Observation of macroscopic structural fluctuations in bcc solid<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mi>He</mml:mi><mml:none /><mml:none /><mml:mprescripts /><mml:none /><mml:mn>4</mml:mn></mml:mmultiscripts></mml:mrow></mml:math>

Pelleg, O.; Shay, Meni; Lipson, S. G.; Polturak, E.; Bossy, J.; Marmeggi, J.C.; Horibe, K.; Farhi, Emmanuel; Stunault, A.

doi:10.1103/physrevb.73.024301

Cited by 14 publications

(16 citation statements)

References 19 publications

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“…As a result, internal stress is generated, large enough to cause the crystal to disorder and transform into a polycrystal. This behavior is consistent with what we observed in neutron scattering experiments [1]. It is important to point out that the crystal can be disordered only after the cell is entirely filled with solid.…”

Section: Solidsupporting

confidence: 91%

“…During these experiments we grew large (7-10 cm 3 ) single crystals, which sometimes transformed into polycrystals due to some thermal or mechanical stress. In those cases, we noticed that individual crystallites which are part of a polycrystalline solid can spontaneously change their spatial orientation while embedded in the surrounding solid [1]. These orientation changes seemed to be driven by ambient noise, either vibrational or thermal.…”

Section: Solidmentioning

confidence: 99%

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Characterization of the Surface of Moving Solid $$^4$$ 4 He

et al. 2015

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Crystal grains of solid4 He can move in relation to each other even when embedded inside the solid [1,2]. In this work, we characterize a macroscopic motion of solid hcp 4 He composed of such grains. Motion is induced by applying an external torque to the solid contained inside an annular channel mounted on a torsional oscillator. In order to characterize the surface of the moving solid, we developed an in-situ flow detection method using a sensitive "microphone" embedded in the wall of the channel. Motion is detected by counting the vibrations induced by rows of He atoms moving past the microphone. Such vibrations were detected only at T=0.5K, our lowest temperature. At this temperature, the measured dissipation associated with the solid He is zero within our accuracy. Our results indicate that the orientation of the surface of the moving solid is the (0001) basal plane of the hcp structure. At T=0.5 K, we found that for speeds < 7 µm/sec, the solid flows without detectable friction.

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Section: Solidsupporting

confidence: 91%

Section: Solidmentioning

confidence: 99%

Characterization of the Surface of Moving Solid $$^4$$ 4 He

et al. 2015

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“…Similar behavior was observed in neutron scattering experiments 22,23 , with the c axis of hcp crystals again being close to horizontal. Regarding bcc crystals, we found that these typically grow with the [111] direction close to vertical 22,24,23 . Therefore, experiments on different crystals in the same cell are usually quite reproducible, as most of these crystals would grow with the same crystallographic direction with respect to the cell.…”

Section: Experimental Systemmentioning

confidence: 97%

BCC vs. HCP—The Effect of Crystal Symmetry on the High Temperature Mobility of Solid 4He

Eyal

Polturak²

2012

J Low Temp Phys

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We report results of torsional oscillator (TO) experiments on solid 4 He at temperatures above 1K. We have previously found that single crystals, once disordered, show some mobility (decoupled mass) even at these rather high temperatures. The decoupled mass fraction with single crystals is typically 20-30%. In the present work we performed similar measurements on polycrystalline solid samples. The decoupled mass with polycrystals is much smaller, ∼ 1%, similar to what is observed by other groups. In particular, we compared the properties of samples grown with the TO's rotation axis at different orientations with respect to gravity. We found that the decoupled mass fraction of bcc samples is independent of the angle between the rotation axis and gravity. In contrast, hcp samples showed a significant difference in the fraction of decoupled mass as the angle between the rotation axis and gravity was varied between zero and 85 degrees. Dislocation dynamics in the solid offers one possible explanation of this anisotropy.

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“…For that, we first needed to grow single crystals of helium inside the experimental cell. Our knowledge of single crystal growth comes mainly from neutron scattering experiments [20,17]. During these experiments elastic scattering was used to characterize the quality and orientation of the crystals grown.…”

Section: Crystal Growthmentioning

confidence: 99%

On the Mobile Behavior of Solid 4He at High Temperatures

Eyal¹,

Polturak²

2011

J Low Temp Phys

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We report studies of solid helium contained inside a torsional oscillator, at temperatures between 1.07K and 1.87K. We grew single crystals inside the oscillator using commercially pure 4 He and 3 He-4 He mixtures containing 100 ppm 3 He. Crystals were grown at constant temperature and pressure on the melting curve. At the end of the growth, the crystals were disordered, following which they partially decoupled from the oscillator. The fraction of the decoupled He mass was temperature and velocity dependent. Around 1K, the decoupled mass fraction for crystals grown from the mixture reached a limiting value of around 35%. In the case of crystals grown using commercially pure 4 He at temperatures below 1.3K, this fraction was much smaller. This difference could possibly be associated with the roughening transition at the solid-liquid interface.

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Observation of macroscopic structural fluctuations in bcc solidHe4

Cited by 14 publications

References 19 publications

Characterization of the Surface of Moving Solid $$^4$$ 4 He

Characterization of the Surface of Moving Solid $$^4$$ 4 He

BCC vs. HCP—The Effect of Crystal Symmetry on the High Temperature Mobility of Solid 4He

On the Mobile Behavior of Solid 4He at High Temperatures

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