Evidence for Solitons in Conducting Organic Charge-Transfer Crystals

Abstract

Magnetic susceptibility of ${(\mathrm{N}-\mathrm{methylphenazinium})}_x{\mathrm{}\left(\mathrm{phenazine}\right)\mathrm{}}_{1-x}(\mathrm{t}\mathrm{e}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{c}\mathrm{y}\mathrm{a}\mathrm{n}\mathrm{o}\mathrm{q}\mathrm{u}\mathrm{i}\mathrm{n}\mathrm{o}\mathrm{d}\mathrm{i}\mathrm{m}\mathrm{e}-\mathrm{t}\mathrm{h}\mathrm{a}\mathrm{n}\mathrm{i}\mathrm{d}\mathrm{e})$ [${\left(\mathrm{NMP}\right)}_x{\left(\mathrm{Phen}\right)}_{1-x}\left(\mathrm{TCNQ}\right)$] shows the formation of defect states for $0.5\lesssim x\lesssim 0.54$. 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.