Attenuation and dispersion of first sound near the superfluid transition of pressurized /sup 4/He

Journal Article · Sat Oct 01 04:00:00 EDT 1977 · Phys. Rev., B; (United States)

DOI:https://doi.org/10.1103/PhysRevB.16.3133· OSTI ID:7082574

Carey, R; Buchal, C; Pobell, F

The attenuation ..cap alpha.., the velocity u, and the dispersion D = u (..omega..) - u (0) of first sound have been measured in pressurized liquid /sup 4/He (P = 0.06, 5.01, 9.21, 15.24, 20.38, 25.46, 29.33 bar) near the superfluid transition. The frequency range was 4.6 kHz < or = ..omega../2..pi.. < or = 1.0 MHz, the temperature range was 1 ..mu..K < or = vertical-bar T - T/sub lambda/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 at constant T/sub lambda ts-tsT/are only weakly pressure dependent. 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/sub R/ of the relaxation process and the amplitude tau'/sub 0/ of the relaxation time tau' = tau'/sub 0/t/sup -x prime/are independent of pressure to within 10%; (t = vertical-barT - T/sub lambda tsvertical-barts/Tlambda/). The latter result seems to be inconsistent with the pressure independence of the correlation-length amplitude xi'/sub 0/ = 1.0 +- 0.05 A (which was confirmed in this work), and the known pressure dependence of the amplitude u/sub 2,0/ of second-sound velocity, if the relation tau' = xi'/u/sub 2/ is correct. For T > T/sub lambda/where only critical fluctuations contribute, our absorption and dispersion data for all ..omega.. and P can be scaled with functions of ..omega..tau for 10/sup 2/ > ..omega..tau > 10/sup -2/. This scaling analysis shows that the time tau characterizing the critical order-parameter fluctuations at T > T/sub lambda/has the same temperature and pressure 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

• Research Organization: Institut fuer Festkoerperforschung, Kernforschungsanlage Juelich, 517 Juelich, West Germany
• OSTI ID: 7082574
• Journal Information: Phys. Rev., B; (United States), Journal Name: Phys. Rev., B; (United States) Vol. 16:7; ISSN PLRBA
• Country of Publication: United States
• Language: English

Related Subjects

640450* -- Fluid Physics-- Superfluidity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION
DISPERSION RELATIONS
EVEN-EVEN NUCLEI
FREQUENCY RANGE
HELIUM 4
HELIUM ISOTOPES
ISOTOPES
KHZ RANGE
KHZ RANGE 01-100
KHZ RANGE 100-1000
LIGHT NUCLEI
NUCLEI
PHASE TRANSFORMATIONS
SOUND WAVES
STABLE ISOTOPES
ULTRALOW TEMPERATURE
VELOCITY