Metal-insulator transition by suppression of spin fluctuations

We have studied the metal-insulator transition in the antiferromagnetic (AF) two-plane Hubbard model in infinite dimensions as a function of the perpendicular hopping t(perpendicular to) between the two planes. In the weak-coupling regime the system undergoes a transition from a metallic to a band insulating state. For strong coupling, a transition from an AF insulating state to a singlet state occurs at t(perpendicular to)/t approximate to root 2, which is consistent with a competition between intra-and inter-plane Heisenberg exchange. We calculate the spin-correlation functions of the model and show that the picture of a transition to a singlet insulating state remains valid for intermediate coupling, independent of the presence of long-range AF order. The quasiparticle peak continuously disappears due to the suppression of the local spin fluctuations by formation of the coherent singlet state. The transition is accompanied by the opening of a spin gap in the dynamical susceptibility. Copyright (C) EPLA, 2009