cesium substrate. The transition region is hysteretic as a function of the amount of helium in the experimental cell.