Structure and properties of “nematically ordered” aerogels

Асадчиков, В. Е.; Askhadullin, R.Sh.; Волков, В. В.; Дмитриев, В. В.; Kitaeva, N. K.; Мартынов, П. Н.; Осипов, А. И.; Senin, A. A.; Солдатов, А. А.; Chekrygina, D.; Yudin, A. N.

doi:10.1134/s0021364015080020

Cited by 59 publications

(73 citation statements)

References 12 publications

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“…We can conclude that the experimental values qualitatively agree with the theoretical model. The quantitative difference may be due to experimental errors in determination of D, errors in nafen parameters, and variations of strands diameters (by ±20% as follows from [10]). …”

Section: Discussionmentioning

confidence: 99%

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Anisotropic spin diffusion in liquid 3He confined in nafen

et al. 2015

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We report results of spin diffusion measurements in normal phase of liquid 3 He confined in nafen. Nafen is a new type of aerogel and it consists of Al2O3 strands which are nearly parallel to one another at macroscopic distances. We examine two samples of nafen with different porosities using spin echo techniques. Spin diffusion of 3 He along and across the strands was measured. The aerogel alignment is clearly evident from observed spin diffusion anisotropy. A theory describing this effect is developed and compared with the experiment.

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Section: Discussionmentioning

confidence: 99%

“…Their structure was investigated in [10]. The samples consist of strands with diameter of ≈ 8 nm and ≈ 9 nm correspondingly.…”

Section: Details Of Experimentsmentioning

confidence: 99%

Anisotropic spin diffusion in liquid 3He confined in nafen

et al. 2015

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“…The situation may be different for essentially anisotropic scattering but it has not been investigated earlier. To obtain the anisotropic scattering a "nematic" aerogel (N-aerogel) [21] can be used. Its strands are nearly parallel to one another, and at ultralow temperatures an effective mean free path of 3 He quasiparticles along the strands directionζ is longer than in the transverse direction [22,23].…”

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confidence: 99%

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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“…It consists of Al 2 O 3 strands with diameters of ∼ 9 nm and has a porosity of 93.9%. More information about the sample can be found in [5].…”

Section: Details Of Experimentsmentioning

confidence: 99%

“…Diameters of the strands (∼ 10 nm) are less than the superfluid coherence length of 3 He, so in the case of liquid 3 He confined in N-aerogel these strands play a role of anisotropic impurities, and theory predicts that superfluid phases which do not exist in bulk 3 He may become favorable, namely the polar-distorted A phase, the polar-distorted B phase and the pure polar phase [1,2,3,4]. There are two types of N-aerogel: "Obninsk aerogel" and nafen [5]. Polar-distorted A and B phases have been observed in 3 He confined in Obninsk aerogel [6,7,8], while the pure polar phase is realized in 3 He in nafen [9].…”

Section: Introductionmentioning

confidence: 99%

Interaction of two magnetic resonance modes in the polar phase of superfluid 3He

2016

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We report results of low frequency nuclear magnetic resonance (NMR) experiments in the superfluid polar phase of 3 He which is stabilized by a new type of "nematic" aerogel -nafen. We have found that an interaction between transverse and longitudinal NMR modes may essentially influence the spin dynamics. Theoretical formulas for NMR resonant frequencies are derived and applied for interpretation of the experimental results.

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Structure and properties of “nematically ordered” aerogels

Cited by 59 publications

References 12 publications

Anisotropic spin diffusion in liquid 3He confined in nafen

Anisotropic spin diffusion in liquid 3He confined in nafen

Effect of Magnetic Boundary Conditions on SuperfluidHe3in Nematic Aerogel

Interaction of two magnetic resonance modes in the polar phase of superfluid 3He

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