Superfluid transition in superfluid3He in radially compressed aerogel (original) (raw)

Bose-Einstein Condensation of Magnons in Superfluid 3He

Journal of Low Temperature Physics, 2008

The possibility of Bose-Einstein condensation of excitations has been discussed for a long time. The phenomenon of the phase-coherent precession of magnetization in superfluid 3 He and the related effects of spin superfluidity are based on the true Bose-Einstein condensation of magnons. Several different states of coherent precession has been observed in 3 He-B: homogeneously precessing domain (HPD); persistent signal formed by Q-balls at very low temperatures; coherent precession with fractional magnetization; and two new modes of the coherent precession in compressed aerogel. In compressed aerogel the coherent precession has been also found in 3 He-A. Here we demonstrate that all these cases are examples of a Bose-Einstein condensation of magnons, with the magnon interaction term in the Gross-Pitaevskii equation being provided by different types of spin-orbit coupling in the background of the coherent precession.

Magnetic Distortion of the B-like Phase of Superfluid 3He Confined in Aerogel

Journal of Low Temperature Physics, 2008

We present measurements of the response of the B-like 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 16 bar pressure and at low temperatures. A variable magnetic field is applied such that the aerogel-confined superfluid may exist in the Alike or B-like phase, while the surrounding fluid is always in the bulk B-phase. The resonator response reveals a velocity dependence of the inferred aerogel-confined superfluid fraction. We discuss measurements of the temperature and magnetic field dependence of the response in the B-like phase. We find a significant field dependence indicating a strong magnetic distortion of the B-like phase order parameter.

Magnetic Field Dependence of the A-like to B-like Transition of Superfluid 3He in Aerogel

Journal of Low Temperature Physics, 2010

Longitudinal ultrasound attenuation of superfluid 3 He in 98% aerogel has been measured at 33 bar and 6.22 MHz in the presence of magnetic fields up to 4.44 kG. The A-like to B-like (A-B like) phase transition in aerogel was identified by a rounded jump in attenuation while sweeping the temperature at a fixed magnetic field perpendicular to the direction of sound propagation. The suppression of the B-like phase was monitored as the magnetic field increased until the A-like phase region extended below our lowest attainable temperature (0.2 mK) at the highest field. In addition, the attenuation in the metastable A-like phase that appears when cooling in zero magnetic field was almost identical to the values observed in the A-like phase in high magnetic field.

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 †

Non-ground-state Bose-Einstein condensates of magnons in superfluid 3He-B

2010

Long-lived coherent spin precession of 3He-B at low temperatures around 0.2 Tc is a manifestation of Bose-Einstein condensation of spin-wave excitations or magnons in a magnetic trap which is formed by the order-parameter texture and can be manipulated experimentally. When the number of magnons increases, the orbital texture reorients under the influence of the spin-orbit interaction and the profile of the trap gradually changes from harmonic to a square well, with walls almost impenetrable to magnons. This is the first experimental example of Bose condensation in a box. By selective rf pumping the trap can be populated with a ground-state condensate or one at any of the excited energy levels. In the latter case the ground state is simultaneously populated by relaxation from the exited level, forming a system of two coexisting condensates.

Spin vortex in magnon BEC of superfluid 3He–B

Physica C: Superconductivity, 2008

The phenomenon of the spontaneous phase-coherent precession of magnetization in superfluid 3 He and the related effects of spin superfluidity are based on the true Bose-Einstein condensation of magnons. Several different magnon BEC states have been observed: homogeneously precessing domain (HPD); BEC condensation in the spin-orbit potential trap (Q-balls); coherent precession with fractional magnetization; and two modes of the coherent precession in squeezed aerogel. The spin superfluidity effects, like spin Josephson phenomena, spin current vortices, spin phase slippage, long distance magnetization transport by spin supercurrents have been observed.

Magnon BEC and Spin Superfluidity: a 3He primer

Bose-Einstein condensation (BEC) is a quantum phenomenon of formation of the collective quantum state, in which the macroscopic number of particles occupies the lowest energy state and thus is governed by a single wave function. Here we highlight the BEC in a magnetic subsystem -- the BEC of magnons, elementary magnetic excitations. Magnon BEC is manifested as the spontaneously emerging state of the precessing spins, in which all spins precess with the same frequency and phase even in the inhomogeneous magnetic field. We consider this phenomenon on example of spin precession in superfluid phases of 3^33He. The magnon BEC in these phases has all the properties of spin superfluidity. The states of the phase-coherent precession belong to the class of the coherent quantum states, which manifest themselves by superfluidity, superconductivity, quantum Hall effect, Josephson effect and many other macroscopic quantum phenomena.

Strong Orientational Effect of Stretched Aerogel on the He3 Order Parameter

Physical Review Letters, 2008

Deformation of aerogel strongly modifies the orientation of the order parameter of superfluid 3 He confined in aerogel. We used a radial squeezing of aerogel to keep the orbital angular momentum of the 3 He Cooper pairs in the plane perpendicular to the magnetic field. We did not find strong evidence for a "polar" phase, with a nodal line along the equator of the Fermi surface, predicted to occur at large radial squeezing. Instead we observed 3 He-A with a clear experimental evidence of the destruction of the long-range order by random anisotropy -the Larkin-Imry-Ma effect. In 3 He-B we observed and identified new modes of NMR, which are impossible to obtain in bulk 3 He-B. One of these modes is characterized by a repulsive interaction between magnons, which is suitable for the magnon Bose-Einstein condensation (BEC).

Impurity effects on the A1-A2 splitting of superfluid 3He in aerogel

Physical Review B, 2003

When liquid 3 He is impregnated into silica aerogel a solid-like layer of 3 He atoms coats the silica structure. The surface 3 He is in fast exchange with the liquid on NMR time scales. The exchange coupling of liquid 3 He quasiparticles with the localized 3 He spins modifies the scattering of 3 He quasiparticles by the aerogel structure. In a magnetic field the polarization of the solid spins gives rise to a splitting of the scattering cross section of for ''up'' vs ''down'' spin quasiparticles, relative to the polarization of the solid 3 He. We discuss this effect, as well as the effects of nonmagnetic scattering, in the context of a possible splitting of the superfluid transition for ↑↑ vs ↓↓ Cooper pairs for superfluid 3 He in aerogel, analogous to the A 1 -A 2 splitting in bulk 3 He. Comparison with the existing measurements of T c for BϽ5 kG, which shows no evidence of the A 1 -A 2 splitting, suggests a liquid-solid exchange coupling of order JӍ0.1 mK. Measurements at higher fields, B տ20 kG, should saturate the polarization of the solid 3 He and reveal the A 1 -A 2 splitting.