The theory of structurally incommensurate systems. III. The fluctuation spectrum of incommensurate phases

Abstract

For pt.II see ibid., vol.11, no.17, p.3591 (1978). The authors discussed the nature of the excitation spectrum of a structurally incommensurate phase, both when the displacement field is describable by a single Fourier component and when it may be described in terms of an array of phase solitons. In each case they established the character of the Goldstone phase mode, and in the latter case they found an additional phase excitation whose properties merge into those of a phase mode in the commensurate structure as the 'lock-in' phase boundary is approached. They examined phase mode-acoustic mode interaction and give a brief discussion of phase mode pinning.