3He impurities on the bulk surface of liquid4He: Possible existence of excited states

Abstract

We study, using a density-functional approach, the properties of the two-dimensional system formed by3He atoms on the surface of liquid4He, as a function of3He coverageN s , at zero temperature. We find several types of surface states accessible to the3He atoms. For small values ofN s , the surface tension σ is, as expected, linear inN 2 . For a coverage of about half a monolayer, a new type of surface state starts being occupied, and this produces a change in the slope of σ as a function ofN 2 and, more clearly, a step in the surface specific heat, which increases by a factor of almost two. Another step is predicted to occur for a coverage of ∼1.3 monolayer. Existing data are compatible with this structure of surface states but are not numerous enough to prove or disprove the existence of steps.