Impact of structural defects on the localized acoustic wave in superlattices

We investigate theoretically the properties of the localized folded acoustic modes in triple-constitution Nb/Fe/Cu superlattice (SL) with a structural defect layer by using a transfer-matrix method. We find that the existence, characteristics, and transmission properties of the localized acoustic modes sensitively depend on structural parameters and material nature of the SL. We demonstrate in detail the correlations between the localized folded acoustic modes inside the minigaps of the infinite SL with structural defect layer and the resonant transmission peaks in dips of the finite SL. A good coincidence between the modes and the peaks is found. This provides a theoretical basis for experimental observation of the localized acoustic modes in SLs via acoustic-phonon transmission experiments