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Accueil > FR > Recherche > Physique des Atomes Froids > Séminaire du groupe

Samuel Lellouch (Lab. Charles Fabry, Institut d’Optique), 20 juin 2014

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20 juin 2014 : Propagation of Collective Pair Excitations in Disordered Bose Superfluids

Collective excitations govern most dynamical properties of many-body quantum systems, such as propagation of correlations and thermalization processes. In disordered systems, the transport properties of collective excitations may however be strongly altered, mainly due to Anderson localization. The case of interacting bosons is expected to be particularly involved, since repulsive interactions in Bose systems can compete or cooperate with disorder, inducing nontrivial localization effects. In this talk, we will discuss the effect of disorder on the propagation of collective excitations in a disordered Bose superfluid in dimension d>1. We incorporate local density depletion induced by strong disorder at the mean field level, and formulate the transport of the excitations in terms of a screened scattering problem. We show that the competition of disorder, screening, and density depletion induces a strongly nonmonotonic energy dependence of the disorder parameter, which governs the localization behavior. While in low dimensions, all excitations are localized, we find that in three dimensions, the excitation spectrum can split into alternating bands of localized and extended states, with up to three mobility edges. Implications on experiments with disordered ultracold atoms are discussed.