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Nuclear relaxation and antiferromagnetic critical effects in organic conductors
No full textInternational audienceNuclear relaxation and antiferromagnetic critical effects in organic conductor
INFLUENCE OF THE DISORDER POTENTIAL OF THE ANIONS ON THE GROUND STATE OF THE ORGANIC ALLOY (TMTSF)<sub>2</sub>(CIO<sub>4</sub>)<sub>1-x</sub>(Re0<sub>4</sub>)<sub>x</sub>
No full textInternational audienceRésume -Nous présentons une étude expérimentale de l'alliage organique (TMTSF)2 ( cln 4)l-x( Re0 4)• Les résultats montrent l'influence importante des impuretés non-magnétiques sur le comportement à basse température.</div
Organic Superconductors
No full textInternational audienceThe ability to carry an electric current without resistance had been known only in metals. Now superconductivity is seen in organic crystals made up of Rat molecules in zigzag stacks by Klaus Bechgaard and Denis] erome</div
Measurements of thermal resistance of thin brittle samples under high pressure
No full textInternational audienceAn accurate method for mesauring the thermal resistance of small brittle samples of unusual geometry is developed. The method makes use of a thermal potentiometer which compares the temperature gradients in investigated and reference samples. The application of the method to measurement of the thermal resistance of quasi-one-dimensional conductors under normal and high pressures (up to 1.2 GPa (12 kbars)) is described
Periodic lattice distortions and charge density waves in one-and two-dimensional metals
No full textInternational audienceAt low temperatures, low-dimensional metals are commonly found to exhibit superlattices incommensurate with the primitive lattice (periodic lattice distortion coupled to charge density waves, PLD-CDW). Transitions to such states are driven by strong electronphonon coupling and favoured by the particular forms of the Fermi surface of these metals. Experimental investigations of the structural distortions, and of the changes in electronic structure around the Fermi level produced by the PLD-CDW state, will be discussed for the layered dichalcogenides, the linear chain platinum complex KCP, and the organic charge transfer salts
Periodic lattice distortions and charge density waves in one-and two-dimensional metals
No full textInternational audienceAt low temperatures, low-dimensional metals are commonly found to exhibit superlattices incommensurate with the primitive lattice (periodic lattice distortion coupled to charge density waves, PLD-CDW). Transitions to such states are driven by strong electronphonon coupling and favoured by the particular forms of the Fermi surface of these metals. Experimental investigations of the structural distortions, and of the changes in electronic structure around the Fermi level produced by the PLD-CDW state, will be discussed for the layered dichalcogenides, the linear chain platinum complex KCP, and the organic charge transfer salts.</div
ELECTRONIC PROPERTIES OF TTF-TCNQ : A CONNECTION BETWEEN THEORY AND EXPERIMENT
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NMR study on a 2H-NbSe2 single crystal: A microscopic investigation of the charge density waves state?
No full textInternational audienceWe present a pulsed NMR study on a single crystal of 2H-NbSe, at atmospheric pressure and under hydrostatic pressure of 21 kbar in the temperature range 4.2-273 K. Analysis of Knight shift (KS) and nuclear spin-lattice relaxation (NSLR) time data in the normal state are consistent with N(&) = 2.4 stateslevspin and an admixture of40 % of d,, and dxZ -p wavefunctions in the dZ2 band. The product TIT = 500 lOOms K was found constant in the temperature range 4.2-77 K and pressure independent; measurements at the 'magic angle' indicate an orbital contribution (TIT)-' Y 0.9 0.9(s K)-'. The pressure dependence of KS and the electric field gradient tensor (EFG) were respectively found to be: i I n K , a l n q = 5 + 1 and -= 3 & 0.5. Bln V a h v Our results are consistent with the onset of incommensurate charge density waves (ICDW) at To = 33 K at P = 1 bar and To = 26 K at 21 kbar. Below To, the lineshapes of the m + m -1 transitionsagree witha local distribution o f w a n d ~~c r e s p e c t i n g the symmetry ofa tripleIcDw with a maximum value of 9 % for the redistribution of conduction electrons within an atomic cell. Above To, nuclear spin-spin relaxation measurements demonstrate that the observed pretransitional broadening of the lines is due to static CDW fluctuations, induced by impurities
Etude de l'organisation des ions sodium dans l'alumine beta par résonance magnétique nucléaire
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NMR study of the quasi one dimensional conductor K2Pt(CN)4Br0.33H2O
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