Material properties of low-dimensional charge-transfer salts. I. Charge fluctuations in systems with stronger electronic correlations

Abstract

We derive the necessary electronic conditions allowing for a coincidence of remarkable charge fluctuations 〈(Δ n i 2 )〉 and strong electronic correlations in quasi one-dimensional synthetic metals. The 〈(Δ n i 2)〉 curves show maxima for localized electrons in the case of on-site (intramonomer) electron densities of 0.5 and 1.5, respectively. The formation of an insulating Mott state with completely suppressed fluctuations is thereby prevented. Only one maximum in the 〈Δ n i 2〉 curve for an on-site density of one is found in the independent-particle limit as well as for weaker correlated electrons. The strength of the interatomic correlations of the conduction electrons is characterized by two quantities, Δ i and Σ i, measuring the reduction of the charge fluctuations in the correlated ground state. The phase diagrams of the quasi-one-dimensional metals are critically discussed. It is shown that electron-electron Umklapp-scattering leads to an enhancement in the charge-density wave response function. The Peierls transition temperature T P is enhanced correspondingly. The many-particle effects are studied by a local ansatz, the modification of T P as a function of the correlation strength by the renormalization group approach. The theoretical findings are compared with available experimental results on organic and organometallic materials.