Evidence for Solitons in Conducting Organic Charge-Transfer Crystals

Abstract

Magnetic susceptibility of ${(\mathrm{N}\ensuremath{-}\mathrm{methylphenazinium})}_{x}{(\mathrm{phenazine})}_{1\ensuremath{-}x}(\mathrm{t}\mathrm{e}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{c}\mathrm{y}\mathrm{a}\mathrm{n}\mathrm{o}\mathrm{q}\mathrm{u}\mathrm{i}\mathrm{n}\mathrm{o}\mathrm{d}\mathrm{i}\mathrm{m}\mathrm{e}\ensuremath{-}\mathrm{t}\mathrm{h}\mathrm{a}\mathrm{n}\mathrm{i}\mathrm{d}\mathrm{e})$ [${(\mathrm{NMP})}_{x}{(\mathrm{Phen})}_{1\ensuremath{-}x}(\mathrm{TCNQ})$] shows the formation of defect states for $0.5\ensuremath{\lesssim}x\ensuremath{\lesssim}0.54$. Diffuse x-ray scattering and $g$-value studies indicate that these defects are solitons formed in the highly correlated quasi-one-dimensional system that occurs near the quarter-filled-band limit. A model for the decrease in the energy gap in the presence of large numbers of solitons is proposed to explain the excess conductivity.