A model for electrical conductivity in (TMTSF)2ClO4, (TMTSF)2ReO4 and related materials

To describe quantitatively the diverse variations of the temperature-dependent electrical conductivities of tetramethyltetraselenafulvenium (TMTSF) salts, a model based on small Fermi (E_f) and small gap (E_g − E_f) energies and T⁻ⁿ dependence of scattering is presented. The difference between the conductivities of quenched and slowly cooled (TMTSF)₂ClO₄ is described by different values of E_f and E_g − E_f in the two cases. The model illustrates, in terms of variables E_f and E_g − E_f, the effect of pressure on the metal-insulator transition in (TMTSF)₂ReO₄, for example, and indicates a relation between E_f and E_g − E_f at the onset of superconductivity.     

Role of anion ordering in the coexistence of spin-density-wave and superconductivity in (TMTSF)2ClO4

Using various transport and magnetotransport probes, we study the coexistence of spin-density wave and superconductor states in (TMTSF)₂ClO₄ at various degrees of ClO₄ anions ordering. In the two-phase complex state when both superconductivity and spin-density wave are observed in transport, we find prehistory effects, enhancement of the superconducting critical field, and strong spatial anisotropy of the superconducting state. These features are inconsistent with the conventional model of structural inhomogeneities produced by anion ordering transition. We reveal instead that superconductor and spin-density wave regions overlap on the temperature—dimerization gap V phase diagram, where V is varied by anion ordering. The effect of anion ordering on (TMTSF)₂ClO₄ properties is thus analogous to that of pressure on (TMTSF)₂X (X = PF₆ or AsF₆), thereby unifying general picture of the coexistence of superconductivity and spin-density wave in these compounds.     

Magneto-electrogyration in cubic Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2

The simultaneous application of electric and magnetic fields on single crystals of Sr-, Ba-and Pb-dinitrate yields an additional term to the pure electrogyration and Faraday effect. The symmetric part of the fourth-rank tensor of this magneto-electrogyration has been completely determined with the aid of a high-resolution computer-aided polarimetric device. In Pb(NO₃)₂ a maximum magneto-electrogyration of about 10% of the magnitude of electrogyration is observed when a magnetic field of 1000 kA/m (1.2 Tesla) is applied along [111]. The effects in Sr(NO₃)₂ and Ba(NO₃)₂ are much smaller. Index of refraction, electrogyration, Faraday effect, and the new magneto-electrogyration obey the same sequence: Pb(NO₃)₂ > Ba(NO₃)₂ > Sr(NO₃)₂.     

Superconducting state of the organic conductor (TMTSF)2ClO4

(TMTSF)2ClO4 is a quasi-one-dimensional organic conductor and superconductor with Tc=1.4 K, and one of at least two Bechgaard salts observed to have upper critical fields far exceeding the paramagnetic limit. Nevertheless, the 77Se NMR Knight shift at low fields reveals a decrease in spin susceptibility chi(s) consistent with singlet spin pairing. The field dependence of the spin-lattice relaxation rate at 100 mK exhibits a sharp crossover (or phase transition) at a field Hs approximately 15 kOe, to a regime where chi(s) is close to the normal state value, even though Hc2> Hs.     

Oscillatory magnetoresistance in the field-induced SDW state in (TMTSF)2 ClO4

The transverse magnetoresistance of (TMTSF)₂ ClO₄ was measured in pulsed high magnetic fields up to 35 T at T = 1.8−-4.2K for studying the field-induced spin density wave (FISDW) phase. In addition to a structure corresponding to the threshold field B_th (_T) of the FISDW phase, we found two temperature dependent structures in higher field range at 15–17 and 22–25 T, respectively. Moreover, Shubnikov-de Haas type oscillations with smaller period were also observed superposing on the structures. It was found that the peak positions of the oscillation are independent of temperature, whereas their amplitude changes discontinuously at the structures.     

Calculation of the vibrations of [UO2(NO3)3] in rubidium uranyl nitrate

Journal of Applied Spectroscopy -     

Microwave transport approach to the coherence of interchain hopping in (TMTSF)2PF6

We report a microwave study of the longitudinal and transverse transport properties of the quasi-one-dimensional organic conductor (TMTSF)₂PF₆ in its normal phase. The contactless technique have provided a direct measurement of the temperature profile of the resistivity along the b' direction and in magnetic fields up to 14 T. A characteristic energy scale ( K) has been observed which delimits a transient regime from an insulating to a metallic behavior. This anomalous profile is discussed in terms of the onset of coherent transport properties along the b' direction below 40 K. This is also supported by the observation of a finite longitudinal and transverse magnetoresistances only below 40 K, indicative of a two-dimensional regime. Below T_x, however, strong deviations with respect to a Fermi liquid behavior are evidenced. Received 27 January 1999