Interface response theory of phonons inN-layer superlattices

Abstract
Bulk phonons were obtained previously for a two-layer superlattice, using slab response functions. We show that they can be obtained more directly using bulk response functions and the interface response theory. This new approach enables us to give for the first time a general theory of phonons in N-layer superlattices. As an illustration of the theory, we give a closed-form expression for phonons in three-layer superlattices.