Density of States and Hopping Conductivity in Nearly Metallic Polyacetylene

Abstract

Nearly metallic polyacetylene doped to the level, y, of -0.01 to 0.05 acceptors or donors per carbon has a high, “nearly metallic” conductivity yet susceptibility very much less than the metallic value. We present here the results of an extensive study of the transport properties of this regime coordinated with magnetic, optical and structural experiments, using ClO₄ ⁻ and l₃ ⁻ doped (CH)_x. We conclude that for all samples studied, the charge conduction is via three dimensional variable range hopping among states near the Fermi level, ^cF. The variation of the density of states, N(ϵ), near ϵ_F, is measured using susceptibility, and shown to determine the detailed transport behavior. Our results are in agreement with the transition to an incommensurate Peierls semiconductor for higher doping levels, with disorder leading to a gapless condition.