Energy-band structures have been calculated for ?SiR?x polyalkylsilene model compounds, where R indicates an H atom or a CH3 [methyl (Me)] group. A possible Peierls instability has also been investigated theoretically for these polymers. Polyalkylsilene with H-atom or Me side groups have overlapped conduction bands formed of skeleton bands and bands. This band overlapping suppresses the metal-insulator (M-I) transition due to the simple double-bond alternation found in ?CH?x. This band overlapping also causes three types of scattering processes: Two of them are intra--band and intra--band scatterings and the other is inter-band scattering. Inter-band scattering produces a charge-density wave (CDW) having a commensurate wave number of q=/a by dimerizing two skeleton unit cells. Intra--band scattering produces a CDW having an incommensurate wave number of q=2kF. However, this incommensurate CDW is equivalent to an incommensurate CDW with q=2kF produced by intra--band scattering, because the one dimensionality of overlapping band guarantees the relation of kF+kF=/a. The resulting polyalkylsilene tends to have the characteristics of an insulator due to intraband scattering rather than interband scattering. This is because of its orthogonality of overlapping and bands.
ASJC Scopus subject areas
- Condensed Matter Physics