Probing Interaction-Induced Ferromagnetism in Optical Superlattices*

We analyze how to use ultracold fermionic atoms loaded in optical superlattices for a controllable preparation and detection of interaction-induced ferromagnetism. First, we discuss how to experimentally achieve Nagaoka ferromagnetism in an array of isolated plaquettes (four lattice sites arranged in a square). Next, we allow for weak interplaquette tunneling and analyze the occurrence of itinerant ferromagnetism. Since ferromagnetism is unstable in the presence of weak interplaquette couplings, we propose to mediate long-range ferromagnetic correlations via double-exchange processes by exciting atoms to an excited vibrational band. We calculate the phase diagram of the two-band plaquette array and discuss conditions for the stability and robustness of the ferromagnetic phases in this system. Experimental implementations of the proposed schemes are discussed.