Birefringence of hexagonal helium-4 at various densities

Vos, Jaap Jan; Kingma, R.; Gaag, F.J. van der; Blaisse, B.S.

doi:10.1016/0375-9601(67)90243-5

Cited by 21 publications

(10 citation statements)

References 2 publications

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“…8(a) together with previous results. 6,10,12,[14][15][16][17][18]52 Note that we use x-ray data only at 13 GPa. Nevertheless, the EOS determined here is quite close to recent x-ray diffraction results 36 over a wide pressure range.…”

Section: Equation Of Statementioning

confidence: 99%

“…Many experimental and theoretical investigations have been carried out to determine the crystal structure, phase diagram, equation of state, thermodynamic properties, and elasticity at high pressure. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Extensive investigations have also been done in the lowertemperature range because of its importance as a prototypical quantum system.…”

Section: Introductionmentioning

confidence: 99%

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Elasticity of dense helium

2004

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Brillouin scattering measurements have been conducted on crystals of 4 He at high pressure using diamond anvil cells. Complete sets of elastic moduli, aggregate sound velocities, adiabatic and isothermal equations of state, and other thermodynamic properties were obtained up to 32 GPa at room temperature. Although He adopts a hexagonal close-packed structure over the measured P-T range, its elasticity is close to that of a cubic material. The Cauchy condition is violated to an increasing degree with pressure and indicates an increasing role of noncentral forces such as many-body exchange interactions. The results provide detailed constraints on the density dependence of interatomic interactions and the associated lattice dynamics of this quantum solid.

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Section: Equation Of Statementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Elasticity of dense helium

2004

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“…Theoretically obtained dependences of the parameter d on the specific volume for solid 4 He are shown in Fig. 1.…”

Section: Solid Heliummentioning

confidence: 99%

“…Let us now turn to the equation of state P(V) for 4 He. The deviation from the ideal structure very slightly affects the behavior of P(V) so that for its calculation it is enough to retain only first term in Eq.…”

Section: Solid Heliummentioning

confidence: 99%

“…Experimentally, no conclusive data exist about the value of the parameter d at different pressures and temperatures. Vos et al [4] using an optical method based on the presence of birefrigence in the hcp phase found that the deviation of c/a from the ideal value is about -0.001 at the lowest density (20.6 cm 3 /mol) and decreases in magnitude at higher densities (-6×10 -4 at 1 kbar (20.6 cm 3 /mol)). Neutron diffraction gave the value c/a = 1.63 ± 0.03 for a molar volume of 18.51 cm 3 /mol [5], but a recalculation of Henshaw's data by Donohue [6] resulted in the value c/a = 1.612 ± 0.004.…”

Section: Introductionmentioning

confidence: 99%

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Lattice distortion of quantum cryocrystals under pressure

Tretyak

Antsygina

Freǐman

2006

Low Temperature Physics

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The hcp lattice distortion parameter @, the deviation of c/a ratio from the ideal hcp value 8 3 / , have been calculated for solid He under pressure taking into account two-and three-body interatomic forces. The resulting lattice distortion parameter is small and negative, that is the lattice is slightly flattened compared with the ideal hcp lattice. It monotonically increases in absolute value with pressure and reaches 10 -3 for molar volume of~2.5 cm 3 /mol. Such small distrotions are most likely outside of possibilities of x-ray or neutron experiments but can be detected by optical methods based on measurements of the birefringence. The data on @ can be used as a probe of the many-body forces.

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