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Dynamique de spin dans l'hélium 3 superfluide : influence du désordre et condensation Bose-Einstein de magnons

Abstract : The phenomenon of coherent precession of magnetization in superfluid helium 3 was discovered in 1984. It is characterized by the free precession of the magnetization of the superfluid on very long timescales (up to hours). This phenomenon is a signature of spin superfluidity, the magnetic analogue of superconductivity or superfluidity. Spin superfluidity can be described in terms of Bose-Einstein condensation the magnetic excitations of the superfluid: the magnons. This formalism makes it possible to determine easily the conditions in which such a condensation can appear in the different phases of superfluid helium 3. This work shows how the use of anisotropic aerogel permitted us to manipulate the order parameter of the superfluid and thus to obtain new phases in which the Bose-Einstein condensation of magnons can be observed. We were able to study experimentally the coherent precession of magnetization in these new phases. We also studied the influence of the aerogel on the superfluid transition. Finally, we detail how one can obtain the coherent precession of magnetization on different levels of a potential well for magnons.
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Pierre Hunger. Dynamique de spin dans l'hélium 3 superfluide : influence du désordre et condensation Bose-Einstein de magnons. Physique [physics]. Université de Grenoble, 2011. Français. ⟨NNT : 2011GRENY075⟩. ⟨tel-00698466⟩

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