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Capillary-wave dynamics and interface structure modulation in binary Bose-Einstein condensate mixtures

Journal Contribution - Journal Article

© 2018 American Physical Society. The localized low-energy interfacial excitations, or interfacial Nambu-Goldstone modes, of phase-segregated binary mixtures of Bose-Einstein condensates are investigated analytically. To this end a double-parabola approximation (DPA) is performed on the Lagrangian density in Gross-Pitaevskii theory for a system in a uniform potential. This DPA entails a model in which analytic expressions are obtained for the excitations underlying capillary waves or ripplons for arbitrary strength K (>1) of the phase segregation. The dispersion relation ω(k) k3/2 is derived directly from the Bogoliubov-de Gennes equations in the limit that the wavelength 2π/k is much larger than the interface width. The proportionality constant in the dispersion relation provides the static interfacial tension. A correction term in ω(k) of order k5/2 is calculated analytically within the DPA model. The combined result is tested against numerical diagonalization of the exact Bogoliubov-de Gennes equations. Satisfactory agreement is obtained in the range of physically relevant wavelengths. The ripplon dispersion relation is relevant to state-of-the-art experiments using (quasi)uniform optical-box traps. Furthermore, within the DPA model explicit expressions are obtained for the structural deformation of the interface due to the passing of the capillary wave. It is found that the amplitude of the wave is enhanced by an amount that is quadratic in the ratio of the phase velocity ω/k to the sound velocity c. For generic mixtures consisting of condensates with unequal healing lengths, an additional modulation is predicted of the common value of the condensate densities at the interface.
Journal: Physical Review A
ISSN: 2469-9926
Issue: 4
Volume: 97
Publication year:2018
BOF-keylabel:yes
IOF-keylabel:yes
BOF-publication weight:1
CSS-citation score:1
Authors:International
Authors from:Higher Education