Transverse acoustic impedance of dilute solutions of /sup 3/He in superfluid /sup 4/He
The transverse acoustic impedance Z = R - iX of dilute solutions of /sup 3/He in superfluid /sup 4/He has been measured at a frequency (omega/2..pi..) of 20.5 MHz at temperatures T from 30 mK to the lambda transition at T/sub lambda/. The /sup 3/He concentrations studied were c = 0.014, 0.031, 0.053, 0.060, and 0.092 below 1 K, though c decreased slightly near the lambda point. The impedance was found from the temperature dependence of the quality factor and the resonant frequency of an AT-cut quartz crystal resonator immersed in the liquid. Below 1 K, Z is due to the Fermi gas of /sup 3/He quasiparticles, and in the collisionless limit, omega tau >> 1 (tau is a relaxation time), R remains constant while X goes to zero. Measurements of R(c, T) and X(c, T) were analyzed to determine the momentum accommodation coefficient ..cap alpha..(c, T) and tau(c, T). The relaxation times were in good agreement with previous work, while ..cap alpha..(c, T) was independent of c, but increased from 0.29 +/- 0.03 below 0.1 K to 1.0 +/- 0.1 above 0.8 K. Various mechanisms are suggested to explain this. Between 1.0 and 1.5 K the /sup 3/He quasiparticles and the thermally excited rotons are in the hydrodynamic region, omega tau << 1. Values of the total viscosity eta(c, T) were obtained and analyzed to give the /sup 3/He gas viscosity and the /sup 3/He-/sup 3/He and roton-/sup 3/He scattering rates, both of which were energy-dependent. The superfluid healing length a was also measured. Near the lambda point they found a = (0.1 +/- 0.03)epsilon/sup -2/3/ nm, where epsilon = 1 - T/T/sub lambda/, proportional to the phase coherence length zeta. Their data are consistent with the hypothesis that zeta rho/sub s/T is a universal constant for superfluid dilute solutions, where rho/sub s/ is the superfluid density. Between 1.0 and 1.8 K they found that a(c, T) was comparable to measurements in /sup 3/He-/sup 3/He films.
- Research Organization:
- Univ. of London, Egham, England
- OSTI ID:
- 6060341
- Journal Information:
- J. Low Temp. Phys.; (United States), Journal Name: J. Low Temp. Phys.; (United States) Vol. 66:5-6; ISSN JLTPA
- Country of Publication:
- United States
- Language:
- English
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SUPERCONDUCTIVITY AND SUPERFLUIDITY
ACOUSTICS
BINARY MIXTURES
CHALCOGENIDES
DENSITY
DISPERSIONS
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ENERGY DEPENDENCE
ENERGY GAP
ENERGY-LEVEL TRANSITIONS
EQUIPMENT
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MIXTURES
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OXIDES
OXYGEN COMPOUNDS
PHONONS
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QUARTZ
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SILICON COMPOUNDS
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