Abstract
The effects of the superlattice structure along the c-axis on the single particle density of state (DOS) for high temperature superconductors are investigated by considering superlattice systems that consists of metals/insulators and d-wave superconductors (NS/IS superlattices). It is shown that the positions of the quasi-particle peak crucially depend on how the c-axis is modeled. Furthermore, a small current along c-axis can also change the density of state at zero energy, resulting in different behaviors for the the NS superlattice and the IS superlattice.