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The electronic state of (TMTTF) 2 SbF 6 was investigated by the 1 H and 13 C NMR measurements. The temperature dependence of T 1 −1 in 1 H NMR shows a sharp peak associated with the antiferromagnetic transition at T AF =6 K. The temperature dependence of T 1 −1 is described by the power law T 2.4 below T AF . This suggests the nodal gapless spin wave excitation in antiferromagnetic phase. In 13 C NMR, two sharp peaks at high temperature region, associated with the inner and the outer carbon sites in TMTTF dimer, split into four peaks below 150 K. It indicates that the charge disproportionation occurs. The degree of charge disproportionation Δ ρ is estimated as (0.25±0.09) e from the chemical shift difference. This value of Δ ρ is consistent with that obtained from the infrared spectroscopy. In the antiferromagnetic state (AFI), the observed line shape is well fitted by eight Lorentzian peaks. This suggests that the charge order with the same degree still remains in the AF state. From the line assignment, the AF staggered spin amplitude is obtained as 0.70 μ B and 0.24 μ B at the charge rich and the poor sites, respectively. These values corresponding to almost 1 μ B per dimer are quite different from 0.11 μ B of another AF (AFII) state in (TMTTF) 2 Br with effective higher pressure. As a result, it is understood that the antiferromagnetic staggered spin order is stabilized on the CO state in the AFI phase of (TMTTF) 2 SbF 6 .

We performed the STM Spectroscopy (STS) measurement on organic superconductor deuterated κ-(ET-d[3,3])2Cu[N(CN) 2 ]Br to clarify the mechanism of superconductivity. The mechanism of superconductivity in κ-ET2X is predicted as the spin fluctuation mechanism where the gap symmetry changes from d x 2 − y 2 to dxy with increasing the electron correlation. In previous STS measurements, we found that d[2,2]-Br, d[0,0]-Br and Cu(NCS)2 were d-wave superconductors and the symmetry was described by the d x 2 − y 2 . The electron correlation of these salts is still weak in the frame of the spin fluctuation model. So, we investigated the d[3,3]-Br which located at stronger electron correlation region than the previously studied salts by the STS. We also investigated the STS on the cut lateral surfaces by the focused ion beam (FIB) method to measure the in-plane anisotropy of superconducting gap in more detail as well as the as-grown surfaces. It was found from the result that d[3,3]-Br was d -wave superconductor and the gap symmetry was d x 2 − y 2 as well as the previously studied ET salts. Therefore, d[3,3]-Br is also still weak in spite of stronger electron correlation than other ET salts. On the other hand, we also observed the two-type superconducting gaps which are the nodal and anti-nodal type gaps at the same angle surface. This suggests the coexistence of d x 2 − y 2 and dxy. It may be the evidence of the change from d x 2 − y 2 to dxy caused by the locally stronger electron correlation around the anti-ferromagnetic insulating region.

The kinetic energy of α′-(BEDT-TTF)2IBr2, α-(BEDT-TTF)2I3, and α-(BEDT-TTF)2NH4Hg(SCN)4 was estimated from the room-temperature optical conductivity measured from 50 to 30 000 cm−1. The kinetic energy of α′-(BEDT-TTF)2IBr2 was significantly smaller than that of α-(BEDT-TTF)2I3 that shows metal–insulator phase transition. A clear hysteresis was found in the magnetic susceptibility near the phase transition at around 30 K.

The low temperature phase in (EDT-TTF)2AuBr2 was investigated by 1H NMR and magnetic susceptibility measurements for protonated and partially deuterated single crystals. Two sharp peaks were observed in the temperature dependence of T 1 − 1 for both salts, associated with the SDW transition TSDW and the sub-phase transition T* common in the incommensurate SDW phase. The values of TSDW determined as 15 and 19 K for h- and d-salts, respectively, indicate the negative chemical pressure effect. The obtained ratios T*/TSDW 0.37 and 0.43 for h- and d-salts, respectively, are slightly larger than the common value T*/TSDW≅0.3 observed in (TMTCF)2X. The ratio T*/TSDW increases for larger TSDW and the low temperature sub-phase becomes more stable.

It is said that the quasi-two dimensional organic conductor ( BEDT-TTF ) 2 X forming two columns structure like α or θ salts, shows charge order (CO) state at low temperature. To confirm the existence of the CO state and the electron magnetism in α ′ phase whose symmetry is different from that of α and θ phases, we investigated 13 C-NMR on α ′ ‐ ( BEDT-TTF ) 2 IBr 2 , in which one-sided central carbon on BEDT-TTF molecules is substituted with 13 C. As a result, the change of spectrum was observed at 200 K which corresponds to CO transition and the angular dependence of spectrum at 15 K indicated that the charge ordering pattern was intra-column separating type. The spectrum in paramagnetic state can be examined by not only the difference of the charge density on on-site molecule but also the contribution from off-site molecules. This result suggested that the hyperfine coupling tensor changes after CO transition in which the charge separates extremely.

We measured the 13C-NMR spectrum and T 1 of κ -(BEDT-TTF) 2Cu(NCS)2 under pressure. Both of Knight shift and 1 / T 1 T showed the temperature independent behavior at low temperature under all pressures, therefore it is suggested that this material behaves as Fermi liquid at this region. Pressure dependence of Knight shift at low temperature cannot account the strong pressure dependence of the m c * , which observed by Shubnikov–de Haas (S–dH) measurement. On the other hand, pressure dependence of Korringa factor, calculated from Knight shift and 1 / T 1 T , is similar to that of the m c * . These results suggest that anti-ferromagnetic (AF) fluctuations contribute to the superconductivity in this material.

In recent years, concern has been raised about the charge fluctuation of the superconducting transition in the loosely dimerized molecular conductors. Not only the observation of the charge fluctuation is of considerably important but also the understanding of the mechanism of the fluctuation. We have observed degree of charge fluctuation of several β''-type ET salts. The β''-type ET salt is one of the best model compounds because the direction of the largest inter-site Coulomb interaction is perpendicular to that of the largest transfer integral. This structural property allows us to examine the role of inter-site Coulomb interaction from the viewpoint of the inter-molecular distance. The difference in the molecular charges between the charge rich site and the charge poor sites, Δρ, is correlated with the conducting behavior; the superconducting materials have the small but finite Δρ, whereas Δρ of the insulating (metallic) materials is large (almost zero). After the analysis of the configuration in the inter-molecular distances, we have found that the degree of fluctuation, Δρ, is attributed to the number of the most stable charge distribution(s), NS, and the number of the energy levels of the allowed charge distribution, NA. The superconducting materials belong to the condition of N ≥2 and N ge;2. Indeed, this condition contributes to the fluctuation of the molecular charges. © 2010 Elsevier B.V. All rights reserved.

The low-frequency dielectric constant was measured in the pressure induced incommensurate SDW phase of (TMTTF) 2 Br in order to investigate the dynamics of the SDW. Under the pressure above 0.5 GPa, the huge dielectric constant attributed to the motion of the SDW were observed. The temperature dependence of the real part of the dielectric constant ɛ ′ whose amplitudes grow with decreasing frequency shows the peak behavior in the incommensurate SDW phase. In contrast of the case of (TMTSF) 2 PF 6 , the peak temperature of ɛ ′ is constant, irrespective of the frequency. These peak temperature T P are scaled as T P / T SDW ∼ 0.3 irrespective of pressure for the pressure larger than 0.8 GPa and is associated with the sub-phase transition in the incommensurate SDW proposed by the NMR measurement. The dielectric properties are probably connected with the co-existence of the CDW component proposed for high temperature sub-phase.

We assessed 13C-NMR measurements in an organic salt, κ ‐ ( BEDT ‐ TTF ) 4 Hg 2.89 Br 8 , which exhibits superconductivity at 4.3 K under ambient pressure. We observed that ( T 1 T ) − 1 of H // and ⊥ layer at ambient pressure increased as the temperature was decreased to 7 K, but decreased further at lower temperatures, suggesting that the decrease of ( T 1 T ) − 1 was not due to the superconductive fluctuations, but due to the magnetism of the conduction electrons. Application of pressure suppresses ( T 1 T ) − 1 , with ( T 1 T ) − 1 becoming constant above 2 GPa. These results suggest that applying pressure alters the electron system from a non-Fermi liquid (NFL) to a Fermi liquid (FL) state and that antiferromagnetic fluctuations contribute to the origin of NFL behavior. Whereas most organic conductors show Fermi liquid behavior, this salt is an organic superconductor that shows NFL behavior due to the antiferromagnetic fluctuations.

The resistance and Hall resistance measurements have been carried out in the organic compound (TMTTF)2Br for various pressures. For the incommensurate SDW phase of (TMTTF)2Br stabilized above 0.5 GPa, the sign reversal of the Hall resistance was observed with decreasing temperature. In addition, a large hysteresis of the Hall resistance was observed above T*∼0.3TSDW, where TSDW is the SDW transition temperature. This behavior is possibly related to the sub-phase structure of incommensurate SDW phase, where the coexistence of the charge–density wave with the SDW was proposed for high temperature sub-phase. On the other hand, this type of hysteresis is not observed in the (TMTSF)2PF6 compound. These differences in both salts can be explained by taking into account the difference of the ratio of charge–density wave for high temperature sub-phase.

Zero-field μSR measurements on the antiferromagnetic Mott insulator β ′-(BEDT-TTF) 2 ICl 2 were performed in order to study the microscopic magnetic properties of this organics. The volume fraction of the antiferromagnetic phase was found to be temperature independent. Muon precession frequency, which is proportional to the magnitude of the magnetic moment at the dimer of two BEDT-TTF molecules, does not follow the simple model based on the mean-field approximation.

A π–d hybrid electronic system, (DMe-DCNQI)2Cu, where the π orbital of the organic molecule, DMe-DCNQI, is strongly hybridized with the dxy orbital of Cu, has been studied by 15 N and 13 C NMR at three sites. The analysis of Knight shift, K, and local spin susceptibilities in the π and d orbitals was carried out separately. The π and d spin susceptibilities were found to be quite different in magnitude and temperature dependence. Moreover, the Knight shift was separated into those of two constituent bands; a one-dimensional π band and a three-dimensional π–d band. The relative weight of the band susceptibilities is strongly temperature dependent.

The κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Br salts were synthesized from nondeuterated, partially, and fully deuterated BEDT-TTF molecules. The electrical resistance of these salts was examined systematically as functions of temperature and cooling rate, and found to change from metallic to insulating behaviors by the progressive deuterations and increasing the cooling rate. This means the active control of the correlation effect of electrons in this family.

The κ-(BEDT-TTF)2Cu[N(CN)2]Br is a quasi-two-dimensional superconductor with the highest Tc of ∼12 K among organic conductors. However, the antiferromagnetic insulating state appears by deuteration of BEDT-TTF (κ-d8-Br) or substitution of Cl (κ-Cl) for Br. The 13 C NMR measurements of these two insulating compounds, which are situated near the superconducting phase, were carried out to probe magnetic structure. The NMR spectra of κ-Cl and κ-d8-Br clearly indicate the commensurate antiferromagnetic structure with ordered moments of 0.45μB/(BEDT-TTF)2 and 0.3μB/(BEDT-TTF)2, respectively, which provides unambiguous evidence that κ-Cl and κ-d8-Br are Mott insulators.

The compound mentioned in the title is a quasi-two-dimensional organic conductor exhibits a metal–insulator transition accompanied by structural modification at T MI ∼190 K , while the tight-binding band calculation suggests a 3/4 filled band at higher temperatures. The 13 C NMR measurements have been performed on a single crystal to clarify the electronic nature of the metal–insulator transition. At room temperature, the 13 C NMR spectrum indicates that all BEDT-TTF molecules are electronically equivalent. Below TMI, however, it splits into two kinds of spectra with different Knight shifts and spin-lattice relaxation rates. These results show that charge disproportionation occurs below TMI and that long-range Coulomb interaction is important in this system.

Thermodynamic studies for a series of partially deuterated κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Br single crystals were performed in order to see variation of the normal-state density of sates around the two-dimensional Mott transition caused by the bandwidth control. The electronic specific heat coefficient γ was found to decrease monotonously when the system approaches the boundary from the metallic region. The Brinkman–Rice-type mass enhancement is absent near the critical boundary.