The use of 3He NMR as a probe of the nature of the 4He solid/superfluid interface

When liquid helium is in contact with a graphite surface, and the pressure of the liquid is increased toward the bulk solidification pressure, then solid helium will grow epitaxially, layer by layer, on the graphite. At temperatures near 1 K the layer growth is as one would expect, but at temperatures below .9 K an unexpected two-stage layering transition appears. When 3He is added to the system, it preferentially resides at the solid/liquid interface and has significant effects on the interface behavior. In the past the authors have obtained quantitative measurements of these effect with an acoustic technique. Currently they are attempting to use an NMR technique, which monitors the diffusion of the 3He, as a probe of the interface effects. Currents results will be presented