HELIUM MIXTURES ON WEAK BINDING SUBSTRATES

It has been recently proposed that He-3 bound states may exist in the first non solid layer of liquid helium near a substrate [N. Pavloff and J. Treiner, J. Low Temp. Phys. 83, 331 (1991)]. Detailed calculations show that for weak binding substrates on which helium remains liquid, the energy of this substrate state epsilon(s) is in the range -4 to -5.5 K, whereas for stronger substrates on which one or two layers solidify, epsilon(s) is larger than the energy of a He-3 atom in bulk He-4 (-2.8 K). As a special case, we find that He-3 atoms can be bound at the He-4 solid-liquid interface, with a binding energy of approximately 3 K with respect to bulk. Experiments able to test these predictions are proposed.