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Abstract : Large fluctuation effects in one-dimensional conductors prevent the occurrence of metal-insulator transitions at finite temperature. However, in the charge transfer salts of the TTF-TCNQ family, the existence of well defined M-I transitions at T = Tp is attributed to a non zero 3 dimensional coupling. Effects of high pressure on conducting charge transfer salts will be reviewed 1 : i on the low temperature insulating phase, with emphasis on the stabilisation of the metallic phase in the HMTTF-HMTSF-TCNQ structure 2 ; ii on the metallic phase : conductivity, anisotropy, magnetic properties ; iii on the hopping rate τ-1MATH between conducting chains measured by the field dependence of the nuclear relaxation rate 3. We present a unified picture of quasi 1-D conductors based on two parameters : the tunneling interchain coupling tMATH and the intrachain electron scattering time τν. Within this model the electronic properties exhibit a cross-over at T = T* between a high temperature 1-D metallic Fermi surface and a low temperature 3 D semi-metallic surface 4. The validity of this model is corroborated by the temperature dependence of the Hall effect 5, magnetoresistance and susceptibility in HMTSF-TCNQ 6 for which Tp < T* and by pretransitional effects in TTF-TCNQ for which Tp > T* 7.





Autor: D. Jérome

Fuente: https://hal.archives-ouvertes.fr/



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