Radio-Frequency Spectroscopy on Li-K Fermi-Fermi Mixtures

The combination of two different fermionic species offers unprecedented possibilities for research in the field of ultracold strongly interacting Fermi gases. The quantum many-body physics of Fermi-Fermi mixtures offers intriguing new opportunities, both for experimental and theoretical investigations. The prime candidate for realizing such a system is the 6 Li- 40K mixture, on which strong interaction effects were recently observed by the Innsbruck group together with the applicant, who joined the team in April 2010. In this project, we plan to exploit radio-frequency spectroscopy to investigate many-body interactions in the Li-K mixture with interactions tuned into resonance by means of an interspecies Feshbach resonance. We will first characterize the system in the regime of strong population imbalance, by addressing the behavior of attractive and repulsive K Fermi polarons in a degenerate Li Fermi gas. Here, we will measure the energy of attractive K polarons as a function of the Li-K interaction strength, and we will investigate the so far unexplored dynamics of polaron-molecule conversion on the BEC side of a Feshbach resonance. The study of the repulsive branch of the system will help to elucidate the behavior of a many-body state that is poorly known even in the homonuclear case. We will then study the two branches versus the population imbalance. On the attractive branch, we will measure the pairing energy for variable imbalance among the two components, in view of studies of superfluid phases in such a system. Concerning the repulsive branch, the presence of ferromagnetic phases in the polarization/interaction plane of the system will be addressed. A later stage of the project will be dedicated to the application of radio-frequency spectroscopy to probe new regimes which can be realized by means of species-selective potentials, as for example mixed-dimensional or disordered fermionic systems.