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ABSTRACT: The energies of excitations in the region of the minimum in the dispersion curve for superfluid liquid 4He have been determined at SVP and T=0.75K using neutron inelastic scattering. The value of Delta /k is 8.618+or-0.009K. Comparison with recent Raman-scattering measurements gives a value of the roton-roton binding energy of 0.027+or-0.04K at Q=0.
Journal of Physics C Solid State Physics 02/2001; 10(3):L45.
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ABSTRACT: The neutron scattering from liquid helium 3 at 0.63K, and at its saturated vapour pressure, has been measured using the IN5 time-of-flight spectrometer situated on the cold source of the high flux reactor. The measurements, which cover momentum transfers between 1.0 and 2.5 AA-1 and energy transfers between 0.5 and 4.0 meV, show that the scattering has a broad spectrum without the well defined excitations found in superfluid liquid 4He. The maxima of the spectra are at energies of less than 1.0 meV for wavevectors below 1.8 AA-1 but then increase in energy to 3.0 meV at the largest wavevector transfers. The results are compared with calculations based on variants of the random phase approximation. The comparison suggests that it is necessary to include in the calculation the self-energy of the single-particle states and the effect of the multi-particle excitations.
Journal of Physics C Solid State Physics 02/2001; 9(9):1643.
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ABSTRACT: Zero-sound excitations in liquid 3He at 0.02K and at the pressure of the saturated vapour have been studied using neutron inelastic scattering techniques. The results for the frequencies of the zero-sound excitations are in agreement with the measurements of Skold and co-workers. The results also show a non-zero linewidth for the excitations with wave-vector transfers 0.45 AA-1<Q<0.8 AA-1, which suggests that modification to the current theories is required.
Journal of Physics C Solid State Physics 11/2000; 13(12):L295.
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ABSTRACT: The inelastic neutron scattering from liquid3He at 0.7 K has been measured at the saturated vapour pressure, 10 bars, and 20 bars pressure, using the IN5 time of flight spectrometer at the Institut Laue-Langevin. Results were obtained for wavevector transfers,Q, in the region, 1.1Q–1, and for energy transfers,, up to 27 K. There was no indication of a well defined zero sound mode even at an applied pressure of 20 bars. At low wavevector transfers, increasing the pressure increases the intensity at low energy transfers (Q1.9 –1, the position of the roton minimum in superfluid4He), the scattering is a broad distribution, whose peak frequency decreases by more than a factor of 2, on increasing the pressure from S.V.P. to 20 bars. This is a considerably larger change in energy than is expected from previous estimates of the pressure dependence of the effective mass of3He.
Zeitschrift für Physik B Condensed Matter 05/1978; 30(2):107-110.
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ABSTRACT: Neutron inelastic scattering techniques have been used to study the excitation spectrum of mixtures containing 6%, 12%, and 25% of3He in4He at 0.75 K. The 6% mixture has also been investigated at temperatures of 0.6, 1.0, and 1.5 K. The measurements have been made in the wave-vector transfer rangeQ=0.8–2.3 –1. The energy spectra observed contain two principal features, which are interpreted as scattering from (a) phonon-roton excitations arising from the4He, and (b) quasiparticle-quasihole excitations arising from the3He. In the dilute3He-4He mixture, our results indicate a3He particle-hole continuum which deviates from the quadratic form, proposed by Landau and Pomeranchuk, and which lies below the4He phonon-roton dispersion curve. However, we are unable to say whether or not the continuum exhibits a minimum as a function of energy, as has recently been proposed by several authors, because we were unable to resolve the scattering from the particle-hole continuum forQ1.7 –1. In this region ofQ space the energy spectra are dominated by the roton excitations. We have also determined the shifts in energy and increases in linewidth of the phonon-roton excitations relative to those of pure4He and compared these measurements to several theoretical predictions.
Journal of Low Temperature Physics 05/1977; 27(5):851-872. · 1.19 Impact Factor
