Mortensen, Kell; Tomkiewicz, Yaffa; Bechgaard, Klaus
The anisotropy in the static magnetic susceptibility of bis-tetramethyltetraselenafulvalene hexafluoroarsenate [(TMTSF)2AsF6] has been investigated above and below the metal-to-insulator transition for a range of fields between 0.5 and 30 kG. The results are consistent with the expectations of a ...
Wedl, F.; Walsh, W.M. Jr.; Hauser, J.J.
Preparation and some properties of tetramethyldithiadiselenafulvalene (TMDTDSF) are described. It forms the expected (donor) 2 X salts. Properties of the PF -6 salt are described as well as properties of alloys of the title compound with tetramethyltetraselenafulvalene (TMTSF). (TMDTDSF) 2 PF 6 is a relatively poor conductor even though it is isomorphous with the high-pressure superconductor (TMTSF) 2 PF 6 . The profound difference in properties between these two solids is ascribed to disorder in the arrangement of sulfur and selenium atoms along the donor stacks in (TMDTDSF) 2 PF 6 . Alloying very small amounts of TMDTDSF into (TMTSF) 2 PF 6 causes the metal-to-insulator transition temperature (T/sub MI/) to move up smoothly from 11 K for pure (TMTSF) 2 PF 6 to approx.200 K for pure (TMDTDSF) 2 PF 6 due to increasing disorder as TMDTDSF is incorporated
Jacobsen, Claus Schelde; Tanner, D. B.; Bechgaard, K.
Polarized reflectance measurements from the far infrared to the visible are reported for (TMTSF)2PF6. At low temperatures, both parallel and perpendicular polarizations show plasma edges in the infrared with metallic reflection below these edges, indicating two- or three-dimensional behavior. The...
Parkin, S.S.P.; Ribault, M.; Jerome, D.; Bechgaard, K.
Resistivity against temperature measurements are reported along the high-conductivity a axis of TMTSF 2 ClO 4 , TMTSF 2 SbF 6 and TMTSF 2 TaF 6 , under pressure and as a function of applied magnetic field, that show that all three compounds exhibit superconducting phase transitions near 1 K, when sufficient pressure is applied. TMTSF 2 SbF 6 and TMTSF 2 TaF 6 become superconducting above critical pressures of the order of 10 and 11 kbar respectively whereas a superconducting phase transition in TMTSF 2 ClO 4 is observed at much lower pressures (<3 kbar). The critical pressure above which the sc phase is stabilised can be correlated with the separation between the sheets of TMTSF molecules and anions. (author)
Nakano, M.; Alves, H.; Molinari, A.S.; Ono, S.; Minder, N.; Morpurgo, A.F.
We investigated transport properties of organic heterointerfaces formed by single-crystals of two organic donor-acceptor molecules, tetramethyltetraselenafulvalene and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Whereas the individual crystals have unmeasurably high resistance, the interface exhibits a
Torrance, J. B.; Pedersen, H. J.; Bechgaard, K.
Anomalous microwave absorption has been observed in the organic superconductor TMTSF2AsF6 (TMTSF: tetramethyltetraselenafulvalene) below its metal-nonmetal transition near 12 K. This absorption is unambiguously identified as antiferromagnetic resonance by the excellent agreement between a spin...
Andersen, Jan Rud; Taranko, A. R.; Tomkiewicz, Y.
An organic conductor having a Peierls instability driven by donor stacks is considered. The compound is tetramethyltetraselenafulvalene-2,5-dimethyltetracyanoquinodimethane. Magnetic data confirm that the instability is donor driven. The influence of the unit cell size is examined. The unit cell...... size can be changed by the substitution of sulphur or selenium or by the introduction of methyl groups. The consequences of this are discussed...
Walsh, W.M. Jr.; Wudl, F.; Aharon-Shalom, E.; Rupp, L.W. Jr.; Vandenberg, J.M.; Andres, K.; Torrance, J.B.
Below 5.5 K minimally strained crystals of (TMTSF) 2 ClO 4 (TMTSF: tetramethyltetraselenafulvalene) exhibit vanishing spin-resonance intensity and reduced conductivity at low microwave power. More intense microwave electric fields along the needle axis nonlinearly restore both the resonance signal and the conductivity, indicating the presence of charged spin-density waves. Very anisotropic antiferromagnetic resonances are observed at 1.6 K, confirming that an intinerant spin-density-wave state precedes the onset of superconductivity at 1.3 K
Jacobsen, Claus Schelde; Mortensen, Kell; Andersen, Jan Rud
. Tetramethyltetraselenafulvalene-tetracyano-p-quinodimethane (TMTSeF-TCNQ) has σ(300 K)=1000 Ω-1 cm-1, σmax / σ(300 K)=7, S(300 K)=8μV/K. For tetramethyltetraselenafulvalene-dimethyltetracyano-p-quinodimethane (TMTSeF-DMTCNQ) σ(300 K)=500 Ω-1 cm-1, σmax / σ(300 K)=10, S(300 K)=11 μV/K. The sulphur analogue...... tetramethyltetrathiafulvalene-dimethyltetracyano-p-quinodimethane (TMTTF-DMTCNQ) has σ(300 K)=120 Ω-1 cm-1, σmax / σ(300 K)=3, S(300 K)=-30 μV/K, while for diethyldimethyltetraselenafulvalene-tetracyano-p-quinodimethane (DEDMTSeF-TCNQ) we find σ(300 K)=500 Ω-1 cm-1, σmax / σ(300 K)=9, S(300 K)=18μV/K. S(T) for the selenium......-containing materials is small and metallic above the M-I transitions. S(T) for TMTTF-DMTCNQ is high and negative with only slight temperature dependence above 100 K. TMTTF-DMTCNQ and TMTSeF-DMTCNQ are discussed in terms of a simple model of independent stacks. The transport on the DMTCNQ stacks is found...
Fainchtein, R.; Murphy, J.C.
This paper reports on direct observations of the organic superconductors (tetramethyltetraselenafulvalene) (TMTSF) 2 -PF 6 and (TMTSF) 2 -ClO 4 made in air at room temperature. The samples consisted of single crystals electrochemically grown. Images revealing the molecular structural arrangement along different crystallographic orientations will be presented as well as spectroscopic data related to the electronic density of states. The images reveal a structure made up of flat molecules that stack on top of one another to form columns and are responsible for the quasi-one-dimensional nature of the electrical conductivity. Although both materials have similar crystal structure the differences in the symmetry and orientation of the counter anions are not resolved. Tunneling spectroscopy data at room temperature shows no apparent difference in the electronic density of states of both materials
Spitsina, N G; Bashkin, I V; Meletov, K P
We have studied the pristine C sub 6 sub 0 and its molecular complexes with the organic donors bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF or ET) and tetramethyltetraselenafulvalene (TMTSF) by means of ESR and Raman spectroscopy at high pressure. The important changes in the ESR signal of C sub 6 sub 0 were observed under axial pressure combined with shear deformation. It is shown that the treatment at a anisotropic pressure of 4 GPa results in a reduction in the symmetry of the C sub 6 sub 0 molecule and the formation of radicals. Treatment of the molecular complex of (ET) sub 2 centre dot C sub 6 sub 0 at a pressure of approx 4.5 GPa and a temperature of 150 deg. C leads to the formation of C sub 6 sub 0 dimers. The Raman spectra of the molecular complex C sub 6 sub 0 centre dot TMTSF centre dot 2(CS sub 2) were measured in situ at ambient temperature and pressures up to 9.5 GPa. The pressure behaviour of the Raman peaks reveals singularity at 5.0 +- 0.5 GPa related to the softening and splitting of so...