Irradiation effects on the plasma edge of organic conductors based on TMTSF

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Abstract
The reflectance of 17 irradiated single crystals of (TMTSF)2PF 6, (TMTSF)2AsF6 and (TMTSF) (DMTCNQ) have been measured at room temperature in the frequency range 5 000 to 12 000 cm -1 corresponding to the metallic plasma edge. The reflectance curves have been satisfactorily fitted to a Drude model in order to measure the influence of radiation induced defects on the plasma frequency and the optical relaxation rate. At concentration levels of the order of a few mole % of defects, where the room temperature dc resistivity is known to increase exponentially with dose by an order of magnitude for each new percent of defects, the optical relaxation rate was found to increase linearly with the concentration, with a slope of the order of a few 15-50 % per percent defect The plasma frequency was observed to decrease at a rate of about 5 % per percent defect. This effect, corresponding to a decrease of the number of carriers, is explained by secondary effects related to defects, the principal of which is the change in lattice parameters due to irradiation