Transverse and longitudinal resistivities of pure and irradiated TMTSF-DMTCNQ

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Abstract
The conductivity of TMTSF-DMTCNQ has been measured along the main axis of the crystal as a function of temperature and irradiation dose. At room temperature the anisotropies decrease with irradiation due to the defects cutting the conducting chains into decoupled segments. A quite satisfactory fit of all the dose and temperature curves in the longitudinal and transverse directions has been obtained with a law accounting for the chain segmentation and for the transverse hopping from segment to segment. The model contains only two parameters and allows a direct determination of the defect concentrations. At low temperature (21 K) the anisotropies increase with irradiation dose up to a defect concentration where the Peierls transition has been smeared out of the resistivity vs. temperature curves. When the anisotropy values are those of the metallic state the anisotropies decrease with dose as in the case of room temperature irradiations. Our model describing the effects of irradiation on the resistivity of quasi one-dimensional systems is extended to the case of very large anisotropies (several thousands) and recent interesting results in Qn(TCNQ)2 are discussed