Thermodynamique de la réponse électrique dans les isolants de bande - Synchronisation et écho de spin dans une horloge atomique

Abstract : The work exposed in this manuscript covers two distinct topics. The first is about the response of crystalline dielectrics to an external static electric field; it is based on King-Smith, Vanderbilt and Resta modern theory of polarisation. Restricting ourselves to the 1D case, we first describe the Wannier-Stark ladder of a band model with a low-field perturbative approach. We then use this development to derive the thermodynamical response of the band model. We have to modify the usual thermodynamics to account for the unboundedness of the Wannier-Stark spectrum, through the introduction of a local chemical potentiel which ensures local electric neutrality in the crystal. In a last step, we extend our approch to the 2D cas, where new characteristics related to the topic of topological insulators appear.The second topic tackles synchronization and spin-echo in cold atom gases. We study the competition between the spin-echo mechanism and the self-synchronization mechanism which emerges from the identical spin rotation effet (emph{ISRE}). The spin-echo thechnique was built to compensate for some the of dephasing that appears in trapped ultra-cold gases, leading to an increased coherence time for the ensemble. The emph{ISRE} appears in dense atomic clouds where collisions also lead to an increased coherence time. We show that these two mechanism are not always compatible, in particular, their compatibility is based on the relation between the time scales associated to both phenomena.
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Frédéric Combes. Thermodynamique de la réponse électrique dans les isolants de bande - Synchronisation et écho de spin dans une horloge atomique. Matière Condensée [cond-mat]. Université Paris-Saclay, 2018. Français. ⟨NNT : 2018SACLS540⟩. ⟨tel-02137505⟩

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