Abstract
The effect of the superlattice structure along the c-axis on the single particle density of high temperature superconductors is investigated by considering superlattice systems that consists of metals/insulators and d-wave superconductors (NS/IS superlattices). It is shown that the position of quasiparticle peak is sensitive to how one models the c-axis tunneling. For the NS superlattice, the position of the quasiparticle peak can be considerably smaller than the gap value, while for the IS superlattice, the quasiparticle peak always remains at the bulk value so that the whole system behaves like a single superconductor. Furthermore, in the presence of a small current, the density of state at zero energy becomes non-zero for the NS superlattice while it sticks to zero for the IS superlattice. This results in different behaviors in the specific heat measurements, providing a possible way to differentiate between these two models. © 2003 Elsevier Science B.V. All rights reserved.