Fermi-Fermi quantum many-body systems in optical lattices

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Spin mixtures of ultracold fermionic atoms have provided a unique model system for key phenomena in fermionic strongly interacting quantum many-body systems such as Fermion pairing and Fermi superfluidity. So far, the majority of the experiments have been based on spin mixtures of the same fermionic species, although experiments have started to investigate new degrees of freedom - such as spin imbalance - to explore novel superfluid phases.In this research project, we plan to realize and experimentally establish mixtures of two different fermionic atomic species as novel quantum many-body systems. Key goals in this context are to elucidate the role of mass difference on pairing phenomena and superfluid properties in fermionic quantum systems. Unmatched Fermi surfaces are expected to lead to novel quantum phases such as the FFLO (Fulde-Ferrell-Larkin-Ovchinnikov) phase and breached pair superfluidity. Weakly bound dimers of heavy and light atoms are predicted to strongly interact with each other by exchanging light atoms. This can even lead to the formation of a crystalline phase for large mass ratio. From the few-body point of view, mass-imbalanced fermionic mixtures are of particular interest in view of Efimov physics and the possibility of long-lived trimer states.Based on the setup of a new apparatus, the work within this research project will focus on the investigation of quantum degenerate two-species mixtures of fermionic 6Li and 40K atoms in three dimensional optical lattices. We will develop techniques to load two different fermionic species into optical lattices to gain precise control over the filling factor of fermions in the lattice – an essential control parameter for lattice based experiments. Together with tunability of interactions based on Feshbach resonances and the tunability of the effective mass ratio between the two fermionic species, this will allow us to engineer a wide variety of quantum phases in the optical lattice. Our goal is to study the quantum phases in such a massimbalanced mixture which are mainly described within the Fermi-Hubbard model for a massimbalanced fermionic mixture, e.g. band and Mott insulators phases, magnetically ordered phases and superfluid phases. This experimental project will be directly related to theoretical work planned in T1 (U. Schollwöck), T2 (W. Hofstetter), and T3 (W. Zwerger), it will be complementary to the experimental studies on Fermi-Bose mixtures performed within E1 (I. Bloch) and E2 (K. Sengstock), and the study of homogeneous Fermi-Fermi mixtures within E3 (K. Dieckmann).