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A family of organic conductors, α-(BEDT-TTF)2MHg(SCN)4, is known to show the density wave (DW) state for M = Tl, K, and Rb salts, or the superconducting (SC) state for M = NH4 salt at low temperatu...

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.

This study presents a topology optimization method to reduce cogging torque, applied to the design of the stator core of an interior permanent magnet motor. The proposed method uses a reaction-diffusion equation and optimization is separately performed based on two objective functions: 1) minimization of the cogging torque itself, for a number of rotor positions; and 2) minimization of the magnetic energy variation. The optimization results show that configurations having dummy slots are desirable, but the number of dummy slots differs according to the objective function used.

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 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 charge-ordered state in a quasi-two-dimensional organic superconductor β''−(BEDT-TTF)4[(H3O)Ga(C2O4)3]⋅C6H5NO2 has been investigated using C13 NMR spectroscopy in a high magnetic field. Enhanced resolution of the high-field spectrum allows us to estimate the site charges in the low-temperature charge-ordered state below 8.5 K. The observed strong increase in the charge imbalance suggests that superconductivity appears on the electronic state with a strong charge modulation. From the NMR intensity ratio of signals from the charge-rich and charge-poor sites, we discuss a possible charge pattern with threefold modulation, which could be stabilized by the effects of electron-electron correlations.

Unconventional superconductivity has been frequently found after the suppression of the order in the spin degrees of freedom. Properties of unconventional superconductivity near magnetic order have been intensively studied since the discovery of heavy fermion and cuprate superconductors. In these systems, superconductivity is induced by magnetic critical fluctuations enhanced near the second-order phase transition. The organic superconductors (TMTSF)2X (TMTSF: tetramethyltetraselenafulvalene) and κ-(BEDTTTF)2X (BEDT-TTF: bisethylenedithio-tetrathiafulvalene) are also categorized by magnetic-fluctuation-induced superconductivity [1,2]. In some BEDT-TTF salts, however, superconductivity was found near the order in the charge degrees of freedom. One of the most intensively studied examples is the α-(BEDT-TTF)2X family, in which superconductivity appears after suppressing charge instability by chemical substitution or application of mechanical pressures [3‐6]. Theoretical studies have suggested that superconducting (SC) pairs can be mediated by critical charge fluctuations near the charge ordering (CO), which is caused by a sizable off-site Coulomb repulsion [7]. The properties of superconductivity near charge instability should be investigated to understand the diversity of SC pairing mechanisms. To reveal the relationship between superconductivity and charge instability, a phase diagram for various α-type BEDTTTF salts has been proposed [5]. In this phase diagram, the ratio of lattice parameters c/a was used as the tuning parameter, which modifies the anisotropy of the transfer integrals in the conduction (ac � ) plane. Among the α-(BEDTTTF)2X salts, a clear CO transition at TCO = 135 K was reported in α-(BEDT-TTF)2I3 (I3 salt) with c/a � 0.85 [8]. The uniaxial strain along the c direction decreases the c/a ratio to induce superconductivity with the transition temperature Tc reaching 7 K [4]. The resistivity in c axial strainshowssemiconductingbehaviorbeforetheSCtransition, while a axial strain induces metallic resistivity down to the lowest temperature without a SC transition. In another α-type salt, α-(BEDT-TTF)2NH4Hg(SCN)4 (NH4 salt) with a

We performed $^{13}\mathrm{C}$-NMR experiment and measured spin-lattice relaxation rate divided by temperature $1/{T}_{1}T$ near the superconducting (SC) transition temperature ${T}_{c}$ in $\ensuremath{\kappa}$-(BEDT-TTF)${}_{2}$Cu[N(CN)${}_{2}$]Br ($\ensuremath{\kappa}$-Br salt), and $\ensuremath{\kappa}$-(BEDT-TTF)${}_{2}$Cu(NCS)${}_{2}$ ($\ensuremath{\kappa}$-NCS salt). We observed the reduction of $1/{T}_{1}T$ starting at the temperature higher than ${T}_{c}$ in $\ensuremath{\kappa}$-Br salt. Microscopic observation of the quasiparticle density of states in the fluctuating SC state revealed the effects of short-range Cooper pairs induced in the normal state to the quasiparticle density of states. We also performed systematic measurements in the fields both parallel and perpendicular to the conduction plane in $\ensuremath{\kappa}$-Br and $\ensuremath{\kappa}$-NCS salts, and confirmed that the reduction of $1/{T}_{1}T$ above ${T}_{c}$ is observed only in $\ensuremath{\kappa}$-Br salt regardless of the external field orientation.

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.

We review the challenges for atomic scale modeling of alternative gate dielectric stacks. We begin by highlighting recent achievements of state-of-the-art atomistic simulations of the Si-SiO/sub 2/ system, showing how such calculations have elucidated the microscopic origins of several important experimental phenomena. For the benefit of readers who may be unfamiliar with the simulation tools, we overview and compare the relevant methods. We then describe the difficulties encountered in extending these approaches to investigate high-k dielectric stacks, pointing out exciting research directions aimed at overcoming these challenges. We conclude by presenting a roadmap of computational goals for atomic scale modeling of alternative gate dielectrics.

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.

The pressure dependence of the optical reflectivity spectrum [ R ( ω ) ] of deuterated κ - ( BEDT - TTF ) 2 Cu [ N ( CN ) 2 ] Br ( d 44 ) at T = 4.5 K was determined. At the ambient pressure, d 44 under fast cooling conditions forms an antiferromagnetic insulator (AFI) phase, as confirmed by the wavenumber of the ν 3 ( a g ) vibration mode. At the pressures in the range of several MPa, the optical spectrum changes to that of a metal that matches a non-deuterated material consisting of AFI and PM (paramagnetic metallic) spectra. This indicates that the phase separation between the AFI and PM phases appears at intermediate pressures. The phase size of the separated phase is smaller than the instrumental spatial resolution of 50 μ m , based on the inability of our methods to record it.

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.

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.

Quasi-one-dimensional organic conductors (TMT$C$F)${}_{2}$$X$ have various electric and magnetic properties. Although theoretical and experimental studies have suggested that (TMTTF)${}_{2}$Br has the properties of commensurate antiferromagnetism, details of the magnetic structure of this compound are unclear. Two types of antiferromagnetism are expected, one due to a localized electron and the other to the nesting of the Fermi surface. We therefore assessed the antiferromagnetic structure of (TMTTF)${}_{2}$Br using ${}^{13}$C NMR. Site assignment of the observed antiferromagnetic spectrum confirmed that there were two magnetic molecular sites, with staggered moments and amplitude of 0.11${\ensuremath{\mu}}_{B}$/molecule, as well as nonmagnetic molecular sites. A commensurate structure with antiferromagnetic ordering of ($\ensuremath{\uparrow}\ensuremath{\circ}\ensuremath{\downarrow}\ensuremath{\circ}$) along a one-dimensional chain would be expected as the freezing of antiferromagnetic fluctuations in the charge-ordered phase of the (TMTTF)${}_{2}$AsF${}_{6}$ salt. The presence of a nodal site is strongly suggestive of the nesting type antiferromagnetism. The fine structure of the antiferromagnetic spectrum suggests superlattice along the interchain direction. We could not observe line broadening due to the charge order above the antiferromagnetic transition.

To explore the connection between $\ensuremath{\alpha}$-(BEDT$\ensuremath{-}$TTF)${}_{2}$I${}_{3}$ and $\ensuremath{\alpha}$-(BEDT$\ensuremath{-}$TTF)${}_{2}$$M$Hg(SCN)${}_{4}$ ($M=\text{K}$, Rb, Tl and NH${}_{4}$) and to resolve the difference between band picture and charge fluctuation of $\ensuremath{\alpha}$-(BEDT$\ensuremath{-}$TTF)${}_{2}$$M$Hg(SCN)${}_{4}$, we utilized ${}^{13}$C-NMR to examine $\ensuremath{\alpha}$-(BEDT$\ensuremath{-}$TTF)${}_{2}$RbHg(SCN)${}_{4}$ under the conditions with a large hyperfine coupling constant at each site. The temperature dependence of site susceptibility showed the development of spin disproportionation as observed in $\ensuremath{\alpha}$-(BEDT$\ensuremath{-}$TTF)${}_{2}$I${}_{3}$. We found that the linewidth of the A site only increased as temperature decreased from 200 to 100 K, a change associated with the development of lattice modulation. These findings indicate that density-wave modulation occurs during charge disproportionation instability.

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.

In the temperature-pressure phase diagram of the organic superconductor (TMTSF)${}_{2}$PF${}_{6}$ (TMTSF: tetramethyltetraselenafulvalene), the superconducting phase and the spin-density-wave (SDW) phase are adjacent to each other. This salt exhibits non-Fermi-liquid (NFL) behavior and superconductivity under pressure. Its superconductive property does not exist at higher pressures where Fermi-liquid (FL) behavior is exhibited. In order to investigate the origin of NFL behavior, systematic $^{13}\mathrm{C}$-NMR measurement of this salt has been assessed under pressure in a wide temperature range. At low temperatures, $({T}_{1}T){}^{\ensuremath{-}1}$ increases, and this increase is suppressed by the increasing pressure. These results suggest that applying pressure alters the electron system from the NFL to the FL state, and that antiferromagnetic fluctuations contribute to the origin of NFL behavior. The connection between the emergence of FL behavior and the disappearance of superconductivity suggests that the SDW fluctuation relates to the mechanism of the superconductivity in (TMTSF)${}_{2}$PF${}_{6}$.

${\ensuremath{\beta}}^{\ensuremath{'}\ensuremath{'}}$-(BEDT$\ensuremath{-}$TTF)${}_{3}$Cl${}_{2}$$\ifmmode\cdot\else\textperiodcentered\fi{}$2H${}_{2}$O [BEDT$\ensuremath{-}$TTF: $\underline{\mathrm{b}}$is-($\underline{\mathrm{e}}$thylene$\underline{\mathrm{d}}$i$\underline{\mathrm{t}}$hio)$\underline{\mathrm{t}}$etra$\underline{\mathrm{t}}$hia$\underline{\mathrm{f}}$ulvalene] is superconductive under pressures, whereas the salt exhibits metal-insulator (MI) transition under ambient pressure. The insulator phase in the salt was examined using the charge density wave (CDW) phase that was obtained from band calculation. The charge-ordered (CO) state was recently proposed as the insulator phase of the salt, and the mechanism of superconductivity intermediated by charge fluctuation was suggested. We accessed ${}^{13}$C-NMR on ${\ensuremath{\beta}}^{\ensuremath{'}\ensuremath{'}}$-(BEDT$\ensuremath{-}$TTF)${}_{3}$Cl${}_{2}$$\ifmmode\cdot\else\textperiodcentered\fi{}$2H${}_{2}$O at ambient pressure and under pressure up to 1.6 GPa. At ambient pressure, the NMR spectrum changed at approximately 100 K. Three isolated peaks appeared at low temperatures, suggesting that the CO state exists below 100 K, and spin-gap behavior was observed. By analyzing the chemical shift, the charges on the three sites were estimated as $\ensuremath{\sim}$+0.4$e$, $\ensuremath{\sim}$+0.6$e$, and $\ensuremath{\sim}$+1.0$e$. The ratio of peak intensity and unsymmetrical peak position suggest the CO state with some symmetry breaking. When pressure is applied, the splitting of the NMR peaks in the CO state is reduced. The salt finally exhibits superconductivity at 1.6 GPa, spin-gap behavior observed at ${({T}_{1}T)}^{\ensuremath{-}1}$ below 1.3 GPa suddenly disappears, whereas the NMR spectrum predicts that charge disproportionation coexists with superconductivity. The suppression of the spin-singlet formation observed in ${({T}_{1}T)}^{\ensuremath{-}1}$ at 1.6 GPa suggests the metallic state with the charge disproportionation and the CO instability with some symmetry breaking.

$\ensuremath{\kappa}$-(BEDT-TTF)${}_{2}$Cu(NCS)${}_{2}$ [BEDT-TTF: bis-(ethylenedithio)-tetrathiafulvalene] behaves as a semiconductor at high temperatures, whereas it behaves as a Fermi liquid just above the superconducting transition temperature. To reveal the cause of this behavior, we experimented on $\ensuremath{\kappa}$-(BEDT-TTF)${}_{2}$Cu(NCS)${}_{2}$, in which one side of the central C$=$C in the BEDT-TTF molecules is substituted with $^{13}\mathrm{C}$ nuclei. We perfomed $^{13}\mathrm{C}$-nuclear magnetic resonance (NMR) spectroscopy on this salt and measured the temperature dependence of its spectral linewidths and its spin-spin relaxation time $T$${}_{2}$. We found anomalies in its linewidths and $T$${}_{2}$, which we connected to the ethylene motion within the salt. Compared with the $^{13}\mathrm{C}$-NMR measurements of $\ensuremath{\kappa}$-(BEDT-TTF-$d$8)${}_{2}$Cu(NCS)${}_{2}$, we obtained the experimental evidence of the connection between the ethylene motion and the conduction electrons. Considering this connection, we examined the semiconductive behavior of $\ensuremath{\kappa}$-(BEDT-TTF)${}_{2}$Cu(NCS)${}_{2}$ at high temperatures. The contribution of ethylene motion to the electronic state is thought to be a common feature of BEDT-TTF salts.

First principles calculations aimed at quantifying the effects of zirconium and hafnium incorporation at a model silicon/silicate interface have been performed. The tetrahedral bonding character of silicates allows useful comparisons as well as important new distinctions to be drawn with the familiar Si/SiO/sub 2/ system. The calculated energy cost of forming (Zr,Hf)-Si bonds suggests that SiO/sub 2/-like bonding is energetically favored over silicide-like bonding at the Si interface. The calculations also suggest that the volume strain associated with Zr or Hf incorporation may lead to increased stress, both in the bulk oxide and in the interfacial transition region.

An organic salt, $\ensuremath{\kappa}\text{\ensuremath{-}}{(\text{BEDT-TTF})}_{4}{\text{Hg}}_{2.89}{\text{Br}}_{8}$ exhibits superconductivity at 4.3 K under ambient pressure suggesting non-Fermi-liquid (NFL) behavior just above ${T}_{c}$. Whereas most organic superconductors are controlled by the bandwidth in the half-filled electron system, this salt realizes a carrier doping away from the half-filled electron system as well as high-${T}_{c}$ cuprates. In order to investigate the origin of NFL behavior, we assessed $^{13}\text{C}$-NMR measurements in this salt and observed the antiferromagnetic fluctuation as same as in an organic antiferromagnet $\ensuremath{\kappa}\text{\ensuremath{-}}{(\text{BEDT-TTF})}_{2}\text{Cu}[\text{N}{(\text{CN})}_{2}]\text{Cl}$ with the gap structure. Application of pressure suppresses ${({T}_{1}T)}^{\ensuremath{-}1}$ and shifts its maximum to lower temperatures with ${({T}_{1}T)}^{\ensuremath{-}1}$ becoming constant above 2 GPa. These results suggest that applying pressure alters the electron system from NFL to FL state and that antiferromagnetic fluctuations contribute to the origin of NFL behavior.

The charge order (CO) state can be observed by microprobe measurements such as nuclear magnetic resonance (NMR) and infrared spectroscopy. We used the infrared spectroscopy to examine ${(\text{TMTTF})}_{2}{\text{AsF}}_{6}$ and confirmed the CO transition seen in previous $^{13}\text{C}$-NMR studies. However we found the degree of charge disproportionation, $\ensuremath{\Delta}\ensuremath{\rho}=0.16$, to be smaller than that obtained from the analysis of ${T}_{1}$ in $^{13}\text{C}$-NMR and the redistribution of charge density below spin Peierls transition predicted by $^{13}\text{C}$-NMR was not observed at low temperature. We estimated the degree of spin disproportionation to be 0.11 from the analysis of the NMR shift in previous NMR studies. This small disproportionation does not require the redistribution of charge density at low temperature. The different behaviors of ${T}_{1}$ at charge-rich and charge-poor molecular sites observed by $^{13}\text{C}$-NMR can be examined by the contribution of the commensurate antiferromagnetic fluctuation with $4{k}_{F}$.

We assessed carbon-13 nuclear magnetic resonance ($^{13}\text{C}$ NMR) measurements of the layered organic salt ${\ensuremath{\beta}}^{\ensuremath{'}}\text{\ensuremath{-}}{(\text{BEDT-TTF})}_{2}{\text{ICl}}_{2}$, which exhibits antiferromagnetic transition at ambient pressure and 22 K and superconductive transition at 8.2 GPa and 14.2 K (the highest known superconductive transition temperature among organic superconductors). By analyzing the $^{13}\text{C}$ NMR spectrum with the tensor, we determined the antiferromagnetic moment of this salt to be ${\ensuremath{\mu}}_{B}$ per dimer at ambient pressure, strongly indicating that this salt is a dimer Mott insulator. From NMR measurements under pressure, we found that the structure of the antiferromagnetic phase changed at 0.6 GPa. The moment of this antiferromagnetic phase was estimated to be $0.47{\ensuremath{\mu}}_{B}$ per dimer at 0.6 GPa and 26 K. In addition, applying pressure rapidly decreased the spin susceptibility in the paramagnetic state, and the pressure dependence of ${T}_{N}$ showed anomalous behavior consistent with theoretical proposals, including dimensional crossover.

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.

Among quasi-two-dimensional organic conductors, ${(\text{BEDT-TTF})}_{2}X$, what form the two column structure of $\ensuremath{\alpha}$ or $\ensuremath{\theta}$ is thought to show a charge-ordering insulating state. The ${\ensuremath{\alpha}}^{\ensuremath{'}}$ modification is the other candidate for a charge-ordering state. To determine the existence of a charge-ordering state and electron magnetism in the ${\ensuremath{\alpha}}^{\ensuremath{'}}$ phase, which has a symmetry that differs from that of the $\ensuremath{\alpha}$ and $\ensuremath{\theta}$ phases, we utilized $^{13}\text{C}\text{-NMR}$ to examine ${\ensuremath{\alpha}}^{\ensuremath{'}}\text{\ensuremath{-}}{(\text{BEDT-TTF})}_{2}{\text{IBr}}_{2}$ in which one side of the central carbon on the BEDT-TTF molecule is substituted with $^{13}\text{C}$ nuclei. We observed changes in its spectrum at 200 K. The angular dependence of the NMR shift at 15 K indicated that the charge-ordering pattern is intracolumn disproportionation and the ratio of charge disproportionation on the spin-poor site and spin-rich sites is almost 1:0. The angle dependence of NMR spectrum at 60 K suggests that the hyperfine coupling tensor in the paramagnetic charge-ordering state is determined not only by the charge density of on-site molecules but also by the contribution of off-site molecules. The change in hyperfine coupling tensor must be taken into account in NMR studies of the paramagnetic CO state.

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.

We have examined time-averaged charges of the molecular donors around the phase boundary between the insulating, superconducting, and metal phases for ${\ensuremath{\beta}}^{\ensuremath{''}}$-type ET [$\mathrm{ET}=\text{bis}$-ethelenedithio-tetrathiafulvalene] salts with one (two) hole(s) per two (three) molecules by using vibrational spectroscopy. Around the phase boundary, the site charges are neither those expected for a well-developed charge-ordered (CO) state nor a homogeneous distribution. The molecular charges exhibit an inhomogeneous distribution just above the insulator-superconductor transition temperature. We have analyzed the distribution of the site charges from the viewpoint of the alternation of intersite Coulomb interactions along the stacking direction. The closeness in the energy of several CO patterns mostly contributes to the inhomogeneous distribution, whereas a large difference (no difference) in the energy levels contributes to the CO (homogeneous) state. Our observations indicate that the instability due to the closeness in the energy of several distributions correlates with the insulator-superconductor transition in nondimerized or weakly dimerized molecular conductors.

The magnetic field-induced superconductor-insulator-metal transition (SIMT) in partially deuterated $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br, which is just on the Mott boundary, has been observed using the infrared magneto-optical imaging spectroscopy. The infrared reflectivity image on the sample surface revealed that the metallic (or superconducting) and insulating phases coexist and they have different magnetic field dependences. One of the magnetic field dependence is SIMT that appeared on part of the sample surface. The SIMT was concluded to originate from the balance of the inhomogenity in the sample itself and the disorder of the ethylene end groups resulting from fast cooling., Comment: 5 pages, 5 figures, to appear in Phys. Rev. B

In order to investigate the nature of the insulator phase of $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{Cu}}_{2}{(\mathrm{C}\mathrm{N})}_{3}$ [where BEDT-TTF represents bis(ethylenedithio)terathiofulvalene] and why this salt is a superconductor under pressure but not under ambient pressure, we examined the $^{13}\mathrm{C}$ NMR spectra and spin lattice relaxation rate of $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{Cu}}_{2}{(\mathrm{C}\mathrm{N})}_{3}$ under pressure. The spin susceptibility evaluated from the Knight shift decreased with increase in pressure, and line broadening was suppressed above a critical pressure. The temperature dependence of ${({T}_{1}T)}^{\ensuremath{-}1}$ for $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{Cu}}_{2}{(\mathrm{C}\mathrm{N})}_{3}$ above a critical pressure was that for $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}X$, where $X$ was $\mathrm{Cu}[\mathrm{N}{(\mathrm{C}\mathrm{N})}_{2}]\mathrm{Br}$ or $\mathrm{Cu}{(\mathrm{N}\mathrm{C}\mathrm{S})}_{2}$. These results suggest that the electronic structure of $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{Cu}}_{2}{(\mathrm{C}\mathrm{N})}_{3}$ under pressure is similar to that of other $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}X$ salts. The results support our model that electron inhomogeneity and hopping conduction, which are common features of semiconductivity in $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}X$ at high temperatures, are responsible for the insulator phase in $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{Cu}}_{2}{(\mathrm{C}\mathrm{N})}_{3}$. The electron inhomogeneity suppresses the semiconductor-metal transformation and superconductivity observed in other $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}X$ salts.

We present the temperature-dependent infrared and Raman spectra of ${\ensuremath{\beta}}^{\ensuremath{''}}\text{\ensuremath{-}}{(\mathrm{ET})}_{3}{X}_{2}$ ($X=\mathrm{H}\mathrm{S}{\mathrm{O}}_{4}$ and $\mathrm{Cl}{\mathrm{O}}_{4}$; $\mathrm{ET}=\mathrm{bis}$-ethylenedithio-tetrathiafulvalene) compounds which undergo a metal-insulator transition. The infrared-active ${v}_{27}$ mode discontinuously split into two bands at the metal-insulator transition temperature of $127\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in the $X=\mathrm{H}\mathrm{S}{\mathrm{O}}_{4}$ salt, whereas, the corresponding mode continuously changed across the metal-insulator transition temperature of $\ensuremath{\sim}170\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in the $X=\mathrm{Cl}{\mathrm{O}}_{4}$ salt. In both compounds, the charge-sensitive ${v}_{27}$ mode split into two in the insulating phase. This drastic spectral change indicates that the metal-insulator transition originated in the charge ordering. Employing the frequencies of the split ${v}_{27}$ bands, the site charges are estimated to be $+{0.3}_{4}$ and $+{0.8}_{1}$ for $X=\mathrm{H}\mathrm{S}{\mathrm{O}}_{4}$ and $+{0.3}_{6}$ and $+{0.8}_{1}$ for $X=\mathrm{Cl}{\mathrm{O}}_{4}$. We also estimated the site charges using the Raman-active ${v}_{2}$ mode and obtained consistent results. Examining the selection rule of the ${v}_{3}$ mode, we reached the conclusion that the unit cell with space group $P1$ has a pseudoinversion center in the charge-ordered phase. Based on the symmetry, we propose a charge-ordering pattern for the $X=\mathrm{H}\mathrm{S}{\mathrm{O}}_{4}$ and $X=\mathrm{Cl}{\mathrm{O}}_{4}$ salts, which is quite different from that of the $X=\mathrm{Re}{\mathrm{O}}_{4}$ salt reported previously. We qualitatively discuss the differences in the charge-ordering pattern considering the anisotropic intersite Coulomb interaction.

A $^{13}\mathrm{C}$-NMR study on nondeuterated and partially deuterated $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{C}\mathrm{N})}_{2}]\mathrm{Br}$ is reported, where BEDT-TTF is bis(ethylenedithio)tetra-thiafulvalene. By using a BEDT-TTF molecule with $^{13}\mathrm{C}$ as one of its central carbons, we could estimate the density of states from the Knight shift and the spin-lattice relaxation rate. Although the reduced mass effect predicted from the specific-heat measurement was not observed in the $^{13}\mathrm{C}$-NMR spectrum, a metal-to-antiferromagnetic phase transition was observed with a phase separation at around $18\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ on the half-deuterated $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{C}\mathrm{N})}_{2}]\mathrm{Br}$ under a high magnetic field. No such transition occurred in the half-deuterated salt under a zero or low field. These results point to a first-order field-induced metal-insulator transition. These findings can explain the complex phenomena observed near the phase boundary under a high magnetic field.

$\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}X$ salts exhibit a wide range of properties from superconductivity to magnetic ordering. The phase diagram of this system has been understood as the competition between anti-ferromagnetic insulating behavior and superconductivity. The $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}X$ system has been well explained using a parameter, U/W, as well as the high ${T}_{c}$ cuprates. $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{Cu}}_{2}{(\mathrm{CN})}_{3}$, however, behaved as an insulator without magnetic ordering. This salt cannot be described by the phase diagram described by the competition between superconductivity and magnetism. It is interesting to explore the nature of this insulating phase with an eye toward understanding the universal phase diagram of the $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}X$ system. Magnetic frustration due to the triangular spin lattice has recently been reported for $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{Cu}}_{2}{(\mathrm{CN})}_{3}$ from $^{1}\mathrm{H}$-nuclear magnetic resonance (NMR) study. To investigate the insulating properties of this salt, we characterized it using $^{13}\mathrm{C}\text{\ensuremath{-}}\mathrm{NMR}$. In contrast to previous $^{1}\mathrm{H}\text{\ensuremath{-}}\mathrm{NMR}$ studies, at low temperatures, we observed line broadenings that were proportional to the hyperfine coupling constants, which suggested inhomogeous electron localization. We also observed antiferromagnetic fluctuations which, as is the case with other salts, intensified with decreasing temperature. To understand the electronic properties of $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}X$ system, in addition to the U/W, the electron localization effect from the relatively narrow bandwidth is important.

A partially deuterated κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Br salt, which is a superconductor situated near the Mott insulator, has been investigated by resistivity measurements under magnetic fields. The superconducting transition of this salt is replaced by the first-order metal–insulator transition by magnetic field. This field-induced transition fades away when the sample cooling around 80 K is slowed down. The present findings lead us to bring to mind possible realization of the ideal electric switch controllable with the magnetic field.

The phase diagram of κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br around the metal–insulator (MI) boundary controlled by partially deuteration and by cooling rate through the 80 K anomaly has been investigated by resistivity measurements under magnetic fields. The humps of resistance were observed at 33.5 K corresponding to the T * anomaly and at 9.5 K with the hysteresis of resistance in the partially deuterated sample for slowly cooled. According to approach to the critical region of MI transition from the metallic side by the increase of cooling rate: (a) the hump of resistance at the T * anomaly is shifted towards a lower temperature and (b) the temperature of the resistance hump with the hysteresis increases. Our results suggest that these anomalies are related to the phase separation of the metallic and insulator phase around the MI boundary.

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.