Fermionic Atoms with Tunable Interactions in a 3d Optical Lattice

The exploration of quantum degenerate gases of fermionic atoms is driven by the ambition to gain deeper insight into long-standing problems of quantum many-body physics. So far, however, the analogy to an electron gas in a solid is limited since there the electrons experience a periodic lattice potential. The lattice structure is in fact a key ingredient for most models describing quantum many-body phenomena in materials. We access this regime by preparing a degenerate atomic Fermi gas in the crystal structure of an optical lattice. In our experiment we load a noninteracting gas of K atoms into a three-dimensional optical lattice with simple cubic symmetry and directly image the Fermi surfaces. Gradual filling of the lattice transforms the system from a normal state into a band insulator. Previous experiments with far-detuned three-dimensional optical lattices were always carried out with bosonic atoms, and experiments with fermions were restricted to a single standing wave. Interactions in the atomic Fermi gas can be tuned by using a Feshbach resonance between different spin components of the gas. By ramping the magnetic field into vicinity of the resonance, we increase the interactions between two particles residing on the same site of the lattice. In this manner