The nature of magnetic order and transport properties near surfaces is a topic of great current interest. Here we model metal-insulator interfaces with a multilayer system governed by a tight-binding Hamiltonian in which the interaction is nonzero on one set of adjacent planes and zero on another. As the interface hybridization is tuned, magnetic and metallic properties undergo an evolution that reflects the competition between antiferromagnetism and (Kondo) singlet formation in a scenario similar to that occurring in heavy-fermion materials. For a few-layer system at intermediate hybridization, a Kondo insulating phase results, where magnetic order and conductivity are suppressed in all layers. As more insulating layers are added, magnetic order is restored in all correlated layers except that at the interface. Residual signs of Kondo physics are however evident in the bulk as a substantial reduction of the order parameter in the 2 to 3 layers immediately adjacent to the interfacial one. We find no signature of long-range magnetic order in the metallic layers.

The effect of on-site electron-electron repulsion U in a band insulator is explored for a bilayer Hubbard Hamiltonian with opposite sign hopping in the two sheets. The ground state phase diagram is determined at half-filling in the plane of U and the interplanar hybridization V through a computation of the antiferromagnetic (AF) structure factor, local moments, single particle and spin wave spectra, and spin correlations. Unlike the case of the ionic Hubbard model, no evidence is found for a metallic phase intervening between the Mott and band insulators. Instead, upon increase of U at large V , the behavior of the local moments and of single-particle spectra give quantitative evidence of a crossover to a Mott insulator state preceeding the onset of magnetic order. Our conclusions generalize those of single-site dynamical mean field theory, and show that including interlayer correlations results in an increase of the single particle gap with U .

Determinant Quantum Monte Carlo (DQMC) is used to study the effect of non-zero hopping t f in the "localized" f -band of the periodic Anderson model (PAM) in two dimensions. The low temperature properties are determined in the plane of interband hybridization V and t f at fixed U f and half-filling, including the case when the sign of t f is opposite to that of the conduction band t d . For t f and t d of the same sign, and when t f /t d > (V /4t d ) 2 , the non-interacting system is metallic. We show that a remnant of the band insulator to metal line at U f = 0 persists in the interacting system, manifesting itself as a maximal tendency toward antiferromagnetic correlations at low temperature. In this "optimal" t f region, short range (e.g. near-neighbor) and long-range spin correlations develop at similar temperatures and have comparable magnitude. Both observations are in stark contrast with the situation in the widely studied PAM (t f = 0) and single band Hubbard model, where short range correlations are stronger and develop at higher temperature. The effect that finite t f has on Kondo screening is investigated by considering the evolution of the local density of states for selected t f as a function of V . We use mean field theory as a tool to discriminate those aspects of the physics that are genuinely many-body in character.