3 He in 99.5% Porous Aerogel at the Normal-Superfluid Transition (original) (raw)

Dissipation Mechanisms near the Superfluid He3 Transition in Aerogel

Physical Review Letters, 2004

We have investigated the dissipation (Q ÿ1 ) using the torsion pendulum technique for pure 3 He and 3 He-4 He mixtures in silica aerogel near the 3 He superfluid transition (T c ) in aerogel. With pure 3 He the Q ÿ1 decreases at the onset of superfluidity. When phase separated 3 He-4 He mixtures are introduced into the aerogel, the Q ÿ1 does not decrease as rapidly and eventually increases for the highest 4 He content. We provide a model for the related attenuation of transverse sound that takes into account elastic and inelastic scattering processes and exhibits a decrease in at T c .

Torsional oscillator studies of the superfluidity of 3He in aerogel

Physica B: Condensed Matter, 1998

We have made simultaneous torsional oscillator and transverse NMR measurements (at ∼ 165 kHz) on 3 He contained within aerogels with nominal densities of 1% and 2% of solid glass. The superfluid transition is seen simultaneously by both techniques and occurs at a temperature which agrees semi-quantitatively with that expected for homogeneous isotropic pair-breaking scattering of 3 He atoms by strands of silica. Values obtained for the superfluid density ρ s in the 2% sample are in reasonable agreement with those observed previously. Coupling of the torsional mode to a parasitic resonance prevented accurate determination of ρ s for the 1% aerogel. We have identified other resonances coupling to the torsional oscillations as sound modes within the helium/aerogel medium.

Coexistence of superfluid and solid helium in aerogel

Journal of Experimental and Theoretical Physics, 2010

The results of recent neutron scattering studies of solid helium in silica aerogel are discussed. Pre viously I.V. Kalinin et al., Pis'ma Zh. Éksp. Teor. Fiz. 87 (1), 743 (2008) [JETP Lett. 87 (1), 645 (2008)], we detected the existence of a superfluid phase in solid helium at a temperature below 0.6 K and a pressure of 51 bar, although, according to the phase diagram, helium should be in the solid state under these conditions. This work is a continuation of the above studies whose main goal was to examine the detected phenomenon and to establish basic parameters of the existence of a superfluid phase. We have determined the temperature of the superfluid transition from solid to superfluid helium, T C = 1.3 K, by analyzing experimental data. The superfluid phase excitation parameters (lifetime, intensity, and energy) have a temperature dependence sim ilar to that of bulk helium. The superfluid phase coexists with the solid phase in the entire measured temper ature range from T = 0.05 K to T C and is a nonequilibrium one and disappears at T C .

Models for Superfluid H3e in Aerogel

Physical Review Letters, 1998

Evidence of superfluidity of 3 He in 98%-porous aerogel has been found recently in two experiments. A microscopic model of the aerogel as a weakly inhomogeneous anisotropic scattering medium is shown to be in semi-quantitative agreement with experiments.

Thermal conductivity of superfluid 3He in aerogel

Physica B-condensed Matter, 2003

We report theoretical calculations of the thermal conductivity of superfluid 3 He impregnated into high-porosity aerogel and compare these results with available experimental data. r

Superfluid transition in superfluid3He in radially compressed aerogel

Journal of Physics: Conference Series, 2012

The Spin Supercurrent and Bose-Einstein condensation of magnons similar to an atomic BEC was observed in 1984 in superfluid 3 He-B. Recently we discovered 2 new types of BEC in superfluid 3 He in deformed aerogel. The orbital part of the wave function orients along the deformation and changes the magnon-magnon interaction. In some cases it forms a magnon trap. We can do it for 3 He-A by uniaxially compressing the aerogel along the magnetic field. The other BEC state was observed in 3 He-B in aerogel stretched along the magnetic field. Both states show all properties of magnon BEC. We have also observed a splitting of NMR lines near Tc, which seems to indicate the formation of a new phase of superfluid 3 He in aerogel. The latter looks like an analog of the 3 He-A1 phase with strongly enhanced magnetic field.

Superfluid phase stability of 3 He in axially anisotropic aerogel

Journal of Physics: Conference Series, 2009

Measurements of superfluid 3 He in 98% aerogel demonstrate the existence of a metastable A-like phase and a stable B -like phase. It has been suggested that the relative stability of these two phases is controlled by anisotropic quasiparticle scattering in the aerogel. Anisotropic scattering produced by axial compression of the aerogel has been predicted to stabilize the axial state of superfluid 3 He. To explore this possiblity, we used transverse acoustic impedance to map out the phase diagram of superfluid 3 He in a ∼ 98% porous silica aerogel subjected to 17% axial compression. We have previously shown that axial anisotropy in aerogel leads to optical birefringence and that optical cross-polarization studies can be used to characterize such anisotropy. Consequently, we have performed optical cross-polarization experiments to verify the presence and uniformity of the axial anisotropy in our aerogel sample. We find that uniform axial anisotropy introduced by 17% compression does not stabilize the A-like phase. We also find an increase in the supercooling of the A-like phase at lower pressure, indicating a modification to B -like phase nucleation in globally anisotropic aerogels.

Non-linear Mechanical Response of the A-like Phase of Superfluid 3He in Aerogel

Journal of Low Temperature Physics, 2007

We present measurements of the response of the Alike phase of superfluid 3 He in aerogel to an applied flow. The measurements are made using a cylindrical piece of 98% silica aerogel attached to a vibrating wire resonator. The resonator is immersed in superfluid 3 He at low temperatures and relatively high magnetic fields such that the aerogel confined superfluid is in the Alike phase, while the surrounding fluid is in the bulk B-phase. We observe a variety of interesting non-linear and hysteretic effects when the resonator is driven to higher velocities. We present some of our preliminary findings and speculate on their implications.

Evidence for Superfluid B Phase of 3He in Aerogel

Physical Review Letters, 1999

We have made simultaneous torsional oscillator and transverse cw NMR (at ∼ 165 kHz) studies of the superfluid phase of 3 He in aerogel glasses of 1% and 2% of solid density. NMR occurs over a range of frequency extending from the Larmor frequency to higher values, but strongly peaked at the Larmor value. This behaviour together with the magnetic field independence of the effective superfluid density provides convincing evidence for a B-phase state with ann texture, in our spherical geometry, governed by the same energetic considerations as for bulk superfluid 3 He-B. 67.57.Fg, 67.57.Lm, 67.57.Pq †