Non liquide de Fermi dans les conducteurs organiques unidimensionnels
Résumé
This thesis provides new insight into the role of the finite coupling between 1D chains when it comes to restore a conventional Fermi liquid . An efficient way to tune continuously the dimensionality is for instance by mean of hydrostatic pressure which varies the transverse transfer integrals between molecular stacks. Transport experiments have been performed on the quasi 1D organic conductor TMTTF2PF6. We have observed a reduction of the Mott gap and a suppression of the onset temperature of the 3D ordered antiferromagnetic phase. Using the temperature dependence of the incoherent transverse conductivity along the weakest conductivity axis c we are able to study the physics of the a-b planes. The c-axis resistivity exhibits an insulating behaviour down to 100K where it passes through a maximum. The high temperature regime has been ascribed to a Luttinger liquid behaviour with a power law dependence in the density of quasiparticle states. It is also argued that the Mott gap observed in the optical spectrum might seriously affect the transverse transport response.. The transport anisotropy in the a-b planes is consistent with a restoration of the Fermi liquid picture below 10K. As temperature is lowered, the Luttinger description breaks down below 100K and a marginal FL picture with finite quasiparticle lifetimes becomes more appropriate. A conventional FL is eventually recovered below 10K. Hall effect measurements have been performed at ambient pressure on TMTSF2PF6 between 14 and 330K. The Hall signal smoothly decreases down to a local minimum around 130K before rising again upon cooling down to 50K. Below 50K, the Hall signal is influenced by the incipient spin density wave transition occuring at 12K. Between 330 and 130K, the temperature dependence of the Hall voltage should be ascribed to the small fraction of quasiparticles which are left in the Luttinger liquid while below 130K our experiement give some indication of the behaviour of the Hall voltage for a 2D electon gas. A reinvestigation of the field-temperature phase diagram of TMTSF2ClO4 provides strong clues for a closed N=1 domain between 17T and 28T.
Cette thèse étudie le passage liquide de Luttinger liquide de Fermi au moyen de l'application d'une pression hydrostatique dans le conducteur organique quasi unidimensionnel TMTSF2PF6. La dépendance en température de la résistivité le long the l'axe de moindre conductivité fait apparaître un régime haute température qui s'interpréter par des chaînes de Luttinger alors qu'au dessous de 100K le système évolue vers un régime de chaînes couplés avec une physique de type liquide de Fermi.Ce modèle est aussi confirmé par l'étude de l'effet Hall dans le même composé.