Inelastic-Neutron Scattering from bcc<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>

Osgood, E. B.; Minkiewicz, V. J.; Kitchens, T. A.; Shirane, G.

doi:10.1103/physreva.5.1537

Cited by 105 publications

(20 citation statements)

References 33 publications

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“…The measured phonon spectrum of bcc 4 He is very similar to that of metals. The measured spectrum [14,15] is in very good agreement with theoretical calculations [16] done at T 0, except for the same ͑j, j, 0͒ transverse phonon branch, which appears to be much softer. We therefore take the view that the mechanism of self-diffusion in bcc 4 He is the same as in bcc metals, and the decrease of E͑T ͒ near the transition results from the softening of this phonon.…”

Section: Inon Berent and Emil Polturaksupporting

confidence: 84%

Critical Behavior of the Shear Resistance of Solid4Henear a Structural Phase Transition

Berent

Polturak

1998

Phys. Rev. Lett.

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We describe experiments on plastic flow of solid 4 He near the first order bcc-hcp transition. We find that the resistance to shear of the solid diminishes strongly near the transition. We are able to distinguish between plastic flow due to vacancies and due to dislocations, and show that the critical behavior of the solid near the transition is controlled by vacancy diffusion. The enhancement of the diffusion is consistent with a coupling of the vacancies to a phonon which softens near the transition. Possible implications of our findings on the understanding of melting are discussed.[S0031-9007(98)06732-5] PACS numbers: 67.80.Mg, 62.20.Hg, 64.70.Dv In an experiment aimed at measuring the plastic flow properties of solid He, we found that the shear resistance of the solid decreases dramatically as the temperature nears that of a bcc-hcp phase transition [1]. Over a temperature interval of 0.1 K, the plastic flow rate increased by 1 1 2 orders of magnitude. In that experiment, the flow of solid took place by diffusion, yielding a value of the diffusion coefficient at the transition typical of a liquid. The loss of resistance to shear is the most prominent feature associated with melting. Theories of bulk melting proposed over the years rely on the sudden proliferation of crystalline defects in order to destabilize the lattice [2] so that the shear resistance vanishes. These include point defects (vacancies or interstitials) or line defects, namely, dislocations. However, this scenario was never confirmed experimentally, as the equilibrium density of defects in conventional solids is rather small, and it is impossible to approach the transition close enough to see critical behavior of the defects. The first order bcc-hcp structural phase transition in solid 4 He offers several advantages in this type of study. First, it is weakly first order (the entropy change per particle is 12 times less than that associated with melting [3]), and consequently the temperature interval where pretransition effects can be observed is wider. One can therefore resolve how the shear resistance changes as the phase transition is approached. Second, the estimated density of vacancies [4] in 4 He is significantly higher than what can be achieved in conventional solids even at the melting temperature. This condition of having a high defect density is another indispensable feature of the models of melting. Third, macroscopic single crystals of very high quality and purity can be grown. Furthermore, by investigating the plastic flow rate over a wide range of applied stresses, we can decide which type of defect, vacancies or dislocations, is responsible for the critical behavior near the transition (at low stress plastic flow results from vacancy diffusion, while at higher stress moving dislocations determine the rate). Thus, solid He is an excellent model system in which effects typical of the approach to the melting transition, such as loss of shear resistance and high defect density, can be conveniently studied. In this Letter we repo...

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Section: Inon Berent and Emil Polturaksupporting

confidence: 84%

Critical Behavior of the Shear Resistance of Solid4Henear a Structural Phase Transition

Berent

Polturak

1998

Phys. Rev. Lett.

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“…Our data for the three phonon branches is in excellent agreement with previous experiments [7,8]. The fact that the T 1 branch is lower by a factor of ∼ 2 compared with the SCP calculation was already evident from the previous experiments [7,8], and is confirmed in the present work. In addition, Fig.…”

supporting

confidence: 93%

“…The self consistent phonon (SCP) theory which emerged over the years, treats these short range correlations using Jastrow-type wavefunctions in the description of the ground state [1][2][3][4][5][6], in addition to the inclusion of anharmonic terms in the potential. Phonon dispersion curves calculated in the SCP theory are in good agreement with neutron scattering experiments on solid 4 He [7,8], except for the T 1 [110] branch of bcc 4 He, which experimentally has a much lower energy. In addition, the SCP theory was able to explain several observations unique to quantum solids, such as multiphonon scattering which dominates the scattering already at intermediate momentum transfer Q, and phonon interference which gives rise to oscillations of the effective Debye Waller factor.…”

supporting

confidence: 70%

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Observation of a New Excitation in bccH4eby Inelastic Neutron Scattering

Markovich

Polturak

Bossy³

et al. 2002

Phys. Rev. Lett.

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“…628 K and n s = 0 . 0287 A Ê -3 (Osgood et al 1971). The density response function is also known for liquid 4 He near freezing at T = 0 and n l = 0 .…”

Section: Numerical Estimates For 4 Hementioning

confidence: 96%