Band structure of metallictrans-polyacetylene with alkali-metal doping

Abstract

For the average doping 〈y〉>0.4%, trans-polyacetylene is a mixture of heavily doped, ordered regions and weakly doped (∼0.4%) disordered regions. The sharp increase in magnetic susceptibility that marks the insulator-metal transition is consistent with there still being a small gap in the heavily doped regions or with these regions being metallic. The temperature dependence of the resistivity, although dominated by the weakly doped regions, indicates that in some of the most highly doped samples the heavily doped regions are metallic. To determine whether we can account for metallic behavior, we have calculated the band structure of a heavily doped polyacetylene chain with the electrons in soliton states, as indicated experimentally, taking into account the Coulomb potential of the doping ions and solitons on surrounding chains. The lattice structure used was that determined by x rays for stage-1 potassium-doped polyacetylene. Because the arrangement of the solitons relative to the dopants is unknown, we used two different arrangements: a symmetric one and a staggered one.