In view of the recent experimental facts in the iron-pnictides, we make a proposal that the itinerant electrons and local moments are simultaneously present in such multiband materials. We study a minimal model composed of coupled itinerant electrons
and local moments to illustrate how a consistent explanation of the experimental measurements can be obtained in the leading order approximation. In this mean-field approach, the spin-density-wave (SDW) order and superconducting pairing of the itinerant electrons are not directly driven by the Fermi surface nesting, but are mainly induced by their coupling to the local moments. The presence of the local moments as independent degrees of freedom naturally provides strong pairing strength for superconductivity and also explains the normal-state linear-temperature magnetic susceptibility above the SDW transition temperature. We show that this simple model is supported by various anomalous magnetic properties and isotope effect which are in quantitative agreement with experiments.
In this paper, we analyze the quantum phases of multiple component Bose-Hubbard model in optical superlattices, using a mean-field method, the decoupling approximation. We find that the phase diagrams exhibit complected patterns and regions with vari
ous Charge Density Wave (CDW) for both one- and two- component cases. We also analyze the effective spin dynamics for the two-component case in strong-coupling region at unit filling, and show the possible existence of a Spin Density Wave (SDW) order.
Recent experiments on quantum degenerate gases give an opportunity for simulating strongly-correlated electronic systems in optical lattices. It may shed light on some long-standing puzzles in condensed-matter physics, like the nature of high-tempera
ture superconductivity in cuprates that had baffled people over two decades. It is believed that the two-dimensional fermionic Hubbard model, or t-J model, contains the key to this problem; but the difficulty of unveiling the mystery of a strongly-interacting fermionic system is also generally acknowledged. Here, as a substitute, we systematically analyze the property of bosonic t-J model simulated in optical superlattices near unit-filling. In particular, we show the emergence of a strange topological Fermi liquid with Fermi surfaces from a purely bosonic system. We also discuss the possibility of observing these phenomena in ultracold atom experiments. The result may provide some crucial insights into the origin of high-T_{c} superconductivity.
In this paper, the quantum phase transition between superfluid state and Mott-insulator state is studied based on an extended Bose-Hubbard model with two- and three-body on-site interactions. By employing the mean-field approximation we find the exte
nsion of the insulating lobes and the existence of a fixed point in three dimensional phase space. We investigate the link between experimental parameters and theoretical variables. The possibility to obverse our results through some experimental effects in optically trapped Bose-Einstein Condensates(BEC) is also discussed.
