The transverse acoustic impedance of He II

Journal Article · Tue Jan 31 23:00:00 EST 1984 · J. Low Temp. Phys.; (United States)

DOI:https://doi.org/10.1007/BF00683280· OSTI ID:6761189

Lea, M J; Fozooni, P; Retz, P W

The complex shear acoustic impedance of liquid He II has been measured at frequencies f( = ..omega../2..pi..) of 20.5, 34.1, and 47.8 MHz from 30 mK to the lambda-point T/sub lambda/ (2.176 K). The impedance Z was found from the temperature dependence of the quality factor and the resonant frequency of a thickness shear mode quartz crystal resonator immersed in the liquid. The relationship for a hydrodynamic viscous liquid Z(T) = (1-i)(..pi..fetap/sub n/)/sup 1/2/ was used to measure the temperature dependence of the viscosity eta(T) using tabulated values of the normal fluid density rho/sub n/ (T). Deviations from hydrodynamic behavior occurred when the viscous penetration depth was less than the superfluid healing length, the phonon mean free path, and the roton mean free path. Near the lambda-point, Z(T)/Z(T/sub lambda/) was frequency dependent and a value for the superfluid healing length a = (0.10 +- 0.01)epsilon/sup -2/3/ nm was found, where epsilon = (T/sub lambda/-T)/T/sub lambda/. The effects of van der Waals forces near the crystal surface were also observed and a layer model was used to interpret the measurements. Below 1.8 K only rotons contribute significantly to Z and we determined the roton relaxation time as tau/sub r/ = 8.5 x 10/sup -14/T/sup -1/3/ exp (8.65/T) sec. Below 1.2 K, ..omega..tau/sub r/>1 and we investigated the breakdown of hydrodynamics in this region. For T<0.6 K the resonant frequency of the crystals decreased by ..delta..f/f = 2 x 10/sup 77/, but the origin of this effect is not yet known.

• Research Organization: Department of Physics, Bedford College, University of London, London, England
• OSTI ID: 6761189
• Journal Information: J. Low Temp. Phys.; (United States), Journal Name: J. Low Temp. Phys.; (United States) Vol. 54:3; ISSN JLTPA
• Country of Publication: United States
• Language: English

Related Subjects

640450* -- Fluid Physics-- Superfluidity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ACOUSTICS
DATA
ELECTRONIC EQUIPMENT
EQUIPMENT
EVEN-EVEN NUCLEI
EXPERIMENTAL DATA
FLUIDS
FREQUENCY RANGE
HELIUM 4
HELIUM II
HELIUM ISOTOPES
IMPEDANCE
INFORMATION
ISOTOPES
LIGHT NUCLEI
MEAN FREE PATH
MHZ RANGE
MHZ RANGE 01-100
NUCLEI
NUMERICAL DATA
PHONONS
QUALITY FACTOR
QUANTUM FLUIDS
QUASI PARTICLES
RESONATORS
ROTONS
STABLE ISOTOPES
TEMPERATURE DEPENDENCE
ULTRALOW TEMPERATURE
VISCOSITY