Temperature dependence of the electrical conductivity of potassium-doped polyacetylene as a function of pressure and magnetic field

The effects of pressure and magnetic field on the electrical conductivity (σ) of oriented polyacetylene highly doped to the metallic state with potassium, K-(CH${)}_{\mathit{x}}$, has been investigated. The conductivity at 10 kbar is greater than that at ambient pressure by a factor of two, and the temperature dependence is substantially weaker. The power-law temperature dependence of conductivity at ambient pressure, σ(T)∝${\mathit{T}}^{0.57}$, implies that K-(CH${)}_{\mathit{x}}$ is in the critical regime near the metal-insulator boundary. At 10 kbar, σ(T) becomes nearly temperature independent at low temperatures, consistent with pressure driving the system toward a transition into the metallic state. At ambient pressure, it is possible to localize the wave functions of the states near the Fermi level by an external magnetic field; at high fields σ(T) crosses over from the power-law to the exp(-${\mathit{T}}^{\mathrm{-}1/4}$) dependence characteristic of variable range hopping between localized states. Thus, increased pressure tends to delocalize the electronic wave functions, whereas high magnetic fields tend to localize the electronic wave functions.