Suppression of superconductivity by non-magnetic disorder in the organic superconductor (TMTSF)2(ClO4)(1-x)(ReO4)x

We present a study of the superconducting properties (Tc and Hc2) in the solid solution (TMTSF)2(ClO4)(1-x)(ReO4)x with a ReO-4 nominal concentration up to x = 6%. The dramatic suppression of Tc when the residual resistivity is increased upon alloying with no modification of the Fermi surface is the signature of non-conventional superconductivity . This behaviour strongly supports p or d wave pairing in quasi one dimensional organic superconductors. The determination of the electron lifetime in the normal state at low temperature confirms that a single particle Drude model is unable to explain the temperature dependence of the conductivity and that a very narrow zero frequency mode must be taken into account for the interpretation of the transport properties.Comment: Received 26 January 2004 / Received in final form 17 June 2004 / Published online 3 August 200

Approaching the limit of CuII/CuImixed valency in a CuIBr2–N-methylquinoxalinium hybrid compound

A novel 1D hybrid salt (MQ)[CuBr2]∞ (MQ = N-methylquinoxalinium) is reported. Structural, spectroscopic and magnetic investigations reveal a minimal CuII doping of less than 0.1%. However it is not possible to distinguish CuI and CuII. The unusually close packing of the organic moieties and the dark brown colour of the crystals suggest a defect electronic structure

Halogen Bonding Interactions in DDQ Charge Transfer Salts with Iodinated TTFs

International audienceOxidation of 3,4-ethylenedithio-3'-iodo-tetrathiafulvalene (EDT-TTF-I) and 3,4-ethylenedithio-3',4'-diiodo-tetrathiafulvalene (EDT-TTF-I2) with DDQ afforded two different salts formulated as (EDT-TTF-I)(DDQ) and (EDT-TTF-I2)2(DDQ)*(CH3CN), both characterized with a full charge transfer to the DDQ acceptor moiety and by short and linear halogen bonding interactions between the iodine atom as halogen bond donor, and the carbonyl oxygen or the nitrile nitrogen atoms of reduced DDQ

Combining halogen bonding and chirality in a two-dimensional organic metal (EDT-TTF-I2)2(D-camphorsulfonate).H2O.

International audienceA chiral organic conductor with metallic conductivity has been obtained by electrocrystallisation of a diiodotetrathiafulvalene derivative and enantiopure D-camphorsulfonate anion, associated in the solid state by halogen bonding interactions

C--I NC halogen bonding in two polymorphs of the mixed-valence 2:1 charge-transfer salt (EDTTTF- I2)2(TCNQF4), with segregated versus alternated stacks

International audienceOxidation of diiodoethylenedithiotetrathiafulvalene (EDT-TTF-I2), C8H4I2S6, with the strong oxidizer tetrafluorotetracyanoquinodimethane (TCNQF4), C12F4N4, affords, depending on the crystallization solvent, two polymorphs of the 2:1 charge-transfer salt (EDT-TTF-I2)2(TCNQF4), represented as D2A. In both salts, the TCNQF4 is reduced to the radical anion state, and is associated through short C-I...NC halogen bonds to two EDT-TTF-I2 molecules. The two polymorphs differ in the solid-state association of these trimeric D-A-D motifs. In polymorph (I) the trimeric motif is located on an inversion centre, and hence both EDT-TTF-I2 molecules have +0.5 charge. Together with segregation of the TTF and TCNQ derivatives into stacks, this leads to a charge-transfer salt with high conductivity. In polymorph (II) two crystallographically independent EDT-TTF-I2 molecules bear different charges, close to 0 and +1, as deduced from an established correlation between intramolecular bond lengths and charge. Overlap interactions between the halogen-bonded D0-A^{{-}{\bullet}}-D^{{+}{\bullet}} motifs give rise, in a perpendicular direction, to diamagnetic A22- and D0-D22+-D0 entities, where the radical species are paired into the bonding combination of respectively the acceptor LUMOs and donor HOMOs. The strikingly different solid-state organization of the halogen-bonded D-A-D motifs provides an illustrative example of two modes of face-to-face interaction between [pi]-type radicals, into either delocalized, uniform chains with partial charge transfer and conducting behaviour, or localized association of radicals into face-to-face A22- and D22+ dyads

Temperature dependent resistivity under pressure and magnetoresistance data of the organic superconductor (BEDO-TTF)2ReO4(H2O)

The temperature dependence of the resistivity under pressure (up to 6 kbar) of the organic metal (BEDO-TTF)2ReO4(H20) is reported. An increase of the resistivity below 35 K, which is observed at ambient pressure, is already suppressed at 1 kbar. In addition at this pressure the superconducting transition sharpens and the onset temperature of 2.3 K is nearly the same as at ambient pressure. Magnetoresistance data, observed at 1.3 K and 6.7 Tesla show a strong angle dependence. In addition at 1.3 K first SdH -oscillations in the magnetoresistance are found already at such low fields as 5 Tesla

Superconductivity in TTF[Ni(dmit)2]2 films

We report on the observation of a superconducting transition in a fiber-like film of the TTF[Ni(dmit)2]2 phase electrodeposited on silicon substrates. Superconductivity is evidenced by a broad drop of the resistance below 0.8K under the application of a hydrostatic pressure of 7.7 kbar. Zero resistance is not reached due to the contribution of inter-fiber resistance. Superconductivity is confirmed by the application of a magnetic field perpendicular to the plane of the film. The critical field determined on the film is in agreement with that obtained in bulk single crystals

The metallic transport of (TMTSF)_2X organic conductors close to the superconducting phase

Comparing resistivity data of quasi-one dimensional superconductors (TMTSF)_2PF_6 and (TMTSF)_2ClO_4 along the least conducting c*-axis and along the high conductivity a -axis as a function of temperature and pressure, a low temperature regime is observed in which a unique scattering time governs transport along both directions of these anisotropic conductors. However, the pressure dependence of the anisotropy implies a large pressure dependence of the interlayer coupling. This is in agreement with the results of first-principles DFT calculations implying methyl group hyperconjugation in the TMTSF molecule. In this low temperature regime, both materials exhibit for rc a temperature dependence aT + bT^2. Taking into account the strong pressure dependence of the anisotropy, the T-linear rc is found to correlate with the suppression of the superconducting Tc, in close analogy with ra data. This work is revealing the domain of existence of the 3D coherent regime in the generic (TMTSF)_2X phase diagram and provides further support for the correlation between T-linear resistivity and superconductivity in non-conventional superconductors

Combining chirality and hydrogen bonding in methylated ethylenedithio- tetrathiafulvalene primary diamide precursors and radical cation salts

Methyl- and dimethyl-ethylenedithio-tetrathiafulvalene ortho-diamide donors Me-EDT-TTF(CONH2)2 (1a) and DM-EDT- TTF(CONH2)2 (1b) have been prepared by the direct reaction of the corresponding diester precursors with aqueous ammonia solutions. The neutral (rac)-1a, (R)-1a, and (S,S)-1b donors have been characterized by single crystal X-ray diffraction. In the three compounds, which crystallized in the non-centrosymmetric monoclinic space group P21, the amide groups are disordered, yet they form the classical intra-molecular hydrogen bond for such an ortho-diamide motif. Electro- crystallization experiments afforded the mixed valence radical cation salts[(S,S)-1b]2XO4 and [(R,R)-1b]2XO4 (X = Cl, Re) containing four independent donors in the asymmetric unit, with the positive charge localized essentially on two donors, while the two others are neutral. The topology of the organic layer is of β′-type. Single crystal resistivity measurements show semiconducting behavior for [(S,S)-1b]2ClO4 and [(R,R)-1b]2ReO4, with a room temperature conductivity of 5 × 10−5 S cm−1 and activation energies Ea ≈ 3000 K. Tight-binding band structure calculations of extended Hückel type in combination with density functional theory calculations are in agreement with the semiconducting behavior and suggest a localized Mott type semiconductor rather than a band gap semiconductor