Superfluid helium four in disordered porous media

Thesis/Dissertation · Sat Dec 31 23:00:00 EST 1988

OSTI ID:5754926

Blum, K I

This work describes experiments on the behavior of superfluid {sup 4}He in disordered porous materials. The bulk of the work focuses on the normal liquid to superfluid transition that takes place at finite temperatures; a final chapter deals with the quantum onset transition, whose presence at T = O and nature are inferred from low coverage superfluid films. There is an extended discussion of the porous media themselves and the difficulties of determining their structure. The critical behavior of the superfluid is found to be profoundly affected in porous silica gels. This is in contrast to earlier experiments which found that in porous Vycor glass the exponent remained identical to that governing the bulk transition, within experimental uncertainty (Bishop 1981). In these new materials, porous silica gels with 60% and 94% porosity, the superfluid density exponent measured with a mechanical torsional pendulum was clearly shifted to higher values. Since the superfluid helium is sensitive to the spatial arrangement of the silica skeleton, this work holds out the hope of a novel means to characterize porous media. It has been generally observed that on any substrate, for coverages below roughly two atomic layers of helium, superfluidity is never seen. Above this onset coverage, the extrapolated superfluid density at T = O has been found to vary linearly with the coverage, save for a small region just above onset. The experiments on {sup 4}He films coating packed carbon black particles show a large enhancement of the non-linear regime near the onset coverage. Preliminary date are in reasonable agreement with recent theory on the quantum onset transition of superfluidity in random media.

• Research Organization: Cornell Univ., Ithaca, NY (USA)
• OSTI ID: 5754926
• Country of Publication: United States
• Language: English

Related Subjects

640450* -- Fluid Physics-- Superfluidity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
COLLOIDS
DENSITY
DISPERSIONS
EVEN-EVEN NUCLEI
FLUIDS
GELS
HELIUM 4
HELIUM II
HELIUM ISOTOPES
ISOTOPES
LIGHT NUCLEI
MATERIALS
NONLINEAR PROBLEMS
NUCLEI
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
POROSITY
POROUS MATERIALS
QUANTUM FLUIDS
STABLE ISOTOPES
SUPERFLUIDITY