Orbital glass and spin glass states of 3He-A in aerogel

Дмитриев, В. В.; Krasnikhin, D. A.; Mulders, N.; Senin, A. A.; Volovik, G. E.; Yudin, A. N.

doi:10.1134/s0021364010110123

Cited by 62 publications

(65 citation statements)

References 23 publications

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“…However, experiments with silica aerogels do not show a clear evidence of the magnetic channel. In particular, the observed A-like and B-like phases correspond to A and B phases of bulk 3 He, regardless of presence or absence of 4 He [8][9][10][11][12][13][14]. Moreover, the superfluid transition temperature of 3 He in aerogel (T ca ) is independent on the coverage at high pressures [8,12] but slightly higher in presence of the coverage at lower pressures [15,16] probably due to the change of the scattering specularity.…”

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confidence: 86%

“…However, in DA and A phases a metastable spin glass (SG) state with random d also may exist that corresponds to a local minimum of energy. The SG state can be created in NMR experiments by cooling through T ca with high excitation that generates a random d-distribution [13]. On further cooling, this state is stabilized by the random n-field due to a dipole interac-…”

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confidence: 99%

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Effect of Magnetic Boundary Conditions on SuperfluidHe3in Nematic Aerogel

2018

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We report results of experiments with superfluid 3 He confined in aerogels with parallel strands which lead to anisotropic scattering of 3 He quasiparticles. We vary boundary conditions for the scattering by covering the strands by different numbers of atomic 4 He layers and observe that the superfluid phase diagram and the nature of superfluid phases strongly depend on the coverage. We assume that the main reason of these phenomena is a magnetic channel of the scattering which becomes important at low coverages. Our results show that the magnetic channel also may be important in other Fermi systems with the triplet pairing.Introduction.-In many Fermi systems, e.g. in liquid 3 He, in some cold atomic gases, and unconventional superconductors, a triplet Cooper pairing occurs that results in superfluid (superconducting) states. An ideal object to study an effect of impurities on such states is 3 He: it has a spherical Fermi surface, its superfluid phases (A, B and A 1 ) are well understood, and its superfluid coherence length can be varied by pressure in range of 20-80 nm [1]. Although superfluid 3 He is originally pure, a well defined system of impurities can be introduced by a high porosity aerogel. In such experiments silica aerogels are typically used. The main effect of the aerogel is to scatter 3 He quasiparticles. At temperatures T ∼ 1 mK, where 3 He is superfluid, the scattering occurs only on aerogel strands and boundary conditions may be varied by a small amount of 4 He which covers the strands by a few atomic layers. In pure 3 He the strands are covered by ∼ 2 atomic layers of paramagnetic solid 3 He [2] and the scattering is diffusive but in presence of more than ≈ 2.5 layers of 4 He it is nearly specular at low pressures and becomes purely diffusive above ≈ 25 bar [3][4][5][6][7]. The 4 He coverage also removes the solid 3 He, and spin is conserved during the scattering. In contrast, in pure 3 He spin is not conserved due to a fast exchange between atoms of liquid and solid 3 He that should result in an additional spin-exchange (magnetic) scattering channel. However, experiments with silica aerogels do not show a clear evidence of the magnetic channel. In particular, the observed A-like and B-like phases correspond to A and B phases of bulk 3 He, regardless of presence or absence of 4 He [8][9][10][11][12][13][14]. Moreover, the superfluid transition temperature of 3 He in aerogel (T ca ) is independent on the coverage at high pressures [8,12] but slightly higher in presence of the coverage at lower pressures [15,16] probably due to the change of the scattering specularity. In most of theoretical models of 3 He in aerogel the magnetic channel is neglected except only a few papers where it was shown that the magnetic scattering may affect A-A 1 transition in high magnetic fields [17][18][19] and a heat transport in the normal phase [20].Presumably, the magnetic scattering in 3 He in silica aerogels is masked due to their small global anisotropy.

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Effect of Magnetic Boundary Conditions on SuperfluidHe3in Nematic Aerogel

2018

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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].…”

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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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“…The magnetic field angle λ can be tuned in experiments continuously from the stable to the unstable region. Such transition has been discussed for 3 He-A 34,35 and observed in the disordered Larkin-Imry-Ma state of 3 He in aerogel 30 . Here we considered this transition and condensate instability in terms of the effective phonon metric.…”

Section: Superfluidmentioning

confidence: 99%

Effective Minkowski-to-Euclidean signature change of the magnon BEC pseudo-Goldstone mode in polar 3He

Nissinen

Volovik

2017

Jetp Lett.

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We discuss the effective metric experienced by the Nambu-Goldstone mode propagating in the broken symmetry spin-superfluid state of coherent precession of magnetization. This collective mode represents the phonon in the RF driven or pulsed out-of-equilibrium Bose-Einstein condensate (BEC) of optical magnons. We derive the effective BEC free energy and consider the phonon spectrum when the spin superfluid BEC is formed in the anisotropic polar phase of superfluid 3 He, experimentally observed in uniaxial aerogel 3 He-samples. The coherent precession of magnetization experiences an instability at a critical value of the tilting angle of external magnetic field with respect to the anisotropy axis. From the action of quadratic deviations around equilibrium, this instability is interpreted as a Minkowski-to-Euclidean signature change of the effective phonon metric. We also note the similarity between the magnon BEC in the unstable region and an effective vacuum scalar "ghost" condensate.

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Orbital glass and spin glass states of 3He-A in aerogel

Cited by 62 publications

References 23 publications

Effect of Magnetic Boundary Conditions on SuperfluidHe3in Nematic Aerogel

Effect of Magnetic Boundary Conditions on SuperfluidHe3in Nematic Aerogel

Identification of Superfluid Phases ofHe3in Uniformly Isotropic 98.2% Aerogel

Effective Minkowski-to-Euclidean signature change of the magnon BEC pseudo-Goldstone mode in polar 3He

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