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Search for Dislocation Free Helium 4 Crystals.

Souris F, Fefferman AD, Haziot A, Garroum N, Beamish JR, Balibar S - J Low Temp Phys (2014)

Bottom Line: In 1996-1998, Ruutu et al. published crystal growth studies showing that, in their helium 4 crystals, the density of screw dislocations along the c-axis was less than 100 per cm[Formula: see text], sometimes zero.We have grown helium 4 crystals using similar growth speeds and temperatures, and extracted their dislocation density from their mechanical properties.We found dislocation densities that are in the range of 10[Formula: see text]-10[Formula: see text] per cm[Formula: see text], that is several orders of magnitude larger than Ruutu et al.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Physique Statistique de l'École Normale Supérieure associé au CNRS et aux Universités P.M. Curie et D. Diderot, 24 rue Lhomond, 75231 Paris Cedex 05, France.

ABSTRACT

The giant plasticity of [Formula: see text]He crystals has been explained as a consequence of the large mobility of their dislocations. Thus, the mechanical properties of dislocation free crystals should be quite different from those of usual ones. In 1996-1998, Ruutu et al. published crystal growth studies showing that, in their helium 4 crystals, the density of screw dislocations along the c-axis was less than 100 per cm[Formula: see text], sometimes zero. We have grown helium 4 crystals using similar growth speeds and temperatures, and extracted their dislocation density from their mechanical properties. We found dislocation densities that are in the range of 10[Formula: see text]-10[Formula: see text] per cm[Formula: see text], that is several orders of magnitude larger than Ruutu et al. Our tentative interpretation of this apparent contradiction is that the two types of measurements are somewhat indirect and concern different types of dislocations. As for the dislocation nucleation mechanism, it remains to be understood.

No MeSH data available.


Related in: MedlinePlus

The resonance frequency of P3 as a function of  computed with a numerical model of the cavity. A picture of the crystal is shown on the right inset with its sixfold symmetry axis along the  axis. The left inset shows an effective pressure field of the vibration mode studied for P3, defined as the trace of the stress tensor. The location of the pressure anti-nodes makes this vibration mode strongly coupled to our detection system (Color figure online)
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Fig3: The resonance frequency of P3 as a function of computed with a numerical model of the cavity. A picture of the crystal is shown on the right inset with its sixfold symmetry axis along the axis. The left inset shows an effective pressure field of the vibration mode studied for P3, defined as the trace of the stress tensor. The location of the pressure anti-nodes makes this vibration mode strongly coupled to our detection system (Color figure online)

Mentions: For every oriented crystal, a numerical model of the resonant cavity was produced with COMSOL software and used to predict the dependence of the resonance frequency on the value of . An example for the crystal P3 is shown on Fig. 3, for which the sixfold axis of symmetry is almost along to the axis. For this crystal, when is varied from zero to its intrinsic value , the resonance frequency varies almost linearly from to  kHz. This calibration curve is subsequently used to convert the measured resonance frequencies into values. The accuracy of the numerical model was tested with several crystals in a fully pinned regime, where the value of is equal to the intrinsic value measured by Greywall [16] at  K and  MHz. Among different crystal orientations, the disagreement between the predicted value and the measured value of the resonance frequency never exceeded  %. For example, for the measurement presented in Fig. 2, the measured frequency is  kHz, while the predicted value is  kHz. These  % are likely due to a slight error in the cell size measurement and, in any case, compatible with Greywall’s error bars. This agreement confirms the validity of our numerical calculation.Fig. 3


Search for Dislocation Free Helium 4 Crystals.

Souris F, Fefferman AD, Haziot A, Garroum N, Beamish JR, Balibar S - J Low Temp Phys (2014)

The resonance frequency of P3 as a function of  computed with a numerical model of the cavity. A picture of the crystal is shown on the right inset with its sixfold symmetry axis along the  axis. The left inset shows an effective pressure field of the vibration mode studied for P3, defined as the trace of the stress tensor. The location of the pressure anti-nodes makes this vibration mode strongly coupled to our detection system (Color figure online)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4459123&req=5

Fig3: The resonance frequency of P3 as a function of computed with a numerical model of the cavity. A picture of the crystal is shown on the right inset with its sixfold symmetry axis along the axis. The left inset shows an effective pressure field of the vibration mode studied for P3, defined as the trace of the stress tensor. The location of the pressure anti-nodes makes this vibration mode strongly coupled to our detection system (Color figure online)
Mentions: For every oriented crystal, a numerical model of the resonant cavity was produced with COMSOL software and used to predict the dependence of the resonance frequency on the value of . An example for the crystal P3 is shown on Fig. 3, for which the sixfold axis of symmetry is almost along to the axis. For this crystal, when is varied from zero to its intrinsic value , the resonance frequency varies almost linearly from to  kHz. This calibration curve is subsequently used to convert the measured resonance frequencies into values. The accuracy of the numerical model was tested with several crystals in a fully pinned regime, where the value of is equal to the intrinsic value measured by Greywall [16] at  K and  MHz. Among different crystal orientations, the disagreement between the predicted value and the measured value of the resonance frequency never exceeded  %. For example, for the measurement presented in Fig. 2, the measured frequency is  kHz, while the predicted value is  kHz. These  % are likely due to a slight error in the cell size measurement and, in any case, compatible with Greywall’s error bars. This agreement confirms the validity of our numerical calculation.Fig. 3

Bottom Line: In 1996-1998, Ruutu et al. published crystal growth studies showing that, in their helium 4 crystals, the density of screw dislocations along the c-axis was less than 100 per cm[Formula: see text], sometimes zero.We have grown helium 4 crystals using similar growth speeds and temperatures, and extracted their dislocation density from their mechanical properties.We found dislocation densities that are in the range of 10[Formula: see text]-10[Formula: see text] per cm[Formula: see text], that is several orders of magnitude larger than Ruutu et al.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Physique Statistique de l'École Normale Supérieure associé au CNRS et aux Universités P.M. Curie et D. Diderot, 24 rue Lhomond, 75231 Paris Cedex 05, France.

ABSTRACT

The giant plasticity of [Formula: see text]He crystals has been explained as a consequence of the large mobility of their dislocations. Thus, the mechanical properties of dislocation free crystals should be quite different from those of usual ones. In 1996-1998, Ruutu et al. published crystal growth studies showing that, in their helium 4 crystals, the density of screw dislocations along the c-axis was less than 100 per cm[Formula: see text], sometimes zero. We have grown helium 4 crystals using similar growth speeds and temperatures, and extracted their dislocation density from their mechanical properties. We found dislocation densities that are in the range of 10[Formula: see text]-10[Formula: see text] per cm[Formula: see text], that is several orders of magnitude larger than Ruutu et al. Our tentative interpretation of this apparent contradiction is that the two types of measurements are somewhat indirect and concern different types of dislocations. As for the dislocation nucleation mechanism, it remains to be understood.

No MeSH data available.


Related in: MedlinePlus