Hydrodynamic Expansion of a Strongly Interacting Fermi-Fermi Mixture

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We report on the expansion of a Fermi-Fermi mixture of Li-6 and K-40 atoms under conditions of strong interactions realized near the center of an interspecies Feshbach resonance.

• We observe two different phenomena of hydrodynamic behavior.
• The first one is the well-known inversion of the aspect ratio.
• The second one is a collective expansion, where both species stick together and despite of their different masses expand jointly.