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Picene is a phenacene-type aromatic hydrocarbon molecule with five benzene rings. We have fabricated picene single crystal (SC) field-effect transistors (FETs) with solid gate and ionic liquid gate dielectrics. Although the picene SC FET showed a large hole-injection barrier without any modification of interface between source/drain electrodes and picene SC, such a large hole-injection barrier could be effectively reduced by modifying the interface with tetracyanoquinodimethane (TCNQ). Picene SC FET with an HfO2 gate dielectric and TCNQ-coated electrodes shows p-channel characteristics with a smooth hole injection and a field-effect mobility more than 1 cm2 V–1 s–1 in two-terminal measurement. Picene SC FET could be operated even in bottom-contact structure by modifying the interface with octanethiol. Furthermore, picene SC FET operated with ionic liquid gate dielectric, [1-butyl-3-methylimidazolium][hexafluorophosphate], showing the field-effect mobility of 1.8 × 10–1 cm2 V–1 s–1 and low absolute value, ...

The size and performance of a System LSI depend heavily on the architecture which is chosen. As a result, the architecture design phase is one of the most important steps in the System LSI development process and is critical to the commercial success of a device. In this paper, we propose a C-based variable length and vector pipeline (VVP) architecture design methodology and apply it to the design of the output probability computation circuit for a speech recognition system. VVP processing accelerated by loop optimization, memory access methods, and application-specific cir- cuit design was implemented to calculate the Hidden Markov Model (HMM) output probability at high speed and its performance is evaluated. It is shown that designers can explore a wide range of design choices and generate complex circuits in a short time by using a C-based pipeline architecture design method.

Thin film transistors (TFTs) with ionic liquid gate dielectrics, [1-ethyl-3-methylimidazolium][bis(trifluoromethanesulfonyl)imide] (emim[TFSI]) and [1-butyl-3-methylimidazolium][hexafluorophosphate] (bmim[PF 6 ]), are fabricated with thin films of one dimensional (1D) hydrocarbon, [7]phenacene. P-channel characteristics are observed for [7]phenacene TFTs with both ionic liquids by use of platinum electrode. The field-effect mobility μ for [7]phenacene TFT with bmim[PF 6 ] was recorded to be 0.28 cm 2 V −1 s −1 . The value of absolute threshold voltage, | V TH |, was less than 2.5 V, showing low-voltage operation. The accumulation of hole in the [7]phenacene TFTs with ionic liquids was confirmed from the voltage or time dependence of capacitance in metal–insulator-semiconductor structure, which shows that these TFTs operate electrochemically and the carriers are accumulated in the whole of [7]phenacene thin films.

Magnetic and dielectric properties have been investigated for Bi2CuO4, which has the same chemical formula as that of the parent materials of cuprate superconductors R2CuO4 (R: rare earths). Magnetization measurements show the antiferromagnetic transition of the Cu2+ spins at ∼42 K, as reported previously. Dielectric measurements for the frequencies of 1 kHz to 1 MHz show that the dielectric constants are 100–500 at room temperature. The dielectric dispersion reveals that the dielectric response lacks spatial coherence, a property which indicates the possible existence of phase separation as suggested for La2CuO4. The imaginary part of dielectric response gives the activation energy of 0.22 eV, suggesting that the dielectric response is governed by the electron hopping between the Cu ions.

A characteristic nonlinear electric responses were found in a charge ordered type ferroelectrics LuFe2O4 with less oxygen deficiency. Cole – Cole circular in the dielectric response varies in the function of the amplitude of the AC electric field. With a synchrotron radiation diffraction experiment under the current revealed the variation of the coherence length of the polar charge ordered W-layer along c-axis. The nonlinear response with the increase of the electronic current may relates to the electron hopping in the charge stripe structure.

O2 gas sensing behaviors are studied in picene thin film field-effect transistors (FETs) with hydrophobic polymer (Cytop™ or polystyrene) coated SiO2 gate dielectrics. Picene thin film FETs show a rapid reduction of hysteresis in transfer curves recorded in forward and reverse measurement modes, compared to a picene FET with hexamethydisilazane-coated SiO2. The picene FETs show very sensitive O2 gas sensing effects down to ∼10 ppm. A quantitative analysis is presented of the gate voltage (VG) dependent mobility induced by O2 exposure, i.e., the suppression of drain current at high VG.

New high-temperature superconductors continue to arrive on the scene — the most recent noteworthy additions being the iron arsenides — but there have been no new organic superconductors the past decade. Now the discovery of superconductivity at temperatures up to 18 K is reported in crystals of a simple hydrocarbon molecule doped with potassium or rubidium. The basis for the new compound is picene (C22H14), a molecule consisting of five benzene rings sharing edges with one another, which crystallizes into an ordered molecular solid. Intercalation of the alkali metals into the crystal lattice induces metallic behaviour and superconductivity in what is normally a semiconducting material. The Tc of 18 K in potassium-doped picene is high for an organic superconductor — only alkali-metal-doped C60 achieves higher. And as picene is one of a large family of molecules based on fused benzene rings, other superconducting hydrocarbons may be awaiting discovery. The phenomenon of superconductivity continues to intrigue, and several new superconducting materials have been discovered in recent years — but in the case of organic superconductors, no new material system with a high superconducting transition temperature has been identified in the past decade. Now it has been shown that the introduction of potassium into crystals of organic molecule picene can yield superconductivity at temperatures as high as 18 K. Efforts to identify and develop new superconducting materials continue apace, motivated by both fundamental science and the prospects for application. For example, several new superconducting material systems have been developed in the recent past, including calcium-intercalated graphite compounds1, boron-doped diamond2 and—most prominently—iron arsenides such as LaO1–xF x FeAs (ref. 3). In the case of organic superconductors, however, no new material system with a high superconducting transition temperature (Tc) has been discovered in the past decade. Here we report that intercalating an alkali metal into picene, a wide-bandgap semiconducting solid hydrocarbon, produces metallic behaviour and superconductivity. Solid potassium-intercalated picene (K x picene) shows Tc values of 7 K and 18 K, depending on the metal content. The drop of magnetization in K x picene solids at the transition temperature is sharp (

C60 and picene thin film field-effect transistors (FETs) in bottom contact structure have been fabricated with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) electrodes for a realization of mechanical flexible organic FETs. The C60 thin film FETs showed n-channel enhancement-type characteristics with the field-effect mobility μ value of 0.41 cm2 V−1 s−1, while the picene thin film FET showed p-channel enhancement-type characteristics with the μ of 0.61 cm2 V−1 s−1. The μ values recorded for C60 and picene thin film FETs are comparable to those for C60 and picene thin film FETs with Au electrodes.

We report dielectric and magnetic properties of a single crystal of LuFe 2 O 4 with different degrees of oxygen deficiency. The oxygen stoichiometry was monitored with the gas mixture ratio of CO 2 and CO during the crystal growing process. A sample having high resistivity of about 10 kΩ cm sample was found at room temperature. The relation between the control of the charge frustration and the completeness of the charge ordering is discussed.

Particle tracking technology is one of the most promising methods for the measurement of the velocity fluctuation of flows. It consists of the particle mask correlation (PMC) method and the KC method. The correlation coefficient calculation has the largest computational overhead in the PMC method. In this paper, a hardware of the correlation coefficient calculation is designed and accelerated by the zigzag tracing, the modification of the correlation coefficient equation, and parallel processing. The processing speed and circuit size of the design are evaluated.

Doping with the optimum concentration of carriers (electrons or holes) can modify the physical properties of materials. Therefore, improved ways to achieve carrier doping have been pursued extensively for more than 50 years. Metal-intercalation is one of the most important techniques for electron doping of organic / inorganic solids and has produced superconductors from insulators and metallic solids. The most successful examples are metal-intercalated graphite and C60 superconductors. Metal intercalation has been performed using solid-reaction and liquid solvent techniques. However, precise control of the quantity of intercalants in the target solids can be difficult to achieve using these methods, as that quantity depends largely on the initial conditions. Here we report an electrochemical method for metal-intercalation and demonstrate the preparation of superconductors using organic and inorganic materials (C60 and FeSe). The metal atoms are effectively intercalated into the spaces in C60 and FeSe solids by supplying an electric current between electrodes in a solvent that includes electrolytes. The recorded superconducting transition temperatures, Tc’s, were the same as those of metal-intercalated C60 and FeSe prepared using solid-reaction or liquid solvent techniques. This technique may open a new avenue in the search for organic / inorganic superconductors.

The phase diagram of the mixed donor quasi one-dimensional (Q1D) metallic system (TMTSF1−xTMTTFx)2PF6 has been studied. The study on the mixed donor systems helps us to establish not yet clarified phase boundaries in the Q1D system. We showed dependencies of properties on the donor mixing percentage for crystal parameters, resistivity, ESR (intensity and line width). ESR results show clear changes in the susceptibility and line width around 40 K. This result may indicate the existence of new boundary determined by the microscopic method on the Q1D phase.

High resolution X-ray structure analyses and electronic structure calculation revealed the condition for the charge ordering(CO) observed in the (TMTTF) 2 X (Fabre) salts. The phase diagram of the electronic states including 2k F and 4k F CO has been proposed associated with magnitudes of molecular dimerization and tetramerization.

We performed the low-temperature and radio-frequency (rf) ESR of spherically molded single crystals of β-p-NPNN in order to re-investigate the ferromagnetic resonance (FMR). The symmetric FMR signals were clearly observed below 0.8 K for the first time. The resonance field for H//c is markedly shifted about 80 G higher than the EPR resonance field while the anisotropy of the resonance field is very weak when the magnetic field is applied within the ab-plane. These results clearly indicate the spin-hard axis is parallel to the c-axis. We estimate the magnetic anisotropy HK = 61 G using the FMR relation with uniaxial anisotropy.

The low frequency (∼300 MHz) and low-temperature (0.4 K) ESR were performed in the γ-phase of p-NPNN, which is considered to be as a quasi-one-dimensional ferromagnet above the antiferromagnetic ordering temperature (0.65 K without a static magnetic field). Below 0.6 K, we succeeded in observing the antiferromagnetic resonance (AFMR) for the first time. The frequency–field relation is well reproduced by the two-sublattice model with orthorhombic anisotropy. In addition, we measured magnetic torque using small single crystal, which has the dimension of 0.25 × 0.10 × 0.10 mm3. A spin–flop transition and AF-paramagnetic (AF-P) transition are observed at 470 and 2100 G at 0.4 K, respectively. Both AFMR and magnetic torque measurements indicate that the spin-easy axis is almost parallel to the direction to phenyl ring from the ONCNO fragments.

The low-temperature structure analysis and low-temperature ESR were performed in the γ -phase of p -NPNN, which is considered to be as a quasi-one-dimensional ferromagnet above the antiferromagnetic ordering temperature (0.65 K without a static magnetic field). No structural phase transition was observed below 30 K, but we found the large thermal shrinkage between the intra-chain p -NPNN molecules along c -axis. This result suggests that the one-dimensionality of the ferromagnetic chain is effectively enhanced at lower temperature, since the geometry through NO-NO 2 contact gives rise to the strong ferromagnetic interaction. Below 0.6 K, we succeeded in observing the antiferromagnetic resonance (AFMR) using the low frequency (∼300 MHz) and low-temperature (0.5 K) ESR. The frequency-field relation is well reproduced by the two-sublattice model with orthorhombic anisotropy.

We study the anisotropy of ESR parameters using single crystal TDAE-C 60 , which has two polymorphisms: the one is ferromagnetic a-phase and the other is non-ferromagnetic α′-phase. In both α′- and α-phase, the line-widths and g-factors show anisotropic angular dependences at room temperature, such as ΔH pp b > ΔH pp c ∼ ΔH pp a and g c > g b = g a . The anisotropic behaviour of g-factors in both phases suggest the uniaxial rotation of Jahn-Teller distorted C 60 molecules around the c-axis, which is the close-packing direction of C 60 molecules. In the α′-phase the temperature dependence of g-factors has a clear anomaly around 160 K. Below this temperature, the observed g-factors are in-between the monovalent C 60 and TDAE + , indicating the restoration of missing TDAE spins. In the α-phase, the g-factors continuously shift with decreasing temperature, become anisotropic below 230 K, and show no remarkable anomaly at the structural phase transition temperature. These results suggest that the difference exists in the mixing between the wave functions of C 60 and TDAE, which is possibly developed by the structural difference between α′- and α-phases. This difference separates the magnetic peculiarities of two polymorphisms in TDAE-C 60 .

We found for the first time a structural phase transition in two-dimensional kagome antiferromagnet m - N -methylpyridinium α-nitronyl nitroxide ( m -MPYNN)·BF 4 ·\(\frac{1}{3}\) (acetone). As, below T s =128.7 K, the intense satellite reflections are clearly observed at the modulation wave vector of \(q_{\text{s}}=(\frac{1}{3},\frac{1}{3},0)\), the unit cell of the low-temperature phase is enlarged to \(\sqrt{3}a\times\sqrt{3}a\times c\). In the low-temperature phase, the space group is determined to be P 31 c . The orientation of acetone molecules orders below T s , leading to the lack of the three-fold axis. To confirm whether the low-temperature phase maintains a kagome -like network structure or not, we estimate the overlap integrals between the singly occupied molecular orbital wave functions of the MPYNN molecules by the extended Huckel method. The result is that all the overlap integrals are modified below T s , suggesting that the system below T s cannot be regarded as the uniform S =1 kagome ant...

Ultrafast terahertz response of charge ordering (CO) in LuFe2O4 was investigated by near-infrared-pump (1.55 eV) and terahertz-probe (2–9 meV) spectroscopy. Photoinduced absorption observed immediately (1 ps) after the photoexcitation was attributed to photoinduced melting of the CO. The charge dynamics thereafter can be characterized by subsequent development of the photoinduced conductivity in the low-energy region (2–3 meV), implying the formation of a metallic state.

We give an overview of our studies on the electron spin resonance (ESR) in the hexagonal triangular antiferromagnets of ABX 3 type using millimeter and submillimeter waves and static and pulsed high magnetic fields. Novel ESR modes, which cannot be understood by the conventional theory of the antiferromagnetic resonance, were observed. Examples of this include that there exists the gapless excitation even for the easy-axis anisotropy. The ESR modes can be classified by the signs of the exchange interaction J 0 along the c-axis and the anisotropy. The ESR modes were calculated within the framework of the mean-field approximation using three-sublattice and six-sublattice models for the ferromagnetic and antiferromagnetic J 0 interaction, respectively. The experimental results were well described by the present calculations.

We present the ESR system with dielectric resonators for performing the high-pressure measurements. This system is constructed by combining the diamond anvil cell (or sapphire anvil cell) with the double-stacked dielectric resonators, which are commercially available. The maximum pressure is obtained to be about 15 kbar and this high-pressure ESR system holds its availability from room temperature to Liq. He temperature. This system has a potential to perform ESR measurements under high-pressure with high accuracy. As an example, we show its application to the polymerization in the TDAE–C 60 organic ferromagnet under high pressure.

LuFe${}_{2}$O${}_{4}$ is being actively studied in the context of an unconventional electronic ferroelectricity that appears due to charge ordering of $F\phantom{\rule{0}{0ex}}{e}^{2+}$ and $F\phantom{\rule{0}{0ex}}{e}^{3+}$ oxidation states. LuFe${}_{2}$O${}_{4}$ displays a high magneto-electric coupling, giant magnetic coercivity, and other unusual features, some of them highly controversial. In this study a group of researchers from Japan present their XMCD results in pulsed magnetic fields reaching 30 Tesla. Their technique allows them to measure valence-specific magnetization of $F\phantom{\rule{0}{0ex}}{e}^{2+}$ and $F\phantom{\rule{0}{0ex}}{e}^{3+}$ ions above and below the charge-ordering temperature and provides a unique view on the coupling between the charge and spin degrees of freedom in LuFe${}_{2}$O${}_{4}$.

The mineral tetrahedrite Cu$_{12}$Sb$_{4}$S$_{13}$ exhibits a first-order metal--insulator transition (MIT) at $T_{\rm MI}$ = 85 K and ambient pressure. We measured the $^{63}$Cu-NMR at ambient pressure and the resistivity and magnetic susceptibility at high pressures. $^{63}$Cu-NMR results indicate a nonmagnetic insulating ground state in this compound. The MIT is monotonically suppressed by pressure and disappears at $\sim1.0$ GPa. Two other anomalies are observed in the resistivity measurements, and the pressure -- temperature phase diagram of Cu$_{12}$Sb$_{4}$S$_{13}$ is constructed., Comment: 5 pages, 7 figures

System level design study group in EDA technical committee of JEITA has researched the trends of system level design technologies from various aspects of views so as to define an ideal design flow and methodology. The results of the investigations consist of (1) problems and requirements from system level designers (needs), (2) current status of system level design tools (seeds), (3) standardization activities for system level design languages, and so on. They also proposed a desirable system level design flow taking account of the needs and the seeds. In this paper, we introduce the summary of their works. After that, I describe an approach to a C-based architecture design, called Bach, which we have developed. The features of the Bach system are (1) C-based user language with untimed semantics which is suitable for large-scale circuit design, (2) a fast bit-accurate simulator at the C level, (3) a high level synthesizer which can compile a program describing the untimed behavior of hardware into RTL VHDL. Using the example of an MPEG-4 video codec design, we summarize its design flow and effects.

The reaction of a tripodal ligand (H2L = N,N-bis(2-hydroxybenzyl)-N′,N′-dimethylethylenediamine) with Cu(NO3)2·3H2O and Cu(ClO4)2·6H2O in methanol yielded [Cu2(HL)2](NO3)2·H2O (1) and [Cu2(HL)2](ClO4)2 (1′), respectively. When H2L was allowed to react with CuSO4·5H2O in the presence of triethylamine (1 ∶ 1 ∶ 2) in methanol, the neutral dicopper(II,II) complex [Cu2(L)2] (2) was obtained. The monopositive species [Cu2(L)(HL)]ClO4·CH3OH·H2O (3) crystallized on mixing 1′ and 2 (1 ∶ 1) in methanol–dichloromethane. The crystal structures of 1, 2, and 3 were determined by X-ray crystallography. All of the complexes consist of a discrete dinuclear molecule with bis(μ-phenoxide)-bridges. The tripodal ligand functions as a tetradentate ligand and one of the phenolic oxygen atoms serves as a bridging ligand. Protonation/deprotonation takes place at the terminal phenol moiety and as the phenol group is deprotonated the coordination geometry changes from a distorted square pyramid to a distorted trigonal bipyramid. The two copper ions in 1–3 are antiferromagnetically coupled with 2J = −714 (1), −19.9 (2), and −277 cm−1 (3). The results clearly demonstrate that protonation/deprotonation causes a change in coordination geometry, which in turn drastically affects magnetic exchange interactions.

The pressure dependence of the superconducting transition temperature (Tc) and unit cell metrics of tetragonal (NH3)yCs0.4FeSe were investigated in high pressures up to 41 GPa. The Tc decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The Tcvs. c plot is compared with those of various (NH3)yMxFeSe (M: metal atoms) materials exhibiting different Tc and c, showing that the Tc is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the Tc. No superconductivity was observed down to 4.3 K in (NH3)yCs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the Tc reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, Tc slowly decreased with increasing pressure above 21 GPa and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe.

We report here the direct evidence of the existence of a permanent electric dipole moment in both crystal phases of a fullerene-based magnet--the ferromagnetic α-phase and the antiferromagnetic α'-phase of tetra-kis-(dimethylamino)-ethylene-C60 (TDAE-C60)--as determined by dielectric measurements. We propose that the permanent electric dipole originates from the pairing of a TDAE molecule with surrounding C60 molecules. The two polymorphs exhibit clear differences in their dielectric responses at room temperature and during the freezing process with dynamically fluctuating electric dipole moments, although no difference in their room-temperature structures has been previously observed. This result implies that two polymorphs have different local environment around the molecules. In particular, the ferromagnetism of the α-phase is founded on the homogeneous molecule displacement and orientational ordering. The formation of the different phases with respect to the different rotational states in the Jahn-Teller distorted C60s is also discussed.

Resizing is an operation where expansion or contraction of the pattern is performed. Large numbers of patterns that compose the mask pattern of ICs have closed regions confined by edges which are parallel to the x- or y-axis; but to increase the density of integration and improve the circuit performance, we sometimes have to use diagonal edges. For resizing of such mask patterns, we here propose a resizing algorithm in which a group of patterns containing some diagonal edges is processed in a calculation time of O(N log N ) for N vertices. In this algorithm, intermediate sequences of vertices, known as provisional figures, are generated from the input figures, and the output figures are obtained by ORing these provisional figures. This method has the merit that the algorithm can be simplified and faster processing is possible with the help of provisional figures. © 2001 Scripta Technica, Electron Comm Jpn Pt 3, 84(5): 62–74, 2001

Annealing effects on the magnetic and structural properties of single-crystal TDAE-C-60 are investigated. When a crystal is well-annealed at 350 K, ferromagnetic ordering takes place below 16 K, though no magnetic phase transition is shown in as-grown crystal. The saturated magnetization was obtained to be 0.9+/-0.1 mu(B) per C-60. It was first found that the well-annealed crystal shows a structural phase transition around 180 K, probably associated with the orientational ordering of C-60 molecules. On the other hand, the as-grown crystal undergoes no structural phase transition at least down to 30 K while the motion of C-60 molecules is restricted below around 150 K. The possible relation between the low-temperature structure and the magnetic ordering is discussed.

Temperature dependence of electron spin resonance in Na2C60 was studied in a temperature range from 2 to 350 K. It was shown that Na2C60 was metallic above 50 K and had a metal-insulator transition at 50 K. The center frequency for the Hg(2) Raman mode in Na2C60 at 298 K was close to those in the metallic Rb3C60, K3C60, and Cs3C60, while the linewidth was close to that in the metallic but nonsuperconducting Cs3C60. The Hg(2) mode showed a large blueshift and narrowing at 50 K. The center frequency and the linewidth in the low-temperature region from 50 K were almost the same as those in the insulating C-60 and Rb6C60, which showed the metal-insulator transition at 50 K in Na2C60. The origin of this metal-insulator transition was discussed in terms of the electron-phonon interaction (Jahn-Teller effect) and the electron-electron interaction (Mott-Hubbard picture). [S0163-1829(99)04123-5].

Laser-induced photodissociation of ozone molecules is studied by irradiating isotope-mixed ozone gas with a narrow-band laser beam of around 1 μm wavelength. Significant decomposition is detected only for the irradiated ozone isotopologue with the decomposition amount nearly proportional to the laser power. This result indicates that the process is not due to multi-photon absorption, but rather due to single-photon absorption through the rotationally resolved transitions in the 3 A 2 ← 1 A 1 ( v 2 = 1–0) band.

The electron spin resonance (ESR) at low frequency (0.6–3 GHz) and at low temperature ( ∼ 0.5 K) was performed for the single molecular magnet V 15 . Non-linear field dependence of resonance at the lowest temperature implies the existence of the zero-field gap. The angle dependence of resonance field has strong anisotropy. We directly estimate the zero-field energy gap of 30 mK and analyze the energy levels using the model with Dzyaloshinskii–Moriya interaction.

The magnetization measurements under pressure were performed on the fullerene-based ferromagnet, α -TDAE- C 60 . We found that the saturation magnetization below the ferromagnetic ordering temperature T c is rapidly suppressed with increasing pressure and disappeared above P c 2 = 0.1 – 0.2 GPa . This pressure is remarkably lower than the critical pressure of polymerization P c = 0.7 GPa . On the contrary, T c is almost pressure independent below P c 2 , but, above P c 2 , could not be entirely determined because of the strong suppression of the magnetization. In the paramagnetic region, the susceptibility under pressure indicates the total number of spins remains unchanged around P c 2 as well as P c . We discuss these results compared with the high-pressure ESR.

ESR measurements have been performed on KCuCl3 and TlCuCl3 in the frequency range up to 762 GHz and field range up to 30 T at helium temperatures. The exchange network in the present systems is described as an S= 1 2 Heisenberg spin ladder along the a-axis with an additional diagonal interaction. Both compounds have a singlet ground state with an excitation gap. In KCuCl3, two kinds of transitions are observed between the ground state and the excited triplet states. They correspond to the excitations at Q=(1, 0, 1) and (0.5, 0, 1) with the excitation energies Δ≈640 and 1080 GHz, respectively. When the external field is increased, the frequency of the lowest branch with the zero-field gap Δ≈640 GHz decreases linearly with a tendency toward zero at Hc≈22 T. In TlCuCl3, a transition from the singlet ground state to the excited triplet state is observed. The zero-field gap is determined as Δ≈160 GHz.

Submillimeter wave ESR measurements of the ABX 3 triangular antiferromagnet CsMnBr 3 with easy-plane type anisotropy have been performed in the frequency region from 9 to 383.3 GHz. The frequency-field relations of AFMR observed below T N =8.3 K are analyzed by the molecular field theory using six sublattice model. To explain the AFMR modes, it is necessary to consider the diagonal interchain interaction J 2 as in the cases of the easy-axis type triangular antiferromagnets.

Alkali-metal-intercalated FeSe materials, (NH3)(y)M0.4FeSe (M: K, Rb, and Cs), have been synthesized using the liquid NH3 technique. (NH3)(y)Cs0.4FeSe shows a superconducting transition temperature (T-c) as high as 31.2 K, which is higher by 3.8 K than the T-c of nonammoniated Cs0.4FeSe. The T(c)s of (NH3)(y)K0.4FeSe and (NH3)(y)Rb0.4FeSe are almost the same as those of nonammoniated K0.4FeSe and Rb0.4FeSe. The T-c of (NH3)(y)Cs0.4FeSe shows a negative pressure dependence. A clear correlation between T-c and lattice constant c is found for ammoniated metal-intercalated FeSe materials, suggesting a correlation between Fermi-surface nesting and superconductivity.

International audience; We report nonlinear conductivity associated with a phase transition in polar charge ordered material YbFe2O4. To investigate the existence of nonlinear conductivity, we measured temperature dependence of conductivity as a function of applied electric current and estimated the sample heating precisely. Then we found the nonlinear conductivity below three dimensional charge ordering temperature 340 K. The result is consistent with diffraction observation.

Electron Spin Resonance (ESR) measurements have been performed on axial triangular antiferromagnets CsNiBr 3 and CsMnI 3 in their lowest three-dimensional (3 D) ordered phase. The frequency vs. magnetic field diagrams are obtained in the frequency range from 9 to 380 GHz and the magnetic field up to 160 kOe. Several significant disagreements between the experimental data and the theory based on the conventional model are found. It is shown that the disagreements can be removed by the diagonal interchain exchange coupling J 2 . The ESR theory is developed taking the J 2 coupling into account. Fitting the present theory to experimental data, the interaction parameters of CsNiBr 3 and CsMnI 3 are determined.

We carefully examined ESR and magnetic susceptibility around T s =128.7 K , at which the structural phase transition takes place, of m-MPYNN BF4 1 3 acetone. Both the ESR parameters and the magnetic susceptibility have a clear anomaly around Ts. The g-factor shows a clear shift around Ts independently of the shape of the samples. It possibly corresponds to the shift of MPYNN molecules accompanied by the structural phase transition. Moreover, the Weiss temperature is obtained to be +22.7 K above Ts and +3.42 K below Ts, respectively. These results suggest that the lattice distortion plays an important role on the low-temperature spin-gap state.

The magnetocapacitance effect was investigated using impedance spectroscopy on single crystals of LuFe(2)O(4). The intrinsic impedance response could be separated from the interfacial response and showed a clear hysteresis loop below T(Ferri)∼240 K under the magnetic field. The neutron diffraction experiment under the magnetic field proves the origin of the dielectric property related to the motion of the nanosized ferromagnetic domain boundary. These results imply that the modification of the microscopic domain structure is responsible for the magnetoelectric effect in LuFe(2)O(4).

We report the observation of zero resistivity (\ensuremath{\rho}) in a hydrocarbon superconductor, and describe the temperature dependence of \ensuremath{\rho} in metal-doped hydrocarbons. The resistivity of K-doped picene (K${}_{x}$picene) has been recorded from pellet samples in a four-terminal measurement mode. A drop in $\ensuremath{\rho}$ is observed below 7 K for K${}_{3.1}$picene and below 11 K for K${}_{3.5}$picene, which clearly displays zero resistivity. The resistivity drop at 7 K is consistent with the superconducting critical temperature (${T}_{\mathrm{c}}$) obtained from the magnetic susceptibility of the 7 K phase of K${}_{3}$picene, while the drop at 11 K is inconsistent with the ${T}_{\mathrm{c}}$'s of both the 7 and 18 K phases of K${}_{3}$picene reported previously. The temperature dependence of \ensuremath{\rho} for both samples exhibits granular-metal-like behavior in the normal state.

Potassium-doped picene (K3.0picene) with a superconducting transition temperature (T C) as high as 14 K at ambient pressure has been prepared using an annealing technique. The shielding fraction of this sample was 5.4% at 0 GPa. The T C showed a positive pressure-dependence and reached 19 K at 1.13 GPa. The shielding fraction also reached 18.5%. To investigate the chemical composition and the state of the picene skeleton in the superconducting sample, we used energy-dispersive x-ray (EDX) spectroscopy, MALDI-time-of-flight (MALDI-TOF) mass spectroscopy and x-ray diffraction (XRD). Both EDX and MALDI-TOF indicated no contamination with materials other than K-doped picene or K-doped picene fragments, and supported the preservation of the picene skeleton. However, it was also found that a magnetic K-doped picene sample consisted mainly of picene fragments or K-doped picene fragments. Thus, removal of the component contributing the magnetic quality to a superconducting sample should enhance the volume fraction.

This article reviews new superconducting phases of carbon-based materials. During the past decade, new carbon-based superconductors have been extensively developed through the use of intercalation chemistry, electrostatic carrier doping, and surface-proving techniques. The superconducting transition temperature T c of these materials has been rapidly elevated, and the variety of superconductors has been increased. This review fully introduces graphite, graphene, and hydrocarbon superconductors and future perspectives of high-T c superconductors based on these materials, including present problems. Carbon-based superconductors show various types of interesting behavior, such as a positive pressure dependence of T c. At present, experimental information on superconductors is still insufficient, and theoretical treatment is also incomplete. In particular, experimental results are still lacking for graphene and hydrocarbon superconductors. Therefore, it is very important to review experimental results in detail and introduce theoretical approaches, for the sake of advances in condensed matter physics. Furthermore, the recent experimental results on hydrocarbon superconductors obtained by our group are also included in this article. Consequently, this review article may provide a hint to designing new carbon-based superconductors exhibiting higher T c and interesting physical features.

The magnetic properties of single crystal TDAE-C 70 -toluene are reported in relation to its unique dimerized structure of C 70 molecules in the unit cell. The g -factor at room temperature ( g =2.0052) suggests that the origin of the magnetism is different from C 70 ( g =2.002). The spins on the C 70 molecules are cancelled out due to the dimerization. No magnetic phase transition appears at least down to 0.5 K. The magnetic susceptibility follows the Curie–Weiss law with the Weiss constant of +0.36 K. These results show that the weakly coupled spins on TDAE molecules contribute the magnetism of this salt, which is in contrast to the ferromagnetic TDAE-C 60 where the TDAE spins are cancelled.

We report electronic structure and physical properties of metal doped picene as well as selective synthesis of the phase exhibiting 18 K superconducting transition. First, Raman scattering is used to characterize the number of electrons transferred from the dopants to picene molecules. The charge transfer leads to a softening of Raman scattering peaks, which enables us to determine the number of transferred electrons. From this we have identified that three electrons are transferred to each picene molecule in the superconducting doped-picene solids. Second, we report the pressure dependence of Tc in 7 and 18 K phases of K3picene. The 7 K phase shows a negative pressure-dependence, while the 18 K phase exhibits a positive pressure-dependence which cannot be understood with a simple phonon mechanism of BCS superconductivity. Third, we report a new synthesis method for superconducting K3picene by a solution process with monomethylamine, CH3NH2. This method enables one to prepare selectively the K3picene sample exhibiting 18 K superconducting transition. The discovery of suitable way for preparing K3picene with Tc = 18 K may facilitate clarification of the mechanism of superconductivity.

The magnetocapacitance effect was investigated using impedance spectroscopy on single crystals of LuFe(2)O(4). The intrinsic impedance response could be separated from the interfacial response and showed a clear hysteresis loop below T(Ferri)∼240 K under the magnetic field. The neutron diffraction experiment under the magnetic field proves the origin of the dielectric property related to the motion of the nanosized ferromagnetic domain boundary. These results imply that the modification of the microscopic domain structure is responsible for the magnetoelectric effect in LuFe(2)O(4).