Vacancy induced atomic motion in3He-4He mixture crystals on the melting curve studied by NMR imaging

Schuster, Israel; Polturak, E.; Swirsky, Y.; Schmidt, Ehud J.; Lipson, S. G.

doi:10.1007/bf00755975

Cited by 12 publications

(2 citation statements)

References 31 publications

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“…As in the bcc phase, evidence for the existence of a "local mode" comes from NMR measurements 6,22 of the linewidth (1/T 2 ) with energy ≃ 14K. We propose therefore that the NMR experiments measure the energy of the bare local mode.…”

Section: Local Modes In Hcp 4 Hementioning

confidence: 94%

Local modes, phonons, and mass transport in solid4He

Gov

Polturak²

1999

Phys. Rev. B

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We propose a model to treat the local motion of atoms in solid 4 He as a local mode. In this model, the solid is assumed to be described by the self-consistent harmonic approximation, combined with an array of local modes. We show that in the bcc phase the atomic local motion is highly directional and correlated, while in the hcp phase there is no such correlation. The correlated motion in the bcc phase leads to a strong hybridization of the local modes with the T 1 (110) phonon branch, which becomes much softer than that obtained through a self-consistent harmonic calculation, in agreement with experiment. In addition, we predict a high-energy excitation branch that is important for self-diffusion. Both the hybridization and the presence of a high-energy branch are a consequence of the correlation, and appear only in the bcc phase. We suggest that the local modes can play the role in mass transport usually attributed to point defects ͑vacancies͒. Our approach offers a more overall consistent picture than obtained using vacancies as the predominant point defect. In particular, we show that our approach resolves the long-standing controversy regarding the contribution of point defects to the specific heat of solid 4 He.

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Section: Local Modes In Hcp 4 Hementioning

confidence: 94%

Local modes, phonons, and mass transport in solid4He

Gov

Polturak²

1999

Phys. Rev. B

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“…Applying the Fourier analysis to each spin echo within the standard spin-echo sequences yields a spatial map of the dynamic properties as reflected in the relaxation times T 1 and T 2 , and of the diffusion coefficient D. Since ρ 3 in the solid is not very different from that in the liquid, the real contrast between the two phases is provided by the difference in their T 1 and T 2 . Additional details regarding the NMR imaging experiment will be published elsewhere [6], [7].…”

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confidence: 99%

Observation of rapid atomic motion in solid ³ He- ⁴ He mixtures using NMR

et al. 1996

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We compared liquid and solid 3 He-4 He mixtures at coexistence using NMR imaging of the density of 3 He and of the T2 relaxation time in the two phases. We find that above 1 K, 3 He atoms in a bcc solid are more mobile than in the superfluid liquid. This rapid motion, induced by vacancies, takes place on a microscopic scale and can be explained in terms of 3 He-vacancy attraction of quantum origin. We relate our observations to similar effects observed in Sn-Pb alloys.

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