Measurements of vortex diffusivity in 2D superfluid /sup 4/He

Thesis/Dissertation · Thu Jan 01 04:00:00 EST 1987

OSTI ID:5235599

Volz, S M

The author measured for the first time, the characteristics of vortex-induced superfluid-flow dissipation at temperatures well below the Kosterlitz-Thouless superfluid transition temperature. Studies were with films of coverage .25 < sigma/sub s/ < 1.9 superfluid atomic layers and with .55 < T/sub KT/ < 1.9/sup 0/K. A third sound resonator combined is used with a new detection technique that allows measurements and the vortex dynamics in the superfluid. Using a model developed by Gillis, et al., the vortex-induced dissipation is fitted to the data using as adjustable parameters the vortex diffusivity D and the free vortex creation time tau/sub free/. D was found to be dependent on superfluid thickness and temperature (for 90 mK < T < 600mK), but to be independent of superfluid flow velocity, frequency of the oscilating velocity field and, with the exception of the thinnest film on Neon, of the /sup 4/He-substrate van der Waals strength. However, the free-vortex creation time tau/sub free/ was found to be a strong function of the van der Waals strength. Measurements on Ar yield tau/sub free/ T/sup -1.3/ while on Ne tau/sub free/ approx. T/sup -5.2/. For the thinnest film on Ne (sigma/sub s/ = .60 layers) D is anomalously large yet temperature-independent, and tau/sub free/ is immeasurably large. It is postulated that surface roughness may affect the diffusivity of this thin film

• Research Organization: Illinois Univ., Urbana (USA)
• OSTI ID: 5235599
• Country of Publication: United States
• Language: English

Related Subjects

640450* -- Fluid Physics-- Superfluidity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
DIFFUSION
EVEN-EVEN NUCLEI
FILMS
FLUID FLOW
HELIUM 4
HELIUM ISOTOPES
ISOTOPES
LIGHT NUCLEI
NUCLEI
STABLE ISOTOPES
SUPERFLUIDITY
THIN FILMS
ULTRALOW TEMPERATURE
VAN DER WAALS FORCES
VELOCITY
VORTEX FLOW