Violation of the Peierls theorem in graphite chains

Abstract

Vibronic (or Peierls) instabilities in polyacene (PA), polyacenacene (PAA), and polyperylene (PP) are studied, combining tight-binding band-structure computations with rigorous line-group theoretical arguments. Contrary to the current belief, for each of these polymers a static distortion exists, opening a gap that is linear with respect to the distortion amplitude, at the Fermi level. On the other hand, their behavior departs significantly from that of the simple Peierls model. Novel types of symmetry breaking are identified; vibronically active modes are either transverse optical or longitudinal optical. In addition, PA and PAA are predicted to possess two inequivalent but equi-energetic distorted ground-state configurations each. Thus, these polymers can support interphase soliton kinks, which may be of novel (transverse) type. Experimental tests are suggested to check these predictions.