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Structure microscopique et dynamique des vortex dans un superfluide dense

Abstract : Vortices study's justification lays in the fact that those former play an important part in quantum turbulence. The Gross-Pitaevskii equation can't be a proper model for superfluid helium, but we can still use it to determine the order parameter of a theoretical superfluid, which has then the maximum amount of properties in common with liquid helium, and in particular, the same dispersion relation, thus gained by modifying the interaction terms.We then make the assumption that all the physical properties of the superfluid are triggered by the existence of the roton minimum, which allows us to calculate the order parameter far from the perturbation created by an axisymmetric rectilinear vortex, using two different methods. At that point, it appears that only two parameters are needed to fully characterize vortex profil.Pomeau-Rica's model offers the possibility to study the superfluid near crystallization and reveals the influence of the roton minimum's shape and depth on oscillations' amplitude. Results are subsequently compared to those given by Reatto's ab initio calculations. In Berloff-Roberts' model, profil displays a strong phase shift, which seems to be a non-physical consequence of the dispersion relation's shape at high frequencies. Energies reckoning leads us to think that oscillations carry a small fraction of the total vortex' energy, meaning that the kinetic energy is dominant.The order parameter for a vortex ring, whose radius is much larger than the interatomic distance, is calculated at zero and nonzero speed. Potential and kinetic energies are estimated and help us obtain the maximal speed reached by such a ring, depending on its radius and finally discussed this speed in regard to the Landau critical speed.
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  • HAL Id : tel-00775920, version 1

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Sophie Villerot. Structure microscopique et dynamique des vortex dans un superfluide dense. Autre [cond-mat.other]. Ecole normale supérieure de lyon - ENS LYON, 2012. Français. ⟨NNT : 2012ENSL0774⟩. ⟨tel-00775920⟩

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