  We study correlation effects on the transport through a quantum dot
superlattice using a two-dimensional Hubbard model connected to two
noninteracting leads. To calculate the zero-temperature conductance away from
half-filling, we have used the non-magnetic solution of the Hartree-Fock
approximation for the unperturbed Green's function, and then take into account
the electron correlation beyond the mean field theory through the second-order
self-energy corrections with respect to the residual interaction. When the
value of the onsite potential $\epsilon_d$ or the repulsion $U$ is changed, the
conductance shows a number of peaks corresponding to the resonance states
passing through the Fermi energy. The behavior of the resonance states for
correlated electrons can be investigated using the eigenvalue of the effective
Hamiltonian for a quasi-particle of a local Fermi liquid. We calculate the
eigenvalue using the second-order self-energy, and show explicitly that it can
be compared with the conductance peak.
