Search

Implantable cardioverter defibrillators are implanted in children to prevent sudden death due to life-threatening ventricular arrhythmias. Transvenous electrode placement is difficult for children because of the small vessel size. Especially, defibrillator electrode placement requires other innovative techniques. We successfully implanted a defibrillator electrode in the pleural cavity using a thoracoscopic approach for a 4-year-old child with sodium channelopathy.

Background A specific walking speed minimizing the U-shaped relationship between energy cost of transport per unit distance (CoT) and speed is called economical speed (ES). To investigate the effects of reduced body weight on the ES, we installed a body weight support (BWS) apparatus with a spring-like characteristics. We also examined whether the 'calculated' ES was equivalent to the 'preferred' walking speed (PWS) with 30% BWS. Methods We measured oxygen uptake and carbon dioxide output to calculate CoT values at seven treadmill walking speeds (0.67–2.00 m s− 1) in 40 healthy young males under normal walking (NW) and BWS. The PWS was determined under both conditions on a different day. Results A spring-like behavior of our BWS apparatus reduced the CoT values at 1.56, 1.78, and 2.00 m s− 1. The ES with BWS (1.61 ± 0.11 m s− 1) was faster than NW condition (1.39 ± 0.06 m s− 1). A Bland-Altman analysis indicated that there were no systematic biases between ES and PWS in both conditions. Conclusions The use of BWS apparatus with a spring-like behavior reduced the CoT values at faster walking speeds, resulting in the faster ES with 30% BWS compared to NW. Since the ES was equivalent to the PWS in both conditions, the PWS could be mainly determined by the metabolic minimization in healthy young males. This result also derives that the PWS can be a substitutable index of the individual ES in these populations.

The complex dielectric constant of semicrystalline form II polyvinylidene fluoride (PVDF (II)) in the frequency range from 0.2 to 6.0 THz has been determined by broadband terahertz time-domain spectroscopy (THz-TDS). The obtained dielectric constant consists of superposition of four vibration modes at 1.60, 2.36, 3.04 and 5.31 THz of crystalline part and a broad relaxation mode with center frequency of 0.68 THz which will be attributed to boson peak of amorphous fraction. In addition, the temperature dependence of the dielectric constant has also been measured, and we have determined the glass transition temperature of amorphous fraction of PVDF (II) as about 192 K by analysis of the temperature variation of peak frequency of the lattice vibration mode.

We present a case of a high-risk 19-year-old female with long-QT syndrome (LQTS) with compound mutations. She had a history of aborted cardiac arrest and syncope and had received treatment with propranolol for 15 years. However, because she developed adult-onset asthma we tried to switch propranolol, a nonselective beta-blocker, to beta-1-cardioselective agents, bisoprolol and metoprolol. These resulted in both a markedly prolonged corrected QT interval and the development of LQTS-associated arrhythmias. Eventually, propranolol was reinitiated at a higher dose with the addition of verapamil, and she has had no further cardiac or asthmatic events for 5 years.

Muon-spin rotation (mu SR) measurements have been used to study the superconducting vortex properties of the organic superconductors kappa-(BEDT-TTTF)(2) Cu(SCN)(2), alpha-(BEDT-TTF)(2) NH4Hg(SCN)(4) and beta-(BEDT-TTF)(2)IBr2. These materials all have highly anisotropic structures consisting of metallic layers of BEDT-TTF molecules alternating with less well conducting anion layers. Varying the anion gives rise to a change in the anisotropy of the superconductivity and also to changes in the superconducting transition temperature. We have used both transverse and longitudinal magnetic fields to study the three-dimensional flux line lattice that is present at low temperatures and fields and to study also the loss of flux lattice order that occurs on increasing the temperature and field. (C) 2000 Elsevier Science B.V. All rights reserved.

Four types of functionalized 3,3'-bicarbazole derivatives are prepared and investigated as a host material for blue phosphorescent OLEDs. By using a 3,3'-bicarbazole derivative/FIrpic film as an emissive layer, high power efficiency of 46 lm W(-1) (45 cd A(-1), EQE 20%) with an extremely low driving voltage at 3.1 V is obtained at 100 cd m(-2).

We Review Our Dynamical Property Measurements of Rattling Phonons in Type-I Clathrate Compounds, the Quasi-on-Center Ba8Ga16Ge30 (BGG) and Off-Center Ba8Ga16Sn30 (BGS), Using a Terahertz Time-Domain Spectrometer. The Lowest-Lying Vibrational Modes of Rattling Ba Ions in the Oversized Cage Show Anomalous Temperature Dependence in their Spectra. For BGG, the Temperature Dependence Is Mostly Consistent with a Local Anharmonic Potential Approximation that Predicts Softening towards Low Temperature. On the other Hand, for BGS, a Single Broad Peak of Off-Center Rattling Phonons Splits into Two Subpeaks below 120 K, and, with Further Lowering Temperature, the Spectra Show Anomalous Broadening. While the Splitting Can Be Understood by the Double Well Potential, the Linewidth Broadening Must Be Attributed to some Relevant Interactions with such Excitations as Acoustic Phonons and Doped Carriers.

Background. Hyponatremia (HN) is relatively common in adults with congenital heart disease and is a powerful predictor of mortality. However, the precise relationship of HN to the Fontan pathophysiology remains unknown. Purpose. Our study aimed to clarify the association of HN to the Fontan pathophysiology. Methods and Results. We measured the plasma sodium (Na) level in 169 consecutive Fontan patients (78 children) and HN (≤137 mEq/L) was observed in 50 patients (30% of the total patients, 31% of the children). The HN patients showed a lower peak oxygen uptake (VO2) with a greater New York Heart Association class (P < .0001). The plasma level of norepinephrine (NE), rennin activity (PRA), arginine vasopressin, central venous pressure (CVP) and medications were associated with the Na levels and the NE, PRA, and diuretic use were the independent determinants (P < .01−.0001). The plasma B-type natriuretic peptide was not correlated with the Na levels. In the children, diuretic use and the PRA independently determined the Na levels without any association to the CVP or peak VO2. During a median follow-up of 2.1 years, the HN in addition to the CVP and peak VO2 independently predicted the unscheduled hospitalizations in all patients, while the HN was the only independent predictor of the hospitalizations in the adult patients (hazard ratio: 3.1, 95% confidence interval 1.2–8.0, P= .021). Conclusions. Child and adult Fontan patients exhibited a high prevalence for HN that closely reflected some neurohumoral activation and predicted adverse clinical events, especially in adult Fontan patients.

Temperature dependence of the complex dielectric constant at 16.3 GHz has been measured on dry poly(dA)–poly(dT) DNA with Na + counterions under different relative humidity (RH). The rotational motion of sole water dipoles hydrated in PO 2 − is detected at low RH, and the collective motion due to water network in major groove is successfully observed at high RH. From the infrared (IR) spectroscopy in dry DNA introducing metallic ions (M-DNA), the symmetric and antisymmetric stretching bands of PO 2 − distinctly depend on RH and type of metallic ions. The IR spectral change indicates that the monovalent ions (Li and Na) are arranged in PO 2 − though the divalent and trivalent ions connect to the base molecules.

The isostructural series of two-dimensional (2-D) fishnet-type network compounds, [{Ru(2)(O(2)CCF(3))(4)}(2)(TCNQR(x))] x n(solv) (R(x) = H(4), 1; Br(2), 2; Cl(2), 3; F(2), 4; F(4), 5), has been synthesized from the reactions of a paddlewheel diruthenium(II, II) complex, [Ru(2)(II,II)(O(2)CCF(3))(4)], and neutral TCNQ derivatives (TCNQR(x) = 2,3,5,6- or 2,5-halogen-substituted 7,7,8,8-tetracyanoquinodimethane) under anaerobic conditions. Corresponding Rh compounds 1-Rh-5-Rh, which are diamagnetic and redox-inactive, were also synthesized for the purpose of comparison with 1-5. According to the electron affinity of TCNQR(x), which is related to its first reduction potential, the Ru(2) series (1-5) has the requisite driving force for charge transfer from [Ru(2)(II,II)(O(2)CCF(3))(4)] to TCNQR(x), which can lead to a mixed-valence state of [{Ru(2)(4.5+)}-(TCNQR(x)(*-))-{Ru(2)(4.5+)}] for the 2-D network. Such a charge (or electron) transfer results in magnetic exchange interactions between [Ru(2)] units (S = 1 for [Ru(2)(II,II)] and S = 3/2 for [Ru(2)(II,III)](+)) via TCNQR(x)(*-) S = 1/2 radicals that lead to long-range magnetic ordering in the layer. In the present series, only 5 demonstrated the full electron transfer (1-e(-) transfer) to the mixed-valence state, whereas other members are essentially in the state [{Ru(2)(4+)}-(TCNQR(x)(0))-{Ru(2)(4+)}]. Whereas 1-4 are paramagnetic, 5 is a metamagnet undergoing 3-D long-range antiferromagnetic ordering at 95 K (= T(N)) and reverts to a magnetic-field-induced ferromagnetic state exhibiting coercivity up to 60 K. This result is consistent with the fact that TCNQF(4) has the strongest electron affinity among the TCNQR(x) molecules. Even in neutral forms, however, 1-4 can be observed to undergo thermally and/or field-activated charge transfers from [Ru(2)(II,II)] to TCNQR(x) to give semiconductors with an activation energy of 200-300 meV, which is a driving force to transport electrons over the lattice. As determined by their conducting properties, the ease of thermally and/or field-activated charge transfers is on the order of 142 approximately = 35, which is in agreement with the order of electron affinity of TCNQR(x). Indeed, a magnetic anomaly with short-range order associated with the localization of charge-transferred electrons was revealed in the low-temperature susceptibility data for 2 and 3. Finally, 5 was subjected to terahertz time-domain spectroscopy, the data from which revealed that transport hopping electrons scattered at high temperatures interact with magnetically ordered spins with the scattering being suppressed at T(N), at which temperature the real part of the complex electronic conductivity (sigma(1)) and dielectric permeability (epsilon(1)) are dramatically altered. From these collective data, we conclude that molecular design based on an interunit charge transfer in a paramagnetic lattice is an efficient route to the design of materials with synergism between magnetic and conducting properties.

Two isotypic borophosphates MBPO{sub 4}(OH){sub 2} (M=Mg, Ni) have been hydrothermally synthesized and structurally characterized by powder X-ray diffraction in the space group P3{sub 1}21. Nickel (or magnesium) atoms are octahedrally coordinated. The octahedra share edges to form helix chains around the three-fold screw-axis. Boron and phosphorus atoms are both tetrahedrally coordinated. The BO{sub 4} and PO{sub 4} tetrahedra are alternately connected, forming vierer-single chains. These two kinds of chains are intersected in the three-dimensional framework structure. NiBPO{sub 4}(OH){sub 2} can be considered as a quasi-one-dimensional magnet because the shortest Ni{sup 2+}-Ni{sup 2+} distance within the helix chain is about 3.187(1) A, while the shortest inter-chain connection of the nickel ions is through a BO{sub 4} group (5.650(1) A). Both dc and alternating current (ac) susceptibilities and isothermal magnetization have been measured on powder sample. The intra- and inter-chain interactions are proved to be both ferromagnetic, and a long-range ordering is established below 2.2 K in NiBPO{sub 4}(OH){sub 2}. - Graphical abstract: Two isotypic borophosphates MBPO{sub 4}(OH){sub 2} (M=Mg, Ni) have been hydrothermally synthesized and structurally characterized by powder X-ray diffraction in the space group P3{sub 1}21. Nickel (or magnesium) atoms are octahedrally coordinated, which further share edges forming NiO{submore » 6} chains around the three-fold screw-axis. Magnetic investigation of NiBPO{sub 4}(OH){sub 2} shows that it is a quasi-one-dimensional magnet, where the intra- and inter-chain interactions are proved to be both ferromagnetic, and a long-range ordering is established below 2.2 K.« less

The title BETS salt is a quasi-two-dimensional paramagnetic metal with a high-spin localized at the FeIII site in the tetrahedral anion FeCl4. At TMI = 8.3 K, however, it undergoes a metal-to-insulator transition spontaneously associated by antiferromagnetic (AFM) and ferroelectric-like orders, and also by the structural transition. An application of a high magnetic field makes this insulator unstable against reentering the metallic state, followed at higher fields by a transition to the superconducting state. These unique properties totally indicate noticeable spin- and charge-correlation of π electrons in the crystal lattice with localized d-spins. This article reviews these phenomena focusing on the AFM insulating states and high-temperature metallic states exhibiting a multifunctional interplay among the conductivity, magnetism and dielectricity. Discussions will be made on the anomalous metallic state, in comparison with the isostructural, superconductor GaCl4 salt exhibiting contrasting anomalies in the metallic state.

We have investigated the microwave response at 45 GHz in an organic superconductor λ-(BEDT-TSF) 2 GaCl 4 with T c = 4.8 K. We determine the μ 0 H c2 – T phase diagram from microwave loss and find that the superconducting state is in the pure limit ( l / ξ GL ∼ 10). Although the real part of the complex conductivity (= σ 1 + i σ 2 ) does not show a coherence peak just below T c , the London penetration depth completely saturates at low temperatures down to T / T c = 0.2, which may provide an evidence for a conventional s-wave pairing. In the metallic state below about 50 K, σ 1 c (parallel to the c -axis) deviates downward from σ dc c , while σ 2 , which should be zero in a conventional metal, increases exponentially toward T c . In spite of the fact that the Hagen–Rubens limit is well satisfied as far as the dc conductivity is concerned, a Drude model is unable to explain the large positive σ 2 . In order to explain such anomalies in the metallic state, we propose a possible existence of so-called a pseudogap near a Fermi level. The anomalous increase of the positive σ 2 may be attributed to an appearance of pre-formed electron pairs in the pseudogap state. This appearance can be regarded as a precursor to the superconducting transition. Such a precursory phenomenon has been observed also in the isostructural FeCl 4 salt with the anomalous metallic states, which shows a negative σ 2 in contrast to the GaCl 4 salt. Just the opposite of ground states in between the GaCl 4 and FeCl 4 salts may result in the contrasting anomalous metallic states with different precursory phenomena with opposite signs of σ 2 .

We have investigated the 45 GHz microwave response from an organic superconductor λ-(BEDT-TSF)2GaCl4 with T c = 4.8 K. In the superconducting state, the London penetration depth saturates well below T c , which may provide an evidence for a conventional s-wave paring. In the metallic state, σ 1 c deviates downward from σ dc c , while σ 2 c , which should be zero in a conventional metallic state, increases exponentially toward T c . This anomalous metallic state has been discussed in terms of a possible formation of incoherent electron pairs in so-called a pseudogap state.

Two solid solutions, La4Cu(3-x)Zn(x)MoO12 (0.05or = xor = 0.20, SS1) and La4Cu(3-x)Zn(x)MoO12 (0.30or = xor = 2.40, SS2), were synthesized at ambient pressure and at temperatures from 1025 to 1200 degrees C by traditional solid-state reactions. Their structures were determined from X-ray powder diffraction with the help of electron and neutron diffraction. The atomic arrangements of SS1 and SS2 are similar, but their space groups are different, Pmnm for SS1 and P-1 for SS2, respectively. The copper, zinc, and molybdenum are coordinated by oxygen in corner-sharing trigonal bipyramids that are sandwiched between layers of lanthanum cations. In the transition metal cations layer of SS2, the copper and zinc cations order into a Kagomé-like lattice of triangular clusters. The magnetism has been measured from 2 to 300 K and is highly influenced by the geometric arrangement of the Cu(II) and Zn(II) cations. The number of free electrons per three Cu atoms is close to one for all samples in SS1 and SS2 indicating that the system can be well expressed by independent Cu(II)3 clusters. Spontaneous magnetization was observed in the system.

Electron spin resonance experiments with 15 GHz microwave have been performed on λ-(BEDT-TSF)2Fe1-xGaxCl4 (x = 0 and 0.4) single crystals at the various different temperatures down to 1.5 K. For λ-(BEDT-TSF)2FeCl4, the g-value do not show the symmetric angular dependencies of the magnetic field direction with respect to the conducting ac-plane at several temperatures above 20 K. This means that the observed signals are not mainly due to π-electrons in BEDT-TSF molecules but to (d-electrons of Fe ions. The line width for H//a* and H//c increases with decreasing temperature from 200 to 70 K. This might be correlated to the anomaly in the dielectric response at 70 K reported earlier. For λ-(BEDT-TSF)2Fe0.6Ga0.4Cl4, the large enhancement of the g-value below 120 K and the peak of the line width at around 95 K are observed. These anomalies suggest the possible anomaly in the electronic states as in the case of λ-(BEDT-TSF)2FeCl4. An enhancement of the line width associated with the antiferromagnetic transition is observed both for λ-(BEDT-TSF)2FeCl4 and λ-(BEDT-TSF)2Fe0.6Ga0.4Cl4.

We performed precise X-ray diffraction measurements on an organic conductor, λ-(BETS) 2 FeCl 4 , with synchrotron radiation, where BETS is bis(ethylendithio)tetraselenafulvalene. Around 70 K (= T FM ), the width of the Bragg reflection increased, and its peak was split into two with decreasing temperature. The direction of splitting was 0.017 a * - 0.010 b * + 0.002 c * in the reciprocal space. At 8.3 K (= T MI ), the discontinuous change in c * was observed, and the peak of the Bragg reflection became single again, but remained broad. In the temperature region of T FM > T > T MI , it is considered that the system has a heterogeneous structure, and the coexistence of the high- and low-temperature phases below T FM is presumably related to the anomalous behavior of dielectric constant in the metallic phase. The size of regions/domains was estimated to be about 0.4 µm.

Microwave conductivities and dielectric constants along the c axis at 44.5 GHz in a π-d correlated metal λ-(BEDT-TSF) 2 FeCl 4 have been measured by a cavity perturbation technique as a function of temperature and magnetic field. In the anomalous metallic states at 8.3 K(= T MI ) < T < 70 K(= T FM ), the microwave conductivity is much lower than the dc conductivity, while the dielectric constant is enhanced to the order of 10 3 , taking a broad maximum around 30 K. From the results of 'H-NMR and recent X-ray diffraction measurements, it is expected that dielectric domains or stripes might emerge heterogeneously in the metallic background. Drastic changes have been observed in the microwave response below T MI which shifts to lower temperatures by external magnetic fields. The anomalous metallic state is found to recover in the reentrant metallic states under magnetic fields higher than the critical field for the reentrant transition.

Extending previous 77 Se NMR studies [J. Phys. Soc. Jpn. 72 (2003) 483], the microscopic magnetic properties of superconducting (\(T_{\text{C}}\cong 5{\mbox{--}}6\) K) λ-(BETS) 2 GaCl 4 [BETS = bis(ethylenedithio)tetraselenafulvalene] have been investigated by 1 H NMR in the normal state between 7.1 and 140 K on randomly oriented single crystals. Contrary to almost T -independent 1/( 77 T 1 T ) of the 77 Se NMR, 1/( 1 T 1 T ) of the 1 H NMR shows a significant increase below about 25 K. This quite contrasting low- T behavior in 1/( T 1 T ) between 77 Se and 1 H is shown to be explained consistently in terms of the development of antiferromagnetic spin fluctuations of π-electrons, which has already been indicated by the 77 Se NMR as a significant low- T decrease in the intrinsic uniform susceptibility χ q =0 ( T ) and no concomitant decrease in 1/( 77 T 1 T ). In the explanation, it is pointed out that the inter-atomic dipolar interaction with the extended spin polarization of the HOMO plays an important r...

We have studied magnetic field effects on the nonlinear electrical transport associated with a negative resistance and switching phenomena in an antiferromagnetic insulating (AFI) ground state of the title π– d coupled conductor below the metal-to-insulator transition temperature T MI =8.3 K. The overall characteristics of current density ( J ) versus electric field ( E ) are well reproduced by an empirical formula with a current-density-dependent conductivity proportional to J n ; if n >1, a negative resistance effect (d J /d E 0) appears. With increasing magnetic field, there appears a crossover from n >1 to n

The microscopic magnetic properties of superconducting (\(T_{\text{C}}\cong 6\) K) λ-(BETS) 2 GaCl 4 (BETS = bis(ethylenedithio)tetraselenafulvalene) have been investigated by 77 Se NMR in the normal state between 7.1 and 100 K on randomly oriented single crystals with κ-(BETS) 2 GaCl 4 as a reference compound. From the T -dependences of the Knight shift and the linewidth, the intrinsic uniform susceptibility χ q =0 ( T ) has been found to decrease with decreasing T below 30 K for λ-(BETS) 2 GaCl 4 . Nevertheless, 1/( T 1 T ) does not show any corresponding decrease but is constant down to the lowest T , which indicates increasing contributions with decreasing T from antiferromagnetic spin fluctuations. The Knight shift and 1/( T 1 T ) have been analyzed quantitatively and the enhancement factor K (α)>1 is deduced in the low- T limit. On the basis of these results, the development of antiferromagnetic spin fluctuations of π-electrons at low T is concluded for λ-(BETS) 2 GaCl 4 .

By the reaction of a new donor molecule, ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide (1) with FeBr3, GaBr3 or FeCl3 in CH3CN/CS2 charge transfer (CT) salts of 1 with counteranions of FeBr4−, GaBr4− or FeCl4− (12·FeBr4, 12·GaBr4 and 12·FeCl4) as plate crystals were obtained. Their crystal structures are apparently similar to each other, in which 1 molecules are dimerized in the parallel direction of their molecular long axes, and the dimers are stacked with changing the direction of the molecular long axes alternately to form a one- dimensional column. The counteranions intervene between the 1-stacked columns and are aligned in a zigzag manner. The room-temperature electrical conductivities of 12·FeBr4 and 12·GaBr4 are fairly high (10–15 S cm−1), but a small value (0.8 S cm−1) is obtained for 12·FeCl4. For all CT salts, temperature dependences of electrical conductivity are semiconducting in spite of very small activation energies (30–90 meV). Based on the comparison between their electrical conducting and magnetic properties, it is suggested that the d spins of FeBr4− or FeCl4− ions exert almost no influence on the π conducting electrons in the 1-stacked column.

We have studied the vortex phase diagram of the organic superconductor κ -(BEDT-TTF) 2 Cu[N(CN) 2 Br], which has layer structure like high temperature superconductors, by means of in- and out-of plane resistivity, ρ ∥ and ρ ⊥ , and DC magnetization measurements as a function of temperature in magnetic fields H perpendicular to the conducting plane. A sharp drop of resistance is observed for the first time at a characteristic temperature T m both in ρ ∥ and ρ ⊥ . Around this temperature, the DC magnetization shows a discontinuous step. These results strongly suggest the existence of the first-order phase transition of vortex system, which can be ascribed to either the vortex lattice melting, or the simultaneous melting and decoupling.

The temperature dependence of the microwave conductivity σ 1 and dielectric constant e 1 has been measured on λ-(BEDT-TSF) 2 FeCl 4 by a cavity perturbation method at 16.3 GHz, employing the TE 011 resonant mode. In spite of the highly metallic state above the metal-to-insulator (MI) transition at T MI = 8.3 K, a novel ferroelectric-like response is observed in e 1 c along c at high temperatures from T MI to T FM = 70 K, which is enhanced to the order of 10 3 just above T MI . Then a transition from a ferroelectric-like to paraelectric-like state with e 1 c ∼ 45 takes part in the MI transition. In contrast to the dc conductivity, σ 1 c becomes much more conductive as considered by a collective mode. The ferroelectric-like response is associated with the dynamical response of the charge degrees of freedom in the π electronic system. An absence of these dielectric and thermodynamical anomalies in the nonmagnetic Ga analogue indicates the importance of the π– d interaction for the ferroelectric-like state as...

The acoustic de Haas-van Alphen (dHvA) effect and temperature dependence of the transverse mode ( C 11 - C 12 )/2 have been measured in a layered Perovskite superconductor Sr 2 RuO 4 with T c * = 1...

To study the magnetic ground state in the title compound of a quasi two-dimensional charge transfer salt containing Fe 3+ ( S = 5/2) paramagnetic ions, we have measured the magnetic torque at 0.4 K ≤ T ≤4 K and H ≤14 T using a capacitive cantilever torque meter. The torque and magnetization data above 1 K are well scaled by the Brillouin plot with a Weiss temperature of -0.8 K. From theoretical analysis for a uniaxial antiferromagnet, anomalous torque curves below 1 K reveal that an antiferromagnetic ordering with its easy axis perpendicular to the conducting a c -plane occurs between 0.5 K and 1 K. This antiferromagnetic order coexists with the metallic state of π-electrons, indicating quite weak π- d interaction.

We report high-resolution measurements of the coefficient of thermal expansion, $\ensuremath{\alpha}{=l}^{\ensuremath{-}1}\ifmmode\times\else\texttimes\fi{}(\ensuremath{\partial}l/\ensuremath{\partial}T),$ on single crystals of the organic superconductors ${\ensuremath{\beta}}^{\ensuremath{''}}\ensuremath{-}{(\mathrm{ET})}_{2}{\mathrm{SF}}_{5}{\mathrm{CH}}_{2}{\mathrm{CF}}_{2}{\mathrm{SO}}_{3}$ and $\ensuremath{\kappa}\ensuremath{-}{(\mathrm{ET})}_{2}\mathrm{Cu}(\mathrm{NCS}{)}_{2}.$ For both salts we find large and highly anisotropic phase-transition anomalies at ${T}_{c}.$ Combining these data with literature results on the specific heat via the Ehrenfest relation, the uniaxial pressure coefficients of ${T}_{c}$ can be determined. Most remarkably, a strikingly similar in-plane vs out-of-plane anisotropy is found for both compounds: the strong suppression of ${T}_{c}$ observed in hydrostatic-pressure experiments is dominated by a huge negative uniaxial stress effect perpendicular to the conducting planes. Therefore we expect that an increase of ${T}_{c}$ in this class of superconductors can be obtained by enlarging the distance between the conducting layers. Application of magnetic fields perpendicular to the planes for the ${\ensuremath{\beta}}^{\ensuremath{''}}\ensuremath{-}{(\mathrm{ET})}_{2}{\mathrm{SF}}_{5}{\mathrm{CH}}_{2}{\mathrm{CF}}_{2}{\mathrm{SO}}_{3}$ salt were found to result in pronounced superconducting fluctuation effects and scaling behavior in $\ensuremath{\alpha}(T,B).$ Owing to the pronounced phase-transition anomalies in $\ensuremath{\alpha}(T,B)$ at ${T}_{c},$ our measurements allow for an accurate determination of the upper critical fields. We find ${B}_{{c}_{2}}^{\ensuremath{\perp}}(0)=(1.4\ifmmode\pm\else\textpm\fi{}0.2) \mathrm{T}$ and ${B}_{{c}_{2}}^{\ensuremath{\Vert}}(0)=(10.4\ifmmode\pm\else\textpm\fi{}0.5) \mathrm{T}$ for fields perpendicular and parallel to the conducting planes, respectively.

The range of thermal fluctuations in ‘classical’ bulk superconductors is extremely small and especially in low-fields hardly experimentally accessible. With a new type of calorimeter we were able to detect a tiny lambda anomaly in the specific-heat of the superconductor Nb3Sn within a narrow temperature range around the Hc2 line. We show that the evolution of the anomaly as a function of magnetic field follows scaling laws expected in the presence of critical thermal fluctuations.

Single crystals of a new compound Nb5Sn2Ga were obtained by the flux method using molten tin as a solvent. The crystal structure represents a tetragonal symmetry, space group D4h18I4/mcm, ordered W5Si3-type structure. Lattice parameters are a=1.0586(2) nm and c=0.5177(1) nm. According to XPS study, the peaks of Nb, Sn and Ga 3dXP spectra negatively shift when the three elements of Nb, Sn and Ga form the compound of Nb5Sn2Ga. The compound shows superconductivity at Tc=1.75 K and ΔTc=140 mK. The residual resistivity ratio, RRR=ρ (293 K)/ρ (4.2 K), is 12. The Micro-Vickers hardness (MVH) value for the (100) or (110) face is 8.9–8.5 GPa, and for the (001) face is 10.1–9.1 GPa. Oxidation of the Nb5Sn2Ga starts at 562°C. Weight gain of the compound heated up to 1200°C in air is 37.3%. Final oxidation product contains NbO2, Nb2O5, Nb12O29, SnO2 and Ga2O3.

Ultrasound velocity measurements based on a phase comparison method for four different modes have been done on a copper-free layered perovskite superconductor Sr 2 RuO 4 with T c = 1.2 K. Anomalous softening is observed in the longitudinal C 11 and C 33 modes below 108 K, which is attributed to the coupling of the electronic states to the strain with Γ 1 representation in the tetragonal point group D 4h . The discontinuous change of the slope in C 11 and C 33 at T c is basically explained by the second-order strain dependence of T c , ∂ 2 T c /∂e 2 uk . From the initial slope of the upper critical field H c2 , the anisotropy ratio in the coherence length is found to be 28, in agreement with previous ac susceptibility measurements. Acoustic de Haas-van Alphen oscillations for the cylindrical α-Fermi surface with 3.2 m 0 are observed in C 33 as a function of the magnetic field applied perpendicular to the Q2D conducting plane. The area coefficient is evaluated to be ∣Λ zz ∣ = 20±5 from the Kataoka-Goto mode...

We have studied the complex conductivity in superconducting and normal metallic states of CeRu 2 by the surface impedance measurements at millimeter-wave frequency of 45.4 GHz. The temperature dependence of the complex conductivity below T c = 6.2 K exhibits the characteristic behaviors as seen in a conventional superconductor. The coherence peak observed in the real part σ 1 provides a strong evidence for a conventional s -wave superconductivity as well as the previous NQR measurements. The temperature dependence of the penetration depth evaluated from the surface reactance at low temperatures has revealed the ratio of 2 Δ(0)/ k B T c = 4.4. The strong-coupling theories suggest the electron-phonon coupling strength with λ ep < 2. These results indicate that CeRu 2 is an intermediate strong-coupling superconductor in a clean limit.

Longitudinal sound velocity measurements propagating along the interlayer direction have been performed at 53.4 MHz by a phase comparison method on a quasi-two-dimensional (Q2D) organic superconductor α-(BEDT-TTF) 2 NH 4 Hg(SCN) 4 with T c = 1 K. Temperature dependence of the sound velocity shows anomalies around 20 K and 60 K. The acoustic de Haas-van Alphen (dHvA) effects are observed below 1.8 K for the first time in these organic metals. The quantum oscillations originate from the α-Fermi surface (FS) of a weakly warped cylindrical shape. According to the theoretical formulations by Kataoka and Goto for an acoustic dHvA effect, the absolute area coefficient | Λ L | is estimated to be about 3.5. The multiband term Λ L m is concluded to dominantly contribute to | Λ L |.

The 1:2 mixed tetramethylammonium (NMe 4 + ) ( 1 ) and tetramethylphosphonium (PMe 4 + ) salts ( 2 ) of 2,5-dimethyltetracyano-quinodimethane (DMTCNQ) and its radical anion (DMTCNQ −⋅ ) were prepared, which exhibited both ferromagnetic behavior and high electrical conductivity at room temperature. The crystal structure of 2 showed a composition of two different DMTCNQ/DMTCNQ −⋅ (1:1) and DMTCNQ −⋅ columns, which have significant contact with each other.

The neutral bis(dialkylthiotetrathiafulvalenyldithiolato)copper complexes, Cu(R2C6S8)2 (R=Me 1a, Et 1b, R2=–CH2CH2– 1c) were synthesized by the reaction of bis(tetramethylammonium or tetraethylammonium) bis(dialkylthiotetrathiafulvalenyldithiolato)zincate complexes with CuCl2 in DMF, followed by oxidation with iodine. The room-temperature electrical conductivities were 7.8×10–2 , 5.0×10–4 and 3.7 S cm–1 for compressed pellets of 1a, 1b and 1c, respectively. Magnetic susceptibility measurements showed that the remaining spin on the copper atoms is very small for these complexes as a result of large intramolecular electron transfer from CuII atom to the tetrathiafulvalenyl radical cation ligands.

Recent developments in the field of π-conjugated polymers have led to considerable improvements in the performance of solution-processed organic light-emitting devices (OLEDs). However, further improving efficiency is still required to compete with other traditional light sources. Here we demonstrate efficient solution-processed multilayer OLEDs using small molecules. On the basis of estimates from a solvent resistance test of small host molecules, we demonstrate that covalent dimerization or trimerization instead of polymerization can afford conventional small host molecules sufficient resistance to alcohols used for processing upper layers. This allows us to construct multilayer OLEDs through subsequent solution-processing steps, achieving record-high power efficiencies of 36, 52 and 34 lm W(-1) at 100 cd m(-2) for solution-processed blue, green and white OLEDs, respectively, with stable electroluminescence spectra under varying current density. We also show that the composition at the resulting interface of solution-processed layers is a critical factor in determining device performance.

We have made a high-resolution photoemission study of quasi-two-dimensional organic conductors BEDT-TTF salts which have various ground states, namely, antiferromagnetic insulator {kappa}-(ET-d{sub 8}){sub 2}Cu[N(CN){sub 2}]Clthinsp, paramagnetic metal {alpha}-(ET){sub 2}KHg(SCN){sub 4}, and superconductors {kappa}-(ET){sub 2}Cu(NCS){sub 2} and {kappa} -(ET){sub 2}Cu[N(CN){sub 2}]Br, where ET denotes BEDT-TTF or bisethylenedithio-tetrathiafulvalene. In all the spectra, the photoemission intensity is suppressed near the Fermi level (E{sub F}), especially for the {kappa}-phase salts, although we have clearly observed a finite E{sub F} intensity for {alpha}-(ET){sub 2}KHg(SCN){sub 4}. Hartree-Fock band-structure calculations for the paramagnetic metallic and antiferromagnetic insulating states qualitatively explain the spectra of {alpha}-(ET){sub 2}KHg(SCN){sub 4} and {kappa}-(ET-d{sub 8}){sub 2}Cu[N(CN){sub 2}]Cl, respectively, while those of {kappa}-(ET){sub 2}Cu(NCS){sub 2} and {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br strongly deviate from the calculations for the corresponding ground states. These observations imply that, among the metallic compounds, electrons are more strongly correlated in the {kappa}-phase salts than in {alpha}-(ET){sub 2}KHg(SCN){sub 4}. It is shown that long-range electron correlation is quite important to explain the strong deviation of the spectra from the band-structure calculation. The spectra of the {kappa}-phase salts exhibit a remarkable similarity between the metallic (superconducting) and insulating phases across the chemical pressure-induced phase transition. We have also observed unusual temperature dependence ofmore » the spectra for {kappa}-(ET){sub 2}Cu(NCS){sub 2}, {alpha}-(ET){sub 2}KHg(SCN){sub 4}, and {kappa}-(ET-d{sub 8}){sub 2}Cu[N(CN){sub 2}]Cl. {copyright} {ital 1997} {ital The American Physical Society}« less

Ferromagnetic behavior at room temperature was observed in the tetramethylammonium (NMe4+) and cesium (Cs+) salts of tetracyanoquinodimethane (TCNQ) and its radical anion (TCNQ−) in a molecular ratio of 1:2. The saturation magnetizations and coercive forces are 0.79 emu/mol and ca. 300 Oe for (NMe4+·T·CNQ−)·l/2TCNQ, and 1.46 emu/mol and ca. 100 Oe for (Cs+·TCNQ−)·1/2TCNQ, respectively. In contrast, the 1:1 TCNQ/ TCNQ− mixed tetraethyammonium(NEt4+) salt, (NEt4+·TCNQ−)·TCNQ, exhibited no ferromagnetic behavior at room temperature and also at lower temperatures.

The structure of a plate crystal of ((PMq+. TCNQF4 −) 1/2TCNQF4) was analyzed and very similar to that of the corresponding NMe4 + salt. However, significant difference was recognized between the two crystals in the structures of TCNQF4 and TCNQF4 − molecules, and especially in the contacts between the two TCNQF4 − molecules in dimerization and between the TCNQF4 and TCNQF4 − molecules. The change in both molecular structure and contact as above was also observed at a lowering temperature. The magnitude in change was larger in the NMe4+ salt than in the PMe4 + salt. However, the change exerted no special influence on the elctrical conducting and magnetic properties.

Hall effect measurements in the vortex state of the quasi two-dimensional (Q2D) organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 are reported. The sign of the Hall conductivity changes with field and temperature in the vortex state. The Hall conductivity is described as the sum of the two terms resulting from the quasiparticle (∝ H) and the vortex motion (∝ 1/H). The sign of the latter term depends on the current direction in Q2D plane. The behavior can be explained by the anisotropic motion of the charged vortex in the anisotropic Q2D plane.

Magnetic torque of the single crystal of a layered superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br has been measured as a function of field direction with respect to the b-axis under several magnetic fields H up to 8 kOe in the temperature range from 1.5 to 20 K. Smaller value of the anisotropy parameter γ = 180 is obtained for Cu[N(CN)2]Br salt than our previous report γ = 350 for κ-(BEDT-TTF)2Cu(NCS)2. The irreversible region in H — T phase diagram for Cu[N(CN)2]Br salt with smaller γ is larger than that for Cu(NCS)2 salt. A sharp cusp due to the intrinsic pinning is found near H∥ac-plane as in the case of our previous report on other layered superconductors.

Magnetic phase diagram of a quasi-two-dimensional organic conductor \ensuremath{\alpha}-(BEDT-TTF${)}_{2}$KHg(SCN${)}_{4}$ is revisited from a viewpoint of magnetic torque measurements in high fields up to 30 T. A phase boundary that is interpreted as a metal-spin density wave (SDW) phase transition is found by using torque measurements. It is shown that this phase boundary is clearly distinguished from so-called kink transition of the magnetoresistance. We demonstrate that the transition temperature defined by the midpoint of the broad phase transition is almost independent on magnetic field up to 23 T. Onset temperature of the transition shifts from about 8 K at H=0 T to higher temperatures with increasing of a magnetic field, and tends to be saturated. The onset line of this transition follows well the theoretical expectation that SDW has to be stabilized by a magnetic field. This allows us to estimate such important band parameters of the quasi-one-dimensional section of the Fermi surface as an effective mass, ${\mathit{m}}^{1\mathrm{D}}$\ensuremath{\simeq}(0.5\ifmmode\pm\else\textpm\fi{}0.1)${\mathit{m}}_{0}$, and an upper limit of an imperfect nesting bandwidth ${\mathit{t}}_{\mathit{c}}$\ensuremath{'}\ensuremath{\simeq}(10 \ifmmode\pm\else\textpm\fi{}1) K. The other phase boundaries determined by the position of the kink and hysteresis properties of the magnetoresistance are interpreted as subphases inside the SDW phase. Inside the SDW phase, we find an additional phase boundary at the temperature-independent field of 23 T, which corresponds to the appearance of de Haas--van Alphen oscillations on a magnetic torque curve. At the 23 T boundary, both the effective mass, m*, and the Dingle temperature, ${\mathit{T}}_{\mathit{D}}$, change their values from m*=(1.67 \ifmmode\pm\else\textpm\fi{} 0.05) ${\mathit{m}}_{0}$ and ${\mathit{T}}_{\mathit{D}}$=3.7--4.0 K in low magnetic field region to (1.95 \ifmmode\pm\else\textpm\fi{} 0.05) ${\mathit{m}}_{0}$ and 2.5--2.8 K in high field region. The latter phenomenon is discussed in terms of a reconstruction of the Fermi surface due to the SDW formation. Hysteresis of the magnetoresistance observed in one of the subphases inside the SDW phase is studied in detail by measuring both the temperature and the magnetic field dependences. \textcopyright{} 1996 The American Physical Society.

We report on the Hall effect measurements of the quasi two-dimensional organic superconductor κ-(BEDT-TTF) 2 Cu(NCS) 2 . A sign reversal phenomenon of the Hall resistivity is found in the mixed state. The Hall conductivity changes monotonically with field and temperature in contrast to the peak structure observed in the Hall resistivity. In low fields, the Hall conductivity diverges to infinity as −1/(H-H ∗ ) , where H ∗ is characteristic field in which the resistivity becomes zero. The phase diagram is proposed from these results.

We have synthesized a new organic conductor α-(BEDT-TTF) 2 KHg(SeCN) 4 which is found to be isostructural with a family of α-(BEDT-TTF) 2 MHg(SCN) 4 with M=K, Tl, Rb and NH 4 , where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene. In contrast to superconducting (M=NH 4 ) or antiferromagnetic (M=K, Tl, Rb) salts, the title compound remains a normal metal in the same way as α-(BEDT-TTF) 2 TlHg(SeCN) 4 . The magnetoresistance and the Shubnikov-de Haas (SdH) effect have been measured at temperatures down to 0.5K and magnetic fields up to 23T. The SdH frequency of 670T, the effective mass of 2.0 m 0 , and the Dingle temperature of 1.6K are obtained in fields perpendicular to the conductive a - c plane. The magnetic field direction dependence of the frequency shows that the observed Fermi surface has a cylindrical shape. The temperature and the field dependence of the SdH oscillation amplitude are well explained by the standard Lifshitz-Kosevich formulation, indicating that the effective mass is essentially ...

The response of the superconducting charge carriers to an applied magnetic field has been probed in a number of organic superconductors using μSR. Systematic studies have been made of the in-plane superconducting penetration depth λ in superconductors based on the ET and BETS molecules. These studies have revealed a strong correlation between λ and T c . This type of correlation was first noted in high T c cuprates by Uemura et al who found a linear relation between T c and λ -2 . In the case of organic superconductors, however, we find that the overall correlation is better described as T c λ -3 . Understanding this characteristic trend should provide some important clues about the nature of the superconductivity in the organic superconductors; several possible models are considered here for describing this behaviour. It is concluded that models in which the superconducting carrier concentration is tied to the nominal band filling are inconsistent with the observed scaling behaviour.