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Etude par diffusion de neutrons des proprietes dynamiques de l'helium liquide confine dans des milieux poreux

Abstract : The study of liquid helium confined into porous materials should allow for a better understanding of the relation between superfluidity and Bose-Einstein condensation, lacking, at present, o f a satisfactory theoretical description. Experiments on confined liquid helium are quite difficult and samples should be prepared very carefully. One should know at best the confining material characteristics and should control the actual filling status of the porous sample. To achieve this condition, we added an experimental stage to the procedure commonly used in the studies conducted insofar. We conducted helium adsorption isotherms on each porous sample supposed to be used a s a confining sample. In this way we were able to know, with an high degree of precision, the amount of helium necessary to fill the porous sample. We also get information on macroscopic phenomena occurring during the filling procedure. Some experimental tricks have been used in order to avoid condensation of liquid helium into the injection capillary. Two inelastic neutron scattering techniques have been used in order to get information respectively on the mean kinetic energy per particle and on the elementary excitations spectrum. The kinetic energy measurements showed that confinement is responsible for a rise in this quantity. The elementary excitations measurements showed a correspondence between the capillary condensation process (detected by helium adsorption isotherms measurements) and the presence of elementa ry excitations typical of the liquid helium. Moreover, the long-wavelenght elementary excitations are found to be perturbed in a way compatible with the system geometry. An intrinsic (at T=0.4 K) width of the roton peak is also found.
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https://tel.archives-ouvertes.fr/tel-00006127
Contributor : Francesco Albergamo <>
Submitted on : Saturday, May 22, 2004 - 10:54:38 AM
Last modification on : Friday, March 5, 2021 - 3:01:57 PM
Long-term archiving on: : Friday, April 2, 2010 - 8:34:12 PM

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Francesco Albergamo. Etude par diffusion de neutrons des proprietes dynamiques de l'helium liquide confine dans des milieux poreux. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2001. Français. ⟨tel-00006127⟩

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