Experimental investigations of highly conducting quasi one-dimensional organic charge transfer salts

Experimental investigations discussed involving measurement of electrical conductivity, thermoelectric power, thermal expansivity, spin resonance and magnetic susceptibility, were aimed at characterizing the nature of the quasi one-dimensional electrical transport in TTF-TCNQ and other highly conducting organic charge transfer salts. One particular goal was a clarification of the possible roles of single-particle processes vs. one-dimensional collective effects in the metallic temperature dependence of the conductivity of TTF-TCNQ above 60 K, and in the metal-semiconductor transition at 53 K. Electrical measurements on single-crystal TTF-TCNQ samples indicated a large and strongly temperature-dependent conductivity anisotropy. The possible effects of the large anisotropy on conventional four-probe conductivity measurements were also investigated, and it was found that spurious enhancement of the apparent conductivity by at least a factor of ten could be produced by either misalignment of small contacts or by subtler contact inhomogeneities. A simple experimental check for such enhancement is proposed.