Excitations of modulated crystals near the commensurate-incommensurate transition

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Abstract
The discommensuration (i.e., domain wall) lattice which appears when a modulated crystal (e.g., a crystal containing a charge or spin-density wave, etc.) undergoes a commensurate-incommensurate transition can introduce many closely spaced narrow gaps in the commensurate-state phonon and electron band structures. The locations of these narrow band gaps and the conditions under which they occur and are observable is discussed. Application to various incommensurate systems, including doped polyacetylene, is also discussed. In the case of doped polyacetylene, this band and gap structure may play an important role in the occurrence of a metal-insulation transition.