Long-wavelength optic vibrations in a superlattice

For a critical examination of the dielectric continuum model as applied to a superlattice, we have introduced a microscopic model, which takes proper account of the long-range Coulomb interaction and yet permits easy solution for the long-wavelength LO and TO modes. With this model, it is shown that such long-wavelength modes approach different limits depending on directions of propagation relative to the axis of the superlattice. This demonstrates that to treat the confined bulklike modes in superlattices as modes of isolated slabs is inadequate.