Orientation effect on superfluid 3He in anisotropic aerogel

Kunimatsu, T.; Sato, Toshihiro; Izumina, K.; Matsubara, Atsushi; Sasaki, Yutaka; Kubota, Minoru; Ishikawa, Osamu; Mizusaki, T.; Bunkov, Yu. M.

doi:10.1134/s0021364007150143

Cited by 65 publications

(82 citation statements)

References 16 publications

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“…In the context of identification of the superfluid state we have discussed the NMR frequency shifts and spectra expected for the A and B-phases. In some cases, such as the 99.3% aerogel samples of Baumgardner et al 58) the spectrum is very broad; in other cases 8,14,17,64) much less so. In the first NMR experiments, Sprague et al 8) took data only on warming.…”

Section: Nmr and Magnetizationmentioning

confidence: 99%

“…This was first seen by Barker et al 61) in a 98% aerogel and subsequently by many other groups. 14,29,58,[62][63][64] Additionally the frequency spectrum in most NMR experiments is substantially broadened inhomogeneously owing to a distribution in texture of the order parameter whose orientation relative to the magnetic field can generate a wide range of frequency shifts, Á!, which can be expressed 38) for pure 3 He as…”

Section: Identification Of the Superfluid State And Phase Diagrammentioning

confidence: 99%

“…It was suggested by Vicente et al 10) that the origin of this phase might be associated with anisotropic scattering. Subsequently, some theoretical work 11) and a number of experiments [12][13][14][15][16][17] have investigated 3 He in aerogels having global anisotropy, suggesting new order parameter structures and perhaps new kinds of superfluid phases. These questions and others have been the subject of intense activity.…”

Section: Introductionmentioning

confidence: 99%

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Impurity Effects of Aerogel in Superfluid³He

et al. 2008

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The discovery of superfluid 3 He in high porosity silica aerogels, and subsequent experimental and theoretical work, have led to a better general understanding of quasiparticle scattering from impurities in unconventional pairing systems. It is immensely helpful for understanding impurity effects in the case of superfluid 3 He that the structure of its order parameter is well-established. An overview of impurity effects is presented with emphasis on those experiments which have a quantitative interpretation in terms of theoretical models for homogeneous and inhomogeneous scattering. The latter can account successfully for most experimental results.

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Section: Nmr and Magnetizationmentioning

confidence: 99%

Section: Identification Of the Superfluid State And Phase Diagrammentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Impurity Effects of Aerogel in Superfluid³He

et al. 2008

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“…However, to date the interpretation of pulsed NMR experiments in aerogel has been complicated by distributions in the frequency shifts owing to spatially non-uniform directions of the angular momentum, called orbital textures, that can be attributed to structural inhomogeneity in aerogel samples on length scales larger than the superfluid coherence length, ξ 0 [5,[15][16][17][18].…”

Section: Superfluidmentioning

confidence: 99%

Identification of Superfluid Phases ofHe3in Uniformly Isotropic 98.2% Aerogel

Pollanen

Collett

et al. 2011

Phys. Rev. Lett.

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Superfluid3 He confined to high porosity silica aerogel is the paradigm system for understanding impurity effects in unconventional superconductors. However, a crucial first step has been elusive; exact identification of the microscopic states of the superfluid in the presence of quenched disorder. Using a new class of highly uniform aerogel materials, we report pulsed nuclear magnetic resonance experiments that demonstrate definitively that the two observed superfluid states in aerogel are impure versions of the isotropic and axial p-wave states. The theoretically predicted destruction of long-range orbital order (Larkin-Imry Ma effect) in the impure axial state is not observed.PACS numbers: 67.30. Hm, 67.30.Er, 67.30.Hj, 74.20.Rp The discovery of effects of quenched disorder on superfluid 3 He using high porosity silica aerogel [1, 2] has created an opportunity for systematic study of the role of impurities on unconventional pairing. Although the two observed superfluid phases in aerogel have characteristics similar to those of pure 3 He (where the A-phase is the axial state and the B-phase is the isotropic state), the identification of the states is lacking. Theory indicates that the presence of elastic quasiparticle scattering reduces strong coupling [3], which is known to be responsible for the axial state in pure 3 He. This should favor the isotropic state in aerogel, consistent with susceptibility and acoustic experiments [4][5][6]. However, a metastable phase is observed at high pressure on cooling, stabilized by magnetic field [6], and its identity is more in question. In this regard we note that without strong coupling, the planar and axial states are degenerate [7]. There are predictions that local or global anisotropy in the scattering rates favor various possible anisotropic states, e.g. axial [3], polar [8], or possibly a family of robust states [9]. Furthermore, random local disorder is predicted to lead to an orbitally disordered superfluid glass [10,11] or Larkin-Imry-Ma (LIM) state [12,13]. To resolve this problem, we have grown a new type of highly homogeneous aerogel and developed methods for its characterization [14]. In this Letter we present results on 3 He in a 98.2% porosity uniformly-isotropic aerogel sample in which we precisely determine the order parameter structure and identify the microscopic states of the superfluid phases to be the impurity suppressed axial and isotropic states. Additionally, we find no evidence for the existence of the predicted LIM superfluid glass.Pulsed NMR is a powerful technique for identifying the superfluid states of 3 He, where the frequency shifts of the spectrum are directly related to the amplitude of the order parameter, ∆, and the dependence of the shift on tip angle is a fingerprint of the microscopic state [7]. However, to date the interpretation of pulsed NMR experiments in aerogel has been complicated by distributions in the frequency shifts owing to spatially non-uniform directions of the angular momentum, called orbital textures, that can b...

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“…It was suggested that the shape of potential can be inverted and thus the coherent precession can be stabilized if the orbital momentum of Cooper pairs in 3 He-A is oriented along the applied magnetic field [5]. Recently such orientation has been reached for 3 He-A immersed in the axially squeezed aerogel [6], and the first experiments with the coherently precessing state (CPS) of magnetization have been reported [7]. Here we discuss the phenomenon of the coherent precession of magnetization in superfluid 3 He-A in terms of the Bose-Einstein condensation (BEC) of magnons, and consider the difference between magnon BEC states in 3 He-A (CPS) and in 3 He-B (HPD).…”

mentioning

confidence: 99%

Magnon BEC in superfluid 3He-A

Bunkov

Volovik²

2009

Jetp Lett.

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The new mode of magnetization precession in superfluid 3 He-A in a squeezed aerogel has been recently reported. We consider this mode in terms of the Bose-Einstein condensation (BEC) of magnons. The difference between magnon BEC states in 3 He-A and in 3 He-B is discussed. PACS:The discovery [1] and detailed investigations of the phase-coherent precession of magnetization in superfluid 3 He-B generated a search for similar phenomena in other systems. Superfluid 3 He-A could be a proper system. However, it was found that under typical conditions the coherent precession in 3 He-A is unstable [2] because of the convex shape of spin-orbit energy potential as function of magnetization [3,4]. It was suggested that the shape of potential can be inverted and thus the coherent precession can be stabilized if the orbital momentum of Cooper pairs in 3 He-A is oriented along the applied magnetic field [5]. Recently such orientation has been reached for 3 He-A immersed in the axially squeezed aerogel [6], and the first experiments with the coherently precessing state (CPS) of magnetization have been reported [7]. Here we discuss the phenomenon of the coherent precession of magnetization in superfluid 3 He-A in terms of the Bose-Einstein condensation (BEC) of magnons, and consider the difference between magnon BEC states in 3 He-A (CPS) and in 3 He-B (HPD). BEC is one of the most remarkable quantum phenomena. It corresponds to formation of collective quantum state, in which the macroscopic number of particles is governed by a single wave function. The formation of Bose-Einstein condensate was predicted by Einstein in 1925, for review see e.g. [8]. The almost perfect BEC state was observed in ultra could atomic gases. In Bose liquids, the BEC is strongly modified by interactions, but still remains the key mechanism for formation of coherent quantum state, which experiences the phenomenon of superfluidity: nondissipative superfluid current. In liquid 4 He the depletion of the condensate is very large: in the limit of zero temperature only about 10% of particles occupy the state with zero momentum. Nevertheless the whole liquid (100% of atoms) forms the 1) yuriy.bunkov@grenoble.cnrs.fr; volovik@boojum.hut.fi coherent quantum state at T = 0, so that the superfluid density equals the total density, ρ s (T = 0) = ρ. The latter is valid for any monoatomic superfluid system with translational invariance, including superfluid 3 He with the non BEC mechanism of coherent quantum state. If translational invariance is violated by impurities, crystal fields or other inhomogeneity, the superfluid component is suppressed:Superfluidity is a very general quantum property of matter at low temperatures, with variety of possible nondissipative superfluid currents, such as supercurrent of electric charge in superconductors; hypercharge supercurrent in the vacuum of Standard Model; supercurrent of color charge in a dense quark matter; etc. The origin of superfluidity is the spontaneous violation of the U (1) symmetry related to the conservation of ...

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Orientation effect on superfluid 3He in anisotropic aerogel

Cited by 65 publications

References 16 publications

Impurity Effects of Aerogel in Superfluid³He

Impurity Effects of Aerogel in Superfluid³He

Identification of Superfluid Phases ofHe3in Uniformly Isotropic 98.2% Aerogel

Magnon BEC in superfluid 3He-A

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Orientation effect on superfluid 3He in anisotropic aerogel

Cited by 65 publications

References 16 publications

Impurity Effects of Aerogel in Superfluid3He

Impurity Effects of Aerogel in Superfluid3He

Identification of Superfluid Phases ofHe3in Uniformly Isotropic 98.2% Aerogel

Magnon BEC in superfluid 3He-A

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Impurity Effects of Aerogel in Superfluid³He

Impurity Effects of Aerogel in Superfluid³He