Abstract
The normal modes of vibration in an ionic crystal of finite thickness are found both by using lattice dynamics and by using electrodynamics, and neglecting retardation. If the wavelength is much larger than the lattice parameter, both methods give coupled integral equations involving the ionic displacements and the normal-mode frequencies. There are two classes of normal modes; those with an oscillatory spatial dependence and frequencies equal to and , the usual transverse optical (TO) and longitudinal optical (LO) frequencies at in an infinite crystal, and those with an exponential dependence on distance across the slab and frequencies between and . A qualitative connection between the normal modes and optical absorption in a slab is presented.
- Received 1 July 1965
DOI:https://doi.org/10.1103/PhysRev.140.A2076
©1965 American Physical Society