Mass coupling and Q−1ofimpurity−limitednormalQ^{-1} of impurity-limited normal ^3$He in a torsion pendulum

We present results of the $Q^{-1}$ and period shift, $\Delta P$, for $^3$He confined in a 98% nominal open aerogel on a torsion pendulum. The aerogel is compressed uniaxially by 10% along a direction aligned to the torsion pendulum axis and was grown within a 400 $\mu$m tall pancake (after compression) similar to an Andronikashvili geometry. The result is a high $Q$ pendulum able to resolve $Q^{-1}$ and mass coupling of the impurity-limited $^3$He over the whole temperature range. After measuring the empty cell background, we filled the cell above the critical point and observe a temperature dependent period shift, $\Delta P$, between 100 mK and 3 mK that is 2.9$$ of the period shift (after filling) at 100 mK. The $Q^{-1}$ due to the $^3$He decreases by an order of magnitude between 100 mK and 3 mK at a pressure of $0.14\pm0.03$ bar. We compare the observable quantities to the corresponding calculated $Q^{-1}$ and period shift for bulk $^3$He.Comment: 8 pages, 3 figure

Dissipation Mechanisms near the Superfluid 3He Transition in Aerogel

金沢大学理学部The dissipation mechanisms (Q-1) near the superfluid 3He transition in aerogel was investigated using the torsion pendulum technique. It was found that with pure 3He the Q-1 decerases at the onset of superfluidity. It was also found that when phase separated 3He-4He mixtures are introduced into the aerogel, the Q-1 does not decrease as rapidly and eventually increases for the highest 4He content. A model for the related attenuation of transverse sound α that takes into account elastic and inelastic scattering processes was also presented

Quantum Phase Transition of 3He in Aerogel at a Nonzero Pressure

金沢大学理学部We present evidence for a nonzero pressure, T ­ 0 superfluid phase transition of 3He in 98.2% open aerogel. Unlike bulk 3He which is a superfluid at T ­ 0 at all pressures (densities) between zero and the melting pressure, 3He in aerogel is not superfluid unless the 3He density exceeds a critical value rc. About 90% of the 3He added above rc contributes to the superfluid density. [S0031-9007(97)03585-0

Surface Roughness and Effective Stick-Slip Motion

The effect of random surface roughness on hydrodynamics of viscous incompressible liquid is discussed. Roughness-driven contributions to hydrodynamic flows, energy dissipation, and friction force are calculated in a wide range of parameters. When the hydrodynamic decay length (the viscous wave penetration depth) is larger than the size of random surface inhomogeneities, it is possible to replace a random rough surface by effective stick-slip boundary conditions on a flat surface with two constants: the stick-slip length and the renormalization of viscosity near the boundary. The stick-slip length and the renormalization coefficient are expressed explicitly via the correlation function of random surface inhomogeneities. The effective stick-slip length is always negative signifying the effective slow-down of the hydrodynamic flows by the rough surface (stick rather than slip motion). A simple hydrodynamic model is presented as an illustration of these general hydrodynamic results. The effective boundary parameters are analyzed numerically for Gaussian, power-law and exponentially decaying correlators with various indices. The maximum on the frequency dependence of the dissipation allows one to extract the correlation radius (characteristic size) of the surface inhomogeneities directly from, for example, experiments with torsional quartz oscillators.Comment: RevTeX4, 14 pages, 3 figure

VISCOSITY OF NORMAL AND SUPERFLUID HELIUM THREE

Nous avons mesuré la viscosité de la composante normale de l'3He dans les phases A et B, et dans le liquide de Fermi normal. Près de Tc, nous pouvons décrire la viscosité réduite avec l'équation (1 - η/ ηc) = A(l - T/Tc)1/2 - B(l - T/Tc). A l'aide des résultats applicables au liquide normal, nous avons calculé le temps de relaxation τ(0)T2 d'une quasi-particule dans l'état normal.The normal fluid viscosity has been measured in the A and B phases of 3He, as well as in the normal Fermi liquid. Near Tc we find that the reduced viscosity can be written in the form (1 - η/ ηc) = A(l - T/Tc)1/2 - B(1 - T/Tc) . Using the normal liquid results we have calculated the normal state quasiparticle relaxation time τ(0)T2