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We report the electron tunneling spectroscopy on partially deuterated κ-(BEDT-TTF-d[3,3])2Cu[N(CN)2]Br using a low temperature STM. In the superconducting state, tunneling spectra show the energy gap structure clearly; the conductance around the zero bias voltage is well reduced. V-shaped tunneling conductance curve inside the gap edge suggests the gap anisotropy. The linear dependence on the energy near zero bias is explained by the d-wave pairing with line nodes. By fitting to the d-wave gap model, we obtain the gap parameter as Δ=1.4–3.3 meV. Correspondingly, 2Δ/kTc is estimated as 2.7–6.4. The value is almost the same as that in κ-(BEDT-TTF)2Cu(NCS)2, d[0,0] and d[2,2] salts. The zero bias anomaly, which is an evidence for nodes of the superconducting gap, was found. The d-wave symmetry is strongly supported.

Raman and infrared-reflection spectra of κ -(BEDT-TTF) 2 Cu(N(CN) 2 )Br and its deuterated and partially deuterated analogues were measured at temperatures between 5 and 300 K and cooling rates from 1 to 20 K/min. It was found that, in partially deuterated samples, the interdimer electron–molecular vibration splitting of ν 3 mode in Raman spectra, and linewidths of some phonon peaks both in Raman and infrared spectra depend on the cooling rate. These observations were explained by disorder-related effects.

We measured the polarized Raman spectra of θ-(BEDT-TTF) 2 RbZn(SCN) 4 (RbZn) and (BEDT-TTF) 3 CuBr 4 (CuBr) to investigate the detailed property of charge ordering (CO), and discussed an approach for analyzing the vibrational spectra of CO systems. The Raman spectra of the two compounds showed multiple peaks around the CC stretching region. With the help of isotope-shift measurements, the multiple peaks of RbZn were assigned to two symmetric CC stretching modes, called ν 2 and ν 3 . We used the vibronic signals of ν 3 to characterize the spatial symmetry of charge distribution, and employed the peak frequencies of ν 2 with weaker vibronic coupling effect to the estimation of charge disproportionation ratio. Similar spectral analysis was applied to CuBr salt to verify whether the approach can be applied to other systems.

The IR and Raman spectra of β″-(ET)3X2 [X = HSO4 and ClO4] salts were measured at various temperatures below 300 K. The ν2 and ν27 modes exhibit the splitting into two peaks below the metal–insulator transition temperature. This phenomenon is ascribed to the charge ordered (CO) state. The CO patterns of the presented compounds were determined on the basis of the numerical calculation of the vibronic ν3L mode. The assignment of the ν27 mode of ET+ was confirmed through the measurement of the reflectance spectra of the 1:1 salts (ET)ClO4, (ET)AuCl2Br2 and the isotope analogues. The ν27 mode is the efficient probe to the site charges of the ET salts.

Synthesis of deuterated and 13 C -enriched BEDT-TTF, and the results of 13 C NMR (nuclear magnetic resonance) measurement of κ-(BEDT-TTF)2Cu[N(CN)2]Br salt are reported where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene. We synthesized the BEDT-TTF molecule 13 C -enriched on only one side of the central carbon sites. By using this molecule, we could avoid the Pake doublet and estimate the density of states from the Knight-shift and the spin–lattice relaxation rate. The reduced mass effect predicted from the specific heat measurement was not observed in the 13 C NMR measurement.

We reported design and synthesis of new peri-condensed heterocycles which do not contain TTF type conjugated systems, that is, three isomers of dithiaperylenes (DTPR), one isomer of dithiapyrene (DTPY) and their methylthio or methylseleno derivatives. These donors showed two-stage redox behavior whose potentials are comparable to that of TTF. Good correlation was obtained between the oxidation potentials and the HOMO energies calculated by the PM3 method. A number of CT complexes prepared were classified into three groups, neutral, ionic, and non-V-shape groups. Among them, the non-V-shape group complexes contained highly conducting complexes including molecular metals. Most of the CT salts with inorganic anions having high conductivities showed lower electronic transition energies than 0.5 eV.

Using partially deuterized BEDT-TTF molecules, we performed 13 C-NMR study of a series of partially deuterized K-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br salts, where BEDT-TTF is bis-(ethylenedithio)tetrathiafulvalene. We synthesized partially deuterized BEDT-TTF molecules 13 C-enriched on only one side of the central carbon sites. The substitution of one side of the central carbon avoid the Pake doublet and we can estimate the density of states from the Knight-shift and the spin-lattice relaxation rate. The reduced mass effect predicted from the specific heat measurement near the SC-AF1 boundary was not observed in the 13 C- NMR measurement but the phase separation behavior was observed.

The title compound undergoes a neutral-ionic (N-I) phase transition under pressure. In order to examine the electronic state of BEDT-TTF and Cl,MeTCNQ molecules separately by NMR, we prepared the complex with Cl,MeTCNQ and C, deuterium-substituted BEDT-TTF molecules. The 13 C and 1 H NMR measurements were performed at ambient and applied pressures. Under 8 kbar, the N-I transition was found to be continuous. We also found that the I-phase is nonmagnetic state.

In κ-(BEDT-TTF) 2 X, the relationship between the AF-fluctuation and the superconductivity has been discussed by many researchers. In order to investigate the mechanism of the superconductivity in κ-(BEDT-TTF) 2 X, we prepared the alloy of K-(BEDT-TTF) 2(1-X) (BEDSe-TTF) 2X Cu[N(CN) 2 ]Br and measured the magnetic properties of the alloy. The increase of X shifted T c lower and the superconductivity was suppressed over X=0.33. To check the magnetic fluctuation, we also measured the spin-lattice relaxation rate (T 1 T) -1 of the series of the alloy system.

Raman studies of α-(BEDT-TTF) 2 I 3 [BEDT-TTF is bis-ethylenedithiolo(tetrathiafulvalene)] have been performed to investigate the charge distribution between BEDT-TTFs below and above the metal-insulator phase transition at T M-1 =135 K. Following the crystal-symmetry lowering at T M-1 , clear ±0.3e deviation from average 0.5e charge has been found in the nonmagnetic insulating phase. In the paramagnetic semi-metal-like phase, the split of one of the Raman active mode suggests charge nonequivalence between donors.

κ-(BEDT-TTF) 2 X system is well known as the strong correlated electron system with the phase boundary of the superconducting and the antiferromagnetic ordering phases. We controlled the boundary with the partial deuterization technique on κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br and found the boundary was sensitive to cooling rate around at 80 K, at which the lattice anomaly occurred. We also found the external magnetic field dependence of the boundary.

A single crystal of α′-(BEDT-TTF) 2 IAuBr was synthesized and the crystal structure was determined by X-ray analysis. The structure was found to be isostructural to α′-(BEDT-TTF) 2 AuBr 2 , having the characteristics of α′-type salts in that the donor molecules are stacked to form a dimerized chain. The electronic structure of α′-type salts was proved to be one-dimensional along the stacking direction from the analysis of the polarized reflectance spectra obtained by use of the microspectroscopic technique.

The radical salts of NiPc, PtPc, and NiTBP were prepared by the method of electrochemical oxidation. The radical salts of NiPc and PtPc have 2:1 chemical composition and are metallic, the crystal structure being composed of tetragonally packed molecular columns with the metal-over-metal stacking mode. On the other hand, the radical salts of NiTBP with tetrahedral and octahedral counter anions have 3:2 chemical composition and are semiconductive, the crystal structure being composed of hexagonally packed molecular columns including a periodic unit of NiTBP trimer. All these materials have predominantly oxidized macrocycles, a small on-site Coulomb energy, and a small electron-phonon interaction.

Highly conducting materials of (phthalocyanato)nickel hexafluoroarsenate, (NiPc) 2 AsF 6 , and hexafluoroantimonate, (NiPc) 2 SbF 6 , were prepared by the use of an electrochemical technique. The crystal structures resemble that of NiPc(I 3 ) 0.33 , which is composed of NiPc molecular columns encompassed by triiode anions. The electrical conductivity of these salts exhibits a metallic behavior at least down to 200 K. It was concluded from the ESR experiment that (NiPc) 2 SbF 6 is a doubly mixed valence compound.

A single crystal of s″-(BEDT-TTF) 2 ICl 2 was synthesized electrochemically, and the crystal structure was determined by X-ray analysis. This s″-type crystal was characterized by means of the electrical resistivity, electron spin resonance, X-ray diffraction, and polarized reflectance spectrum. The temperature dependence of the electrical resistivity which was proportional to T down to 10 K shows a typical metallic behavior. The ESR spectrum exhibited a Dysonian line-shape. The intensity of the spin susceptibility abruptly decreased at 17 K, although the electrical resistivity and the Bragg diffraction intensity showed no discontinuous change: this indicates the occurrence of a magnetic phase transition. The reflectance spectrum for the //c polarization showed a Drude-like dispersion already at room temperature. The anisotropic two-dimensional electronic structure was examined by the reflectance spectrum analysis.

Semiconductive (BEDT-TTF) 2 (IBr 2 ) 2 (TCE) 0.5 salt, which is isostructural to e-I 3 , changes to metallic ones with the loss of their weight when tempered under reduced pressure. The metallic behavior retains down to 0.5 K.

3,10-Dithiaperylene (DTPR, 1a ), 1,6-dithiapyrene (DTPY, 2a ), and their dephenyl derivatives, Ph2DTPR ( 1b ) and Ph2DTPY ( 2b ), and ethylenedithiolo derivative (ETDTPY, 3 ) were prepared as examples of molecular design for condensed type donors with two sulfur atoms. They are termed peri-condensed Weitz-type donors. The electrochemistry indicates that these heterocycles are actually two-stage redox systems with low oxidation potentials, indicating large enhancement of the donor ability. We obtained relatively high conductive CT complexes utilizing these donors and TCNQ-type acceptors. Interestingly, Ph2DTPR-DDQ0.75 shows the high conductivity (compressed pellet, δ = 0.5 Scm−1) despite the fact that the complex consists of neither TTF-type donor nor TCNQ-type acceptor. In addition, ETDTPY gave highly conducting iodine complex (single crystal, 42 Scm−1). The crystal structures of Ph2DTPR, Ph2DTPR-ClO4, DTPY, and (Ph2DTPY)2I3 show columnar stacks of donor molecules.

(BEDT-TTF)2Cu(NCS)2 was found to be the first ambient pressure organic superconductor with the Tc higher than 10 K. The salt has a layered structure which is composed of donor and anion sheets. The packing pattern of donors of the Cu(NCS)2 salt is nearly analogous to κ-(BEDT-TTF)2I3. In anion layers CuI is trigonal coordinated to two N atoms and one S atom to construct a one-dimensional planar polymer. The valence state of CuI was observed by ESCA at 298 K and ESR at 298-4 K. One broad Lorentzian ESR signal ascribed to a BEDT-TTF cation radical was obtained. The g-values are independent of temperature, while the linewidth shows broadening with lowering temperature even though the resistivity decreases below 90 K. The ESR magnetic susceptibility is constant down to 90 K, which is suggesting Pauli-like paramagnetism. The thermopower is anisotropic in the two-dimensional bc plane, which is originated from the anisotropy of the band structure.