Finite-size effects in plane layers of liquid 4He near the λ point

Abstract

Quantitative measurements of the liquid 4He density temperature dependence are taken near the λ point in a thin plane-parallel gap of thickness d=3.3×10 −5 cm with a well controlled geometry. Evidence is obtained that there are three effects contributing to the average helium density in the gap: (i) the shift of the λ transition temperature in the gap as compared to the bulk helium, (ii) the contribution to the average density from the inhomogeneity of the equilibrium order parameter distribution across the gap below T λ , (iii) the rounding of the logarithmic anomaly of the helium thermal expansion coefficient in the gap due to changes in the spectrum of the order parameter fluctuation in the direction across the gap. A comparison is given with predictions of the phenomenological Ψ-theory of superfluidity near the λ point as well as with those of scaling theory.