Transverse acoustic properties of the B-phase of superfluid helium three. Ph.D. Thesis

Thesis/Dissertation · Fri Dec 31 04:00:00 EST 1993

OSTI ID:121797

Moores, G F

In the past several decades, liquid helium three has been fertile ground for both theory and experiment. Nuclear magnetic resonance and ultrasound techniques have been important probes of the superfluid phases. NMR studies of (3)He-B in a strong magnetic field have shown a small frequency shift from the Larmor frequency of the normal phase. The authors present a theoretical calculation of this g-shift which involves the full field dependent susceptibility and order parameter in (3)He-B, and they compare the results to experiment. Studies of ultrasound in (3)He-B have focused primarily on longitudinal currents. Shear waves, or transverse current modes, are also expected to propagate in both normal and superfluid (3)He, but previous work has considered low frequency dynamics, where the mode is difficult to detect because its phase velocity is comparable to the incoherent quasiparticle background, and it disappears as the gap in the quasiparticle spectrum develops. In this thesis, a thorough examination of this mode in bulk superfluid (3)He-B is given. The author shows that the mode propagates with low attenuation for frequencies between the imaginary squashing mode frequency and the pair breaking edge at low temperatures where there are very few thermally excited quasiparticles. The transverse acoustic impedance is inherently dependent on the boundary conditions at the wall; the author considers (3)He-B in confined geometries near specular and diffuse walls before deriving microscopic boundary conditions to model a transversely oscillating wall.

• Research Organization: Northwestern Univ., Chicago, IL (United States)
• OSTI ID: 121797
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ACOUSTIC MEASUREMENTS
HELIUM 3 B
NUCLEAR MAGNETIC RESONANCE
PHASE VELOCITY
SUPERFLUIDITY
ULTRASONIC WAVES
WAVE PROPAGATION