Acoustic-phonon cavity modes in one-dimensional multilayered elastic structures

摘要

We theoretically study "cavity" phonons, i.e., acoustic phonons localized in a foreign layer (a cavity layer) embedded in a periodic one-dimensional superlattice (SL) in the isotropic, continuum approximation. To find the eigenfrequencies of the cavity modes we develop a formulation based on the transfer matrix and Green's function methods and apply it to the case where the confined phonons propagate along the layer interfaces. These cavity phonons are predicted to exist for both the coupled longitudinal and transverse acoustic mode (the sagittal mode) and the single mode with pure transverse polarization (the shear-horizontal mode). Numerical examples are presented for periodic Al/W multilayered structures with a Ag cavity layer and GaAs/AlAs SLs with an Al_(0.8)Ga_(0.2)As layer. Finite-difference time-domain calculations for phonon packet propagation are also conducted to directly illustrate the existence of the confined cavity modes and also to confirm the validity of our formulation.