Magnetic relaxation in superfluid<Superscript>3</Superscript>He-B at very low temperatures

Main properties of the spin supercurrents and coherent precession of magnetization in the superfluid³He-B in hydrodynamic regime seem to be very well understood now. But recently surprisingly new unpredicted phenomena such as, for example, “catastrophic” relaxation, persistent spin precession, very strong magnetic relaxation, etc., have been observed in³He-B at ultralow temperatures in so-called non-hydrodynamic regime using both pulse and cw-NMR techniques. This paper deals with some of these new phenomena (a “linear term” in magnetic relaxation and a reduction of magnetization of coherent precession with magnetic field gradient) observed by cw-NMR technique, compares these results with new effects found by pulse NMR and speculates about the nature of these new phenomena.     

New non-Goldstone collective mode of BEC of magnons in superfluid 3He-B

Bose-Einstein condensation of magnons in superfluid 3He-B is experimentally manifested by various states where coherent spin precession is established spontaneously, even in nonhomogeneous magnetic fields. Once such a condensate with coherent spin precession is created, it occupies the state with minimal energy, the ground state. The application of an additional magnetic field to that condensate may cause its deflection from the energy minimum and the condensate responds by creating collective gapless oscillations known as Goldstone modes. This Letter reports the experimental observation of a new (non-)Goldstone mode, which can be viewed as an additional NMR mode of condensed magnons in a rotating frame of reference.     

Spin precession waves in superfluid 3He-B

Spin precession waves of homogeneously precessing domains (HPD) in superfluid 3He-B have been studied at 11 bars and temperatures down to 0.45T(c). The waves were excited by an alternating longitudinal magnetic field with an axial symmetry, applied as a small perturbation ranging from 1 nT up to a few micro T. When the spin precession wave is excited, two nuclear magnetic resonances simultaneously coexist: first, the high frequency resonance used for excitation of the HPD, and, second, the low-frequency resonance of the HPD wave mode. We report the first experimental evidence of the nonlinear behavior of low-frequency precession spin wave modes of the continuously maintained HPD.     

Interfacial energy of the superfluid 3He a-B phase interface in the zero-temperature limit

We have measured the surface energy of the interface between the A and B phases of superfluid 3He in the low temperature limit at zero pressure. Using a shaped magnetic field, we control the passage of the phase boundary through a small aperture. We obtain the interphase surface energy from the over- or undermagnetization required to force the interface through the aperture in both directions, yielding values of the surface tension and the interfacial contact angle. This is the first measurement of the interfacial energy in high magnetic fields and in the zero-temperature limit.     

Primary and secondary nucleation of the transition between the A and B phases of superfluid 3He

We have studied nucleation in superfluid 3He across the A-B phase transition driven by a magnetic field, in a controllable environment at very low temperatures. Both B-->A and A-->B secondary nucleation appear to be governed by the survival of pockets of the new phase trapped at surfaces. We find that, at fields near B(AB), primary A-->B nucleation cannot be triggered by ionizing or neutron irradiation even at very high intensities. In our cell primary A-->B nucleation can only be triggered externally by mild mechanical shock.     

Physiological, biochemical and molecular characteristics of cryopreserved Hypericum perforatum L. shoot tips

Hypericum perforatum L. in vitro cultured shoot tips were characterised at the physiological, biochemical and molecular levels following recovery from cryogenic treatment using the plant vitrification solutions PVS2 and PVS3. This comparative study revealed an increase in recovery and regrowth of explants cryoprotected with PVS3. Among the physiological markers only lipid peroxidation in the regenerants treated with PVS2 significantly increased indicating membrane damage. Genotype-specific interactions were found in most characteristics studied, with some variation detected within control and cryopreserved samples. Analyses of metabolite biosynthesis and genetic stability showed no significant differences in hypericin content, RAPD and minisatellite amplification profiles between PVS2- and PVS3-treated explants. This study demonstrates and discusses the criteria selective for PVS3 to improve the cryopreservation of H. perforatum L.     

The thermodynamics of the A–B transition in superfluid He as a probe of the A-phase gap node geometry

We have used a magnetic field gradient to stabilise the phase boundary between the A- and B-phases of superfluid ³He inside a quasiparticle black body radiator down to 146 μK. The radiator technique enables us to measure very accurately the density of quasiparticle excitations and therefore the temperature of the B-phase inside the radiator. As we ramp the field through the transition we can observe the cooling (warming) effect when the volume of A-phase is increased (decreased). From these measurements we deduce the temperature dependence of the latent heat, which provides the lowest temperature verification yet of the existence of nodes in the A-phase order parameter.     

Coherently Precessing Spin Structure in 3He-B High-Resolution Quantum Amplifier

We present results of the study of surface oscillation modes of coherently precessing nuclear spins in the superfluid ³He-B known as a homogeneously precessing domain (HPD). HPD represents the first macroscopic experimental manifestation of magnetic superfluidity phenomenon. The measurements showed that HPD is extremely sensitive to longitudinal perturbations and it behaves as tuned (by magnetic field gradient) quantum amplifier that allows to measure very small changes of magnetic field with very high relative resolution, of the order of 10^-7.