H. Godfrin

Publications (5)5.86 Total impact

• Article: Collective excitations in liquid 4He: I. Experiment and presentation of data

  K H Andersen, W G Stirling, R Scherm, A Stunault, B Fak, H Godfrin, A J Dianoux
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  ABSTRACT: We report neutron scattering measurements of the dynamic structure factor S(Q, omega ) of liquid 4He in the collective excitation regime. The use of the IN6 time-of-flight spectrometer at the Institut Laue-Langevin has enabled us to cover the wavevector region from 0.3 to 2.1 AA-1 in a continuous manner with an accurately calibrated energy scale and an energy resolution of approximately 0.1 meV; temperatures between 1.24 and 4.95 K were examined at saturated vapour pressure. In the wavevector region investigated, sharp excitations are seen that are unique to superfluid 4He; it is the purpose of the present paper to examine their temperature dependence and to discuss measurements of the multiphonon continuum scattering at higher energies. At small wavevectors in the 'phonon' region, the excitations are relatively unaffected by the lambda transition, whereas at larger Q a sharp component disappears at or close to Tlambda . The temperature variation of S(Q, omega ) is much more rapid in the superfluid phase than in the normal phase. In paper II of this series, the results for S(Q, omega ) will be compared with several models for the temperature variation of the 4He excitation spectrum.
  Journal of Physics Condensed Matter 12/1998; 6(4):821. · 2.55 Impact Factor
• Article: Temperature Dependence of Spin-Density Fluctuations in Liquid 3He

  B. Fåk, N.H. van Dijk, K. Guckelsberger, H. Godfrin, R. Scherm, H. Schober
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  ABSTRACT: The dynamic structure factor S(Q,E) in normal liquid 3 He, which contains information on both density and spin-density fluctuations, has been measured by inelastic neutron scattering both well below and close to the Fermi temperature. The data extend to smaller wave vectors and energies than covered in earlier experiments, and give a much better determination of the line shape of the spin-density response. Together with the temperature dependence, this allows to discriminate between different theoretical models for the nuclear spin fluctuations, and provides information on the quasiparticle dispersion and effective mass.
  Journal of Low Temperature Physics 12/1997; 110(1):417-424. · 1.19 Impact Factor
• Source

  Available from: tudelft.nl

  Article: Effective mass, spin fluctuations, and zero sound in liquid 3He

  H R Glyde, B. Fak, N.H. van Dijk, H. Godfrin, K Guckelsberger, R Scherm
  Physical Review B - Condensed Matter and Materials Physics, 61 (2).
• Article: Precision determination of S(Q, ω) of liquid 4He as a function of temperature

  K.H. Andersen, W.G. Stirling, R. Scherm, A. Stunault, B. Fåk, H. Godfrin, A.J. Dianoux
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  ABSTRACT: We report high-resolution high-precision measurements of S(Q, ω) of liquid 4He at SVP at a range of temperatures above and below Tλ, covering the wave vector range from 0.3 to 2.1Å-1. The temperature dependence is seen to depend sensitively on Q, the phonon remaining a well-defined excitation above Tλ, while the maxon and roton excitations change abruptly at Tλ, leaving no sharp peak at temperatures above.
  Physica B Condensed Matter · 1.06 Impact Factor
• Article: Black is beautiful: 3He — An experimental challenge to neutron spectroscopy

  K. Guckelsberger, Y. Blanc, A.J. Dianoux, B. Fåk, H. Godfrin, M. Körfer, R. Scherm, K. Sköld
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  ABSTRACT: The integrated design of a spectrometer and sample sysyem for inelastic neutron scattering studies of strongly absorbing 3He and 3He4He mixtures is described.
  Physica B Condensed Matter · 1.06 Impact Factor