Thin $$^4$$He Films on Alkali Substrates: Where Do $$^3$$He Atoms Bind?

Abstract

The possible occurrence of bound states of $$^3$$ He atoms in the vicinity of a weakly attractive substrate coated with a thin superfluid $$^4$$ He film is investigated by first principle computer simulations. No evidence is seen of such bound states, even in the case of the weakest substrate, i.e., Cs; a single $$^3$$ He atom always binds to the free $$^4$$ He surface, regardless of the thickness of the $$^4$$ He film. A comparison of $$^4$$ He density profiles computed in this work with those yielded by the Density Functional approach that led to the prediction of $$^3$$ He bound states near the substrate shows that the latter may not have afforded a sufficiently accurate structural description of the adsorbed $$^4$$ He film.