SPECTRAL AND MAGNETIC-PROPERTIES OF ONE-DIMENSIONAL SUPERLATTICES

We investigated the electron con-elation effects in one-dimensional su perlattices composed of free (uncorrelated) and repulsive (correlated) sites, using Lanczos diagonalization of chains of up to ten sites des cribed by a Hubbard-like Hamiltonian. The electronic and magnetic prop erties are shown to depend primarily on the splitting between single-s ite energies for the correlated and uncorrelated orbitals, respectivel y, and on the average electron density in the system. The local moment s and spin-spin correlations are closely related to the changes in the conductivity, and the magnetic properties are enhanced when the insul ating regime is approached. Irrespective of the type of superlattice c onsidered, the local moments form on the correlated orbitals, and may only be induced on single uncorrelated orbitals which separate correla ted clusters. The transition from metallic to insulating behaviour can be qualitatively understood in terms of a strongly correlated model, with two Hubbard subbands due to strong Coulomb interactions accompani ed by a metallic band of uncorrelated states.