Healing length near the lambda point in liquid helium.

Abstract

Viscous shear waves have been used to probe the spatial variation and healing of the viscosity and superfluid density near a solid wall in bulk He i, bulk He ii, and in saturated superfluid films with thicknesses from 14 to 24 nm. The shear waves were generated at 20 and 34 MHz with an AT-cut quartz crystal resonator, and the transverse-acoustic impedance of the helium was measured at temperatures T close to the \ensuremath{\lambda} point at ${T}_{\ensuremath{\lambda}}$. In bulk He ii the results confirm a previous measurement of the healing length a(T)=(0.094\ifmmode\pm\else\textpm\fi{}0.002)${\ensuremath{\epsilon}}^{\mathrm{\ensuremath{-}}2/3}$ nm, where \ensuremath{\epsilon}=\ensuremath{\Vert}1-T/${T}_{\ensuremath{\lambda}}$\ensuremath{\Vert}. In bulk He i the measurements suggest that the viscosity exhibits healing above ${T}_{\ensuremath{\lambda}}$ near a solid wall with a similar healing length as in He ii. Healing effects were observed below the superfluid transition temperature in the films and are also described by the same healing length as in the bulk liquid.