I will report on new results from three experiments on ultracold Fermi gases in Innsbruck.
- In a gas of Li-6 atoms, we have observed "second sound", which is a striking manifestation of the two-component nature of a superfluid. Second sound corresponds to an entropy wave, where the superfluid and the non-superfluid components oscillate in opposite phase, different from ordinary sound ("first sound"), where they oscillate in phase. Our measurements of the second-sound speed allow us to extract the temperature dependence of the superfluid fraction, which in strongly interacting quantum gases has been an inaccessible quantity so far.
- In a mixture of Li-6 and K-40, we have studied atom-dimer interactions by radio-frequency spectroscopy. We have observed an attraction on the repulsive side of the Feshbach resonance, which represents a unique consequence of a few-body phenomenon and only occurs in systems with mass imbalance.
- We have created a degenerate dipolar Fermi gas of 167-Er, demonstrating highly efficient evaporative cooling of a single spin component based on universal dipolar scattering. The experiment reaches exceptionally high number densities along with a remarkable collisional stability, pointing towards new regimes in ultracold Fermi gases.
