Observation of a new superfluid phase for 3He embedded in nematically ordered aerogel

Zhelev, Nikolay; Reichl, Matthew D.; Abhilash, T. S.; Smith, Eric N.; Nguyen, Kayla X.; Mueller, Erich J.; Parpia, J. M.

doi:10.1038/ncomms12975

Cited by 37 publications

(35 citation statements)

References 24 publications

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“…Recently the interest to study superfluids in aerogels also arose due to the observation of polar superfluid phases in nematically ordered aerogels. 2,3 The ballistic mean-free path (mfp) in an aerogel l aero is an important parameter for theoretical models of 3 He superfluidity and can be determined by diffusion experiments, for instance, via magnetic resonance with pulse gradients. At very low temperatures (o10 mK) the density of quasiparticles in liquid is so small that its mfp is defined by quasiparticle-aerogel collisions [4][5][6] and coincides with the ballistic mean-free path in the aerogel.…”

Section: Introductionmentioning

confidence: 99%

Helium-3 gas self-diffusion in a nematically ordered aerogel at low temperatures: enhanced role of adsorption

Kuzmin

Safiullin

Stanislavovas

et al. 2017

Phys. Chem. Chem. Phys.

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We performed 3 He gas diffusion measurements for the first time in a highly porous ordered Al 2 O 3 aerogel sample at a temperature of 4.2 K using a nuclear magnetic resonance field gradient technique.A strong influence of 3 He adsorption in the aerogel on self-diffusion is observed. The classical consideration of adsorptive gas diffusion in mesopores leads to anomalously high tortuosity factors. The application of a more sophisticated model than the simple combination of empirical two-phase diffusion and the Knudsen gas diffusion models is required to explain our results. Anisotropic properties of the aerogel are not reflected in the observed gas diffusion even at low gas densities where the anisotropic Knudsen regime of diffusion is expected. The observed gas densification indicates the influence of the aerogel attractive potential on the molecular dynamics, which probably explains the reduced diffusion process. Perhaps this behavior is common for any adsorptive gases in nanopores.

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Section: Introductionmentioning

confidence: 99%

Helium-3 gas self-diffusion in a nematically ordered aerogel at low temperatures: enhanced role of adsorption

Kuzmin

Safiullin

Stanislavovas

et al. 2017

Phys. Chem. Chem. Phys.

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“…polar, polar distorted A (denoted as DA), and polar distorted B (denoted as DB) phases [24][25][26][27]. These phases were recently observed in experiments with 3 He in N-aerogels [28][29][30][31]. We note that aerogel strands in Refs.…”

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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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“…However, the results and the analysis presented in this paper can be extended to other phases and systems that host surface Andreev states, e.g. p-wave superconductors [48][49][50][51][52] .…”

Section: Discussionmentioning

confidence: 98%

Spontaneous symmetry breaking at surfaces of d -wave superconductors: Influence of geometry and surface ruggedness

et al. 2019

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Surfaces of d-wave superconductors may host a substantial density of zero-energy Andreev states. The zero-energy flat band appears due to a topological constraint, but comes with a cost in free energy. We have recently found that an adjustment of the surface states can drive a phase transition into a phase with finite superflow that breaks time-reversal symmetry and translational symmetry along the surface. The associated Doppler shifts of Andreev states to finite energies lower the free energy. Direct experimental verification of such a phase is still technically difficult and controversial, however. To aid further experimental efforts, we use the quasiclassical theory of superconductivity to investigate how the realization and the observability of such a phase are influenced by sample geometry and surface ruggedness. Phase diagrams are produced for relevant geometric parameters. In particular, critical sizes and shapes are identified, providing quantitative guidelines for sample fabrication in the experimental hunt for symmetry-breaking phases. arXiv:1902.07530v1 [cond-mat.supr-con]

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Observation of a new superfluid phase for 3He embedded in nematically ordered aerogel

Cited by 37 publications

References 24 publications

Helium-3 gas self-diffusion in a nematically ordered aerogel at low temperatures: enhanced role of adsorption

Helium-3 gas self-diffusion in a nematically ordered aerogel at low temperatures: enhanced role of adsorption

Effect of Magnetic Boundary Conditions on SuperfluidHe3in Nematic Aerogel

Spontaneous symmetry breaking at surfaces of d -wave superconductors: Influence of geometry and surface ruggedness

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