Dynamics of Quantum Liquids in Con nement, Theory and Experiment
نویسندگان
چکیده
Liquid He immersed in porous media such as aerogel, Vycor, and Geltech silica are excellent examples of a Bosons in disorder and con nement. Of special interest is the impact of disorder on BoseEinstein condensation (BEC), on the elementary excitations of the super uid and on their connection to the super uid properties. Indeed, the modi cations induced by disorder can be used to reveal the interdependence of BEC, the excitations and super uidity. To date, the super uid properties in porous media are much more completely documented than BEC or the excitations. In this talk, we review measurements of the excitations by neutron scattering, focusing particularly on their temperature dependence and the existence of phonon-roton excitations at higher temperatures. The weight of single excitation response at higher temperatures suggests the existence of localized BEC above the super uid-normal transition temperature in porous media. We sketch several recent predictions made for BEC, the excitations, and the super uid properties in disorder. Connections with other \Dirty Bose systems" are made. PACS. 03.75.Kk Dynamic properties of condensates; collective and hydrodynamic excitations, super uid ow { 61.12.Ex Neutron scattering { 67.40.Yv Boson degeneracy and super uidity of He: Impurities and
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