Healing length near theλpoint in liquid helium

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 i i, 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 λ point at $T_{\lambda }$. In bulk He i i the results confirm a previous measurement of the healing length a(T)=(0.094±0.002)${\epsilon }^{\mathrm{-}2/3}$ nm, where ε=‖1-T/$T_{\lambda }$‖. In bulk He i the measurements suggest that the viscosity exhibits healing above $T_{\lambda }$ near a solid wall with a similar healing length as in He i i. 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.