ELECTRONIC CORRELATIONS IN ONE-DIMENSIONAL SUPERLATTICES

We consider fermions on a one-dimensional superlattice, represented by a repeated pattern of repulsive (i.e., positive Hubbard U) and free ( i.e., U = 0) sites. Lanczos diagonalization of chains up to 12 sites a t half filling shows that some patterns give rise to a weak form of fr ustration. sufficient to wipe out the spin-density-wave (SDW) correlat ions present in the otherwise homogeneous system. On the other hand, S DW correlations appear for some patterns above half filling, a feature absent in the homogeneous case. Below half filling, the local-moment maxima are displaced from the repulsive to the free sites. The peak in the magnetic structure factor is also shifted from q = pi, for the al ternating configuration when rho = 1/3 and 5/3.