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We report Hall effect measurements performed in the normal phase and at ambient pressure of (TMTSF) 2 ReO 4 and (more anisotropic) (TMTTF) 2 AsF 6 quasi-1D organic conductors. For T>200 K, the Hall coefficient of (TMTSF) 2 ReO 4 is smoothly temperature-dependent, and its value corresponds to a carrier concentration of one hole/unit cell. On the other hand, the Hall coefficient of (TMTTF) 2 AsF 6 is enhanced above 220 K, and the corresponding carrier concentration is almost 100 times lower than the expected one for one hole/unit cell. Our results give evidence for the existence of a high temperature regime above 200 K in (TMTTF)2X salts, where the 1D Luttinger liquid features appear in the transport properties.

We have measured the magnetoresistance and the Hall effect in the spin-density-wave (SDW) state of (TMTSF)_2PF_6 down to 2K and in magnetic fields up to 9T in order to gain an additional insight into the nature of the possible subphases in the SDW state. We have found that the temperature dependent magnetoresistance anisotropy changes below 4K ; this change being maximal for the current in the lowest conductivity direction. The Hall resistivity has showed different magnetic field dependencies for T>4K and T

We report the transverse magnetoresistance measurements at ambient pressure in the organic conductor (TMTTF)2Br in the temperature range between 4.2 K and 40 K and in magnetic fields up to 8.5 T. We have found isotropic, negative and temperature dependent magnetoresistance which becomes negligible, close to 40 K. We interpret the observed behaviour within the picture of strongly correlated quasi-one dimensional systems.

The most comprehensive charge response study of the intrinsically hole doped, spin-chain and spin-ladder composites is overviewed. Results of dc and electric-field-dependent resistivity, low frequency dielectric, and optical spectroscopy in all crystallographic directions are used to build phase diagrams of the underdoped materials (hole count= 6 - y per formula unit, f.u.) and of the fully doped, 6 holes per f.u. The underdoped materials are insulators with hopping transport along the chains, which behave as a one-dimensional disordered system. For the fully doped materials the charge transport switches to the ladders due to transfer of holes from the chains. Two-dimensional (2D) charge-density wave (CDW) ground state is formed, i.e. besides CDW phason response along the ladders for 0 ≤ x ≤ 9, we also found it along the ladder rungs for x ≤ 6. However, CDW sliding conductivity, as observed in the standard CDW materials, is not observed in either of directions. Normal to the ladder planes no CDW response was found, and transport is presumably hopping-like. For the first time in any system, CDW response away from the principal direction was identified. For x > 9 both CDW in ladders and CO in chains are supressed.

Self-organization is a concept, which recognizes a network pattern of organization with internal non-linear relationships as the basic feature of life and reality. In low dimensional systems, self-organized structures could form ordered or glass phases. In the former with the order of commensurability N &#61603 ; ; 3, they can be viewed as topological defects with associated excitations like solitons and charge domain wall pairs or stripes in the background domain structure. In the latter with N &#61603 ; ; 4, they can be recognized as phasons of charge and spin density waves in a disordered background potential. In this lecture I will present some of modalities of self-organized charge response in low dimensional systems, like divers organic and quantum spin systems, studied by the low-frequency (10 mHz &#8211 ; ; 1 MHz) dielectric spectroscopy. Particular emphasis will be devoted to weak ferromagnetic state in &#61547 ; ; -(BEDT-TTF)2Cu[N(CN)2]Cl, Peierls-Mott insulating state in deuterated copper-DCNQI and to charge density wave in Sr14Cu24O41.

We report some results of magnetoresistance, magnetic susceptibility and magnetic anisotropy measurements on single crystals of the two dimensional organic superconductor βL-(BEDT-TTF)2I3 from 4.2 to 300 K. From the c* magnetoresistivity we deduce a value of 0.5 meV for the tight binding transfer integral tc, and show that there is significant conductivity anisotropy (a factor 5) in the a-b plane at low temperatures. A short value of the relaxation time, 0.5 ps at 9 K, indicates that electron transport between planes is becoming incoherent, which may affect the superconducting transition temperature. The static spin susceptibility shows little enhancement relative to the specific heat. The magnetic anisotropy data give evidence for a temperature dependent conduction electron diamagnetism when the magnetic field is perpendicular to the conducting planes., Nous avons mesuré de 300 K à 4,2 K la magnétorésistance, la susceptibilité et l'anisotropie magnétique de monocristaux du supraconducteur organique bi-dimensionnel βL-(BEDT-TTF)2I3. A partir de la magnétorésistance suivant c*, nous avons calculé une valeur de 0,5 meV pour l'intégrale de transfert tc dans un modèle de liaisons fortes. De plus, ces mesures indiquent que l'anisotropie de conductivité dans le plan a-b à basse température est d'un facteur cinq. La faible valeur du temps de relaxation (0,5 ps à 9 K) indique que le transport électronique entre plans devient incohérent, ce qui peut affecter la température de transition supraconductrice. La densité d'états dérivée de la susceptibilité de spin est en bon accord avec celle obtenue par chaleur spécifique. Lorsque le champ magnétique est dirigé perpendiculairement aux plans conducteurs, l'anisotropie magnétique provient en partie d'un diamagnétisme des électrons de conduction qui varie avec la température.

From magnetoresistance measurements in PtFe and PdCo alloys we show that disalignment within the ferromagnetic state begins at concentrations well above a critical concentration at which spin glass order sets in. In PtFe the ferromagnetic to spin glass transition is second order.