Attenuation and dispersion of first sound near the superfluid transition of /sup 3/He-/sup 4/He mixtures

Journal Article · Sun Aug 01 04:00:00 EDT 1976 · Phys. Rev., B; (United States)

DOI:https://doi.org/10.1103/PhysRevB.14.1103· OSTI ID:7268577

Buchal, C; Pobell, F

The attenuation ..cap alpha.., the velocity u, and the dispersion D = u (..omega..) - u (0) of first sound have been determined in /sup 3/He-/sup 4/He mixtures (molar /sup 3/He concentrations X/sub 3/ = 0, 0.070, 0.194, 0.377, and 0.517) at frequencies 2.3 < or = ..omega../2..pi.. < or = 627 kHz, and in the termperature range 1 ..mu..K < or = absolute value (T - T/sub lambda/ ) < or = 10 mK. From the measured velocities we calculate the thermodynamic velocity u (0), as well as (partialS/partialP)/sub lambda/ and (partialV/partialP)/sub lambda/. The attenuation and the dispersion are considerably reduced when the /sup 3/He concentration is increased. They are interpreted as arising from a relaxation process occurring only below T/sub lambda/, and a fluctuation process occurring on both sides of the lambda transition. Both contributions have about equal strength. The strength A/subR/ of the relaxation process decreases by more than three orders of magnitude with increasing X/sub 3/ in our concentration range. Using the obtained relaxation time tau' = tau'/sub 0/t/sup -//subx//sup prime/ (with t = absolute value( T - T/sub lambda/ )/T/sub lambda/), and published data for the correlation length xi', and for the second-sound velocity u/sub 2/, we find tau' = xi'/u/sub 2/ for T < /T/sub lambda/. The amplitude tau'/sub 0/ increases more than one order of magnitude with increasing X/sub 3/ in the investigated concentration range. For T > T/sub lambda/, our absorption and dispersion data for all ..omega.. and X/sub 3/ can be scaled with functions of ..omega..tau over four decades of ..omega..tau. This scaling analysis shows that the time tau characterizing the critical attenuation and dispersion at T < T/sub lambda/ has the same temperature and concentration dependence as the relaxation time tau' at T < T/sub lambda/; these two times differ at most by a constant multiplicative factor. Below T/sub lambda/, the data are represented by the sum of the contribution represented by the scaling function plus the contribution from order parameter relaxation. (AIP)

• Research Organization: Institut fur Festkorperforschung, Kernforschungsanlage Julich, 517 Julich, West Germany
• OSTI ID: 7268577
• Journal Information: Phys. Rev., B; (United States), Journal Name: Phys. Rev., B; (United States) Vol. 14:3; ISSN PLRBA
• Country of Publication: United States
• Language: English

Related Subjects

640450* -- Fluid Physics-- Superfluidity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ATTENUATION
DISPERSION RELATIONS
DISPERSIONS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HELIUM 3
HELIUM 4
HELIUM ISOTOPES
ISOTOPES
LIGHT NUCLEI
MIXTURES
NUCLEI
SOUND WAVES
STABLE ISOTOPES
SUPERFLUIDITY
VELOCITY