田島 裕之

A ternary type-I Si clathrate K8Ga8Si38 has been revealed to be an indirect band gap semiconducting material with an energy gap (E-g) of approximately 0.10 eV, which is much smaller than the calculated E-g value that is 0.15 eV wider than E-g of elemental Si with the diamond-type structure.

The photocurrent responses were investigated for the biomolecular bulk-hetero junction of chlorophyll a (Chl-a) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-1-phenyl-(6,6)C-61 (PCBM) in the temperature range between 300 K and 1.5 K under the magnetic field up to 8 T. The chopped-light photocurrent decreases on lowering the temperature. Below 10 K, photocurrent decrease was observed under the applied magnetic field. Decay of the photocurrent observed at 10 K was ascribed to the formation of the charged trap under light irradiation. The magnetic field effect (MFE) observed in this device was found to be very similar to that observed in P3HT:PCBM bulk-hetero junction at low temperatures.

A series of pi-conjugated alternating copolymers consisting of Th-ITN-Th and p-C(6)H(2)(OR)(2) units were synthesized. XRD indicated that the copolymers assume an interdigitation packing mode, and UV-Vis spectra revealed a strong tendency for self-assembly. Upon molecular assembly of the copolymer, the UV-Vis absorption shifted by about 100 nm to a longer wavelength from that of the single molecule. The copolymers underwent electrochemical oxidation (or p-doping) and reduction (or n-doping) at 0.2 and -2.0 V versus Ag(+)/Ag, respectively. A p-doped copolymer film showed an electrical conductivity of 182 S.cm(-1), and the temperature dependence of electrical conductivity was measured. The copolymer showed piezochromism and served as a p-channel material for a field-effect transistor.

Magnetic torque measurements of TPP[Fe(Pc)Br-2](2) are reported The torque curves for the magnetic field rotated within the ac plane exhibit a two-fold symmetry The temperature dependences of the torque amplitudes divided by the square of the field strength (tau(phi-45)/B-2) exhibit a drastic field dependence below 12K This field dependence is attributable to the fluctuation in the spontaneous magnetization that appears below 4 5 K The torque curves for the field rotated within the ab plane exhibit four-fold symmetry The curves are sinusoidal above 18K and exhibit saw-toothed shapes below similar to 12 K and complicated shapes below 8K. The complicated shapes suggest that both d-electrons and it-electrons form a magnetic order below 8K (C) 2009 Elsevier B V All rights reserved

A novel Fe(III) spin crossover (SCO) complex with a linear I(3) anion [Fe(qsal)(2)]I(3) 1 [qsalH=N-(8-quinolyl)-salicylaldimine] was prepared and characterized by the magnetic susceptibilities and crystal structures 1 exhibited a gradual SCO conversion (T(SCO)= ca 240 K) The crystal structural analyses for 1 at 50 and 293 K revealed that the two-dimensional (2D) network was constructed by intermolecular pi-pi interactions between pi-ligands of an Fe(III) cation Since the related complex [Fe(qsal)(2)]NCS 2 was known to show a cooperative SCO transition the crystal structure of 2 at 293 K was also determined 2 possessed 2D SCO cation arrangement similar to 1 whereas potential pi-pi interactions between 2D networks in 2 existed The dimensionality of intermolecular interactions was closely related to SCO behaviors and pressure effects on SCO compounds (C) 2009 Elsevier B V All rights reserved

Magnetoresistance (MR) and magnetic torque measurements are performed for a magnetic organic conductor TPP[Fe(Pc)(CN)(2)](2). The results suggest that the large negative MR is associated with a magnetic transition. This magnetic transition is considered as a metamagnetic transition of the localized Fe moments, and the MR effect is qualitatively explained by an analogy with the double exchange interaction system.

The photocurrent responses were investigated for the bulk-hetero-junction of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-1-phenyl-(6,6)C(61) (PCBM) (1), and the single-active-layer junction of (5,10,15,20-tetraphenyl porphyrinato)zinc (II) (Zn(TPP)) (2), in the temperature range between 300 K and 1.5 K under the magnetic field up to 8 T. Magnetic field effect (MFE) of the photocurrent was observed in both devices. In the device (1), MFE at low temperatures was small for the continuous light illumination, but remarkable for the chopped-light illumination. An experiment of photoinduced charge extraction by linearly increasing voltage (photo-CELIV) revealed a drastic increase in the lifetime for trapped carriers under applied magnetic field. In the device (2), the photocurrent decrease under magnetic field was observed both for the continuous-light and the chopped-light illumination. (C) 2009 Elsevier B.V. All rights reserved.

Electrochemical oxidation of [M(III)(Pc)(CN)(2)](-) (M = Co and Fe, Pc = phthalocyaninato) and peri-xanthenoxanthene (PXX) in acetonitrile yields partially oxidized salts of [PXX](2)[M(Pc)(CN)(2)]center dot CH(3)CN. In the crystal, the Pc ring is formally oxidized by 0.5 e and forms a two-dimensional double-sheet layer. These crystals show semiconducting behavior with small activation energy under ambient pressure, but show metallic behavior under high pressures. When M - Co, the metallic behavior is maintained down to 5 K. On the other hand, in the pi-d system with M = Fe, the metallic behavior is disrupted by a steep increase in the resistivity at low temperatures. In this high resistivity state, negative differential resistance appears in the measurements of current-voltage characteristics, suggesting the development of charge disproportionation due to the pi-d interaction. The magnetic susceptibility for M = Fe reflects anisotropic molecular magnetism of the Fe(Pc)(CN)(2) unit, and shows an anomaly due to antiferromagnetic interaction between the Fe d-spins. The increase in the resistivity at low temperature under high pressures is suppressed by the application of a magnetic field. The magnitude of the negative magnetoresistance effect is extremely large; -99.8% was recorded at a field of 15 T at 3 K under 12 kbar.

A supramolecular copper complex, [Cu(I)Cl0.2Br1.3(pyra-TTF)(0.5+)] (4) (pyra-TTF = pyrazino-tetrathiafulvalene), was synthesized by a coordination of the assembled oxidized donor ligands as the conduction paths and the disordered mixed halide anion ligands. The one-dimensional complex 4 reveals the metallic behavior down to 190 K with a resistivity minimum at 250 K and transforms to semiconducting behavior by the CDW (charge density wave) transition at 190 K with the doubling of the donor stacking c-axis. However, the complete singlet state is prohibited by the rigid 1D copper halide framework, [CuCl0.2Br1.3](n).

The photocurrent responses of organic MIM junctions were investigated for light chopped at various frequencies in the temperature range between 300 K and 1.5 K. The responses to different chopping frequencies exhibited different temperature dependences. A light-chopped photocurrent markedly decreased under magnetic fields at low temperatures. An experiment of photoinduced charge extraction by linearly increasing voltage (photo-CELIV) was performed at 1.4 K to reveal the origin of this phenomenon. A drastic increase in the lifetime was observed for trapped carriers under applied magnetic field. (C) 2009 Elsevier B.V. All rights reserved.

We have successfully obtained spin-coated films of unsubstituted planar phthalocyanines (free-base and copper phthalocyanine) from trifluoroacetic acid and chlorobenzene mixed solutions for the first time. The pre-annealed films did not consist of pure phthalocyanines; these films contained the solvent molecules. However, the residual solvent molecules could be removed by annealing at 425 K for 2 h in vacuum. This technique is useful for fabricating unsubstituted planar phthalocyanine thin films. (C) 2009 Elsevier B.V. All rights reserved.

The charge transport properties of a partially oxidized salt composed of Co(Pc)(CN)(2) units with a typical one-dimensional electronic system have been suggested to be determined by charge disproportionation. The current-voltage (I-V) characteristics show nonlinear behavior at low temperature, which is suppressed by applying pressure. The observed nonlinearity is considered to result from the electric-field-induced delocalization of carriers in the charge disproportionation state. In the isomorphous magnetic Fe(Pc)(CN)(2) system, the nonlinear behavior is observed at higher temperatures, suggesting that charge disproportionation is more developed in a system with local moments. The threshold voltage of negative differential resistance decreases when an external magnetic field is applied, confirming that the localization of charge carriers is released by magnetic field application.

Self-assembly of polythiophenes with -C CR (R = alkyl, phenyl, etc.) side chains has been investigated. Seven new polymers consisting of head-to-head and tail-to-tail 2,2'-bithiophenes with -C CR side chains were synthesized. The new polymers include alternating copolymers between bithiophenes with -C C-alkyl side chains and thiophene and those between bithiophenes with -C C-alkyl side chains and 2,2'-bithiophene. The polythiophene main chain is considered to be coplanar because of the absence of steric repulsion between the main chain and the -C CR side chain. Single-crystal X-ray crystallography and DFT calculations indicated that the head-to-head- and tail-to-tail-2,2'-bithiophenes with -C CR side chains were coplanar. The polythiophenes with -C CR side chains showed a strong tendency to self-assemble, and assumed edge-on alignment and side-on alignment on the surface of substrates. Self-assembly caused a decrease in the pi-pi* transition energy of the polymers by 0.3-0.4eV. A copolymer of thiophene and dialkoxy-p-phenylene showed analogous self-assembly. The polythiophenes with -C CR side chains showed piezochromism, with a decrease in the pi-pi* transition energy by about 0.2eV at 10GPa. Head-to-head-P3(C C-Dec)Th with a -C C-decyl side chain gave a larger optical third-order nonlinear susceptibility chi((3)) than regio-regular poly(3-hexylthiophene)s.

Magnetic torque (3≤T≤46 K), dc magnetic susceptibility (2≤T≤300 K), and ac magnetic susceptibility (2≤T≤30 K) are reported for PTMA0.5[Fe(Pc)(CN)2]･CH3CN. The torque curves exhibit a sinusoidal line shape for temperatures above 6 K. This result as well as the temperature dependence of the dc magnetic susceptibility above 13 K was analyzed by employing an anisotropic Heisenberg model in one dimension. The compound exhibits spontaneous magnetization below 6 K. The torque measurements at 3 K revealed that the direction of this spontaneous magnetization is parallel to the easy axis of the mother antiferromagnetism. The ac susceptibility measurements demonstrated the fluctuation of the spontaneous magnetization up to 13 K. A model of charge-ordered ferrimagnetism is proposed in order to explain these results. This model explains the spontaneous magnetization which commonly appears in conducting salts of [Fe(Pc)(CN)2] and their derivatives.

We have carried out an experimental study to reveal the dielectric function of SmH(x)(x=2.28,2.42,2.56,2.57) films based on room-temperature reflectivity for photon energies ranging from 0.05 to 6.5 eV. The derivation of the dielectric functions has been carried out using model dielectric functions as well as Kramers-Kronig analysis. It is inferred from our analysis that when the H/Sm value is increased from 2.28 to 2.57, (i) the interband transition band located in the ultraviolet region shows a redshift of about 1 eV, (ii) the relatively weak transition band located in the near-infrared region shows a reduction in intensity, and (iii) the unperturbed plasma frequency of free carriers decreases slightly. The behaviors (i), (ii), and (iii) caused by the H/Sm value change are thoroughly approximately the same as those observed for YH(x), suggesting that these trends are characteristic of H-M systems showing a metal-insulator transition. It was also confirmed from our structural analysis that these changes in the dielectric function are achieved without a change in the lattice constant. The origin of this constancy in the lattice constant in our samples with different H/Sm values is discussed by assessing the T- and O-site hydrogen concentrations. The hydrogen incorporation effect is also observed in the magnitude of the unperturbed plasma frequency, about 1.7 eV, which is unexpectedly small compared to conventional metals. This characteristic can possibly be attributed to mass enhancement of mobile carriers; we obtained an effective mass of about 10m(0) (where m(0) is the free electron mass) when the carrier density estimated from the Hall coefficient value is used.

A series of one-dimensional conductors, TPP[Fe-III(Pc)L-2](2) with L CN, Cl, and Br, have been prepared. These compounds show giant negative magnetoresistance due to the interaction between conduction pi-electrons and localized Fe-centered d-spins, but the magnitude is found to vary based on the axial ligand, suggesting that the strength of the pi-d interactions is sensitively influenced by the axial substituent. The magnetic susceptibility also shows the difference in the magnetic interactions by the axial substituent. The ab initio calculation of the isolated molecules has revealed that the Jahn-Teller effect in this system induces splitting of d(xz) and d(yz) orbitals, and that the energy shift of the d-orbital accommodating an unpaired electron is varied by the axial substituent. The axial-ligand dependence of the intramolecular pi-d interaction is found to correlate with the magnitude of the magnetoresistance.

To investigate the relationship between molecular orientation and current voltage (J-V) characteristics, molecular orientation and J-V characteristics have been simultaneously measured in some indium tin oxide (ITO)/X/Al structures. X were thin films fabricated from poly(3-hexylthiophene) (P3HT), coumarin6 dispersed in poly(N-vinylcarvazole), or biomolecular hemin (Hm). The results have shown that the orientation change of the P3HT chain causes a reproducible loop of the J-V characteristics in P3HT thin film, and that the peak observed in the J-V characteristics in Hm is associated with irreversible molecular orientation change. (C) 2008 Elsevier B.V. All rights reserved.

To examine the mechanism of a reproducible on-off switching of light emission from a novel organic electroluminescent (EL) device consisting of a spin crossover complex of [Fe(dPP)(2)](BF(4))(2) (dpp=2,6-di (pyrazol-1-yl)pyridine) and chlorophyll a, we have investigated the EL properties of an ITO/chlorophyll a: [Fe(dPP)(2)](BF(4))(2)/Al device. The comparison with a reference device not containing [Fe(dpp)(2)](BF(4))(2) revealed that the introduction of [Fe(dpp)(2)](BF(4))(2) results in small threshold voltage and large external quantum efficiency. Moreover, the EL spectra in the low-temperature region, where [Fe(dpp)(2)](BF(4))(2) is in the low-spin state, showed the emission from the ITO electrode, suggesting that injected electrons pass through the active layer via [Fe(dPP)(2)](BF(4))(2). (c) 2008 Elsevier B.V. All rights reserved.

Magnetic torque and heat capacity measurements on TPP[Fe(Pc)(CN)2]2 are reported. The torque curves for the magnetic field rotated within the ab plane have a fourfold symmetry, exhibiting inversions around 13 and 27K. The heat capacity exhibits a broad peak around T=16.5K. By applying the magnetic field along the c axis, the maximum value of the heat capacity is enhanced below 20K. These results, as well as the magnetic susceptibility, were analyzed by employing a numerical calculation based on the anisotropic Heisenberg model in one dimension. The analyses revealed that: (i) the peak in the magnetic-susceptibility data around 25K is due to an antiferromagnetic short-range order (SRO) formation associated with d electrons, and (ii) π electrons fall into an antiferromagnetic state below 13K. The spin-flop field of π electrons is approximately 80kOe at 9K.

New supramolecular copper complexes with pyrazinotetrathiafulvalene (pyra-TTF) as the ligand, [(CUCl2)-Cl-II(pyraTTF)] (1) and (pyra-TTF)(2)[(CU3Cl4)-Cl-I(pyra-TTF)] (2), have been synthesized by- the diffusion method. Complex 1 is a black block crystal with a three-dimensional (3-D) supramolecular network; the linear chain [-(CUCl2)-Cl-II-(pyra-TTF)-](n) extends along the b axis, where the coordinated pyra-TTF donors are stacked in a head-to-tail and ring-over-bond configuration to construct two-dimensional (2-D) sheets, and between the sheets, there are C center dot center dot center dot Cl- or H center dot center dot center dot Cl- contacts. Even though the electron spin resonance (ESR) measurement reveals the nearly Cu-II state, complex 1 is a semiconductor with sigma(RT) = 1.0 X 10(-4) S cm(-1) and E-a = 0.33 eV. The high-frequency conductivity measurement also confirmed the intrinsic slight carrier doping from Cu-II to the pyra-TTF donor. This slight doping enhances not only the real and imaginary dielectric constants but also the antiferromagnetic interaction between Cu-II spins following the 2-D Heisenberg model with 2J = -20 K. In contrast, complex 2 is a very thin black needle. This needle crystal has two crystailographically independent pyra-TTF molecules, which are coordinated and noncoordinated donors. The coordinated donors composed a supramolecular chain [(Cu3Cl4)-Cl-I(pyra-TTF)(0)](n), whereas the noncoordinated donors formed conducting alpha ''-type pyra-TTF+0.5 sheets. This complex is semiconducting with sigma(RT) = 0.1 S cm(-1) and E-a = 0.15 eV. Both complexes 1 and 2 demonstrate that the pyra-TTF molecule works not only as an oxidized donor by Cu-II to construct conducting sheets but also as a ligand coordinated to a Cu cation to form supramolecuar chains.

A novel spin-crossover molecular conductor, [Fe(qnal)(2)] [Pd(dmit)(2)](5)center dot acetone, was prepared and characterized. The crystal structural analyses of both the low- and high-temperature phases revealed that the supramolecular pi-pi interactions between the spin-crossover Fe(qnal)(2) cations as well as the cation contraction play an important role in the uniaxial lattice deformation which will modulate the electrical conductivity of the conducting Pd(dmit)(2) layer.

A film of a spin-crossover complex [Fe(dpp)(2)](BF4)(2) (dpp = 2,6-di(pyrazol-1-yl)pyridine) was embedded into the light-emitting layer of an organic electroluminescent (EL) device with chlorophyll a. While the EL spectrum was observed at 300K, the spectrum could not be observed at 200 K. The temperature dependence of the EL spectra shows the quenching of the emission below 260 K, which is the spin-transition temperature of [Fe(dpp)(2)](BF4)(2). This suggests that the EL quenching accompanied the spin transition.

Head-to-head type poly(3-(1-dodecynyl)thiophene-2,5-diyl), HH-P3(C CDec)Th, formed a well aligned structure in its cast film, and UV-vis absorption peak of the cast film showed a large shift by about I 10 nm to a longer wavelength from that (518 nm) observed in solution. Under high pressure HH-P3(C CDec)Th exhibited clear piezochromism; the UV-vis absorption peak at about 605 nm observed under atmospheric pressure shifted to 672 nm under 10.71 GPa, suggesting an increase in electronic interaction between the polymer molecules under high pressure. The pi-pi* transition energy decreased by 0.028 eV/GPa in the range of 0-5.2 GPa. (c) 2007 Elsevier Ltd. All rights reserved.

Polarized optical reflectance of single crystalline beta-FeSi2 has been investigated up to 3.1 eV for the light polarization of E//a, E//b and E//c. We observed the clear anisotropy in the spectrums of reflectance, refractive index n, extinction coefficient k and dielectric function epsilon, depending on the light polarizations. From the comparison with the experiments and the theoretical calculation, we found that features of those experimental spectrums agrees well with the theoretical ones calculated by the full potential linear augmented plane wave method based on the density functional theory and the dipole approximation. The anisotropy of n was found to be 10-20% between 1 eV and 3.1 eV, while it was small (<similar to 5%) below 1 eV.

We have grown Mg2Si bulk crystals by the vertical Bridgman method using a high-purity Mg (6N-up) source. The grown crystals were single-phase Mg2Si and had well-developed grains (1-5 mm(3)). Lane observations and SEM-EDX observations confirmed that crystalline quality in the grains was single crystal with stoichiometric composition. Electron concentration of the single crystalline specimens grown from 6N-up-Mg was 4.0 x 10(15) cm(-3) at room temperature (RT). This value is more than one order of magnitude lower than that of specimens grown from 4N-Mg [(5-7) x 10(16) cm(-3)]. The Hall mobility of 14,500 cm(2)/Vs was observed at 45 K in the crystals grown from 6N-up-Mg. We also found that Al impurity plays an important role in the crystals grown from a low-purity Mg source. From the optical absorption measurement, we estimated that the indirect energy gap was about 0.66 eV at 300 K and about 0.74 eV at 4 K. (c) 2007 Elsevier B.V. All rights reserved.

Thin film of a spin crossover complex [Fe(dpp)(2)](BF4)(2) (dpp = 2,6-di(pyrazollyl)pyridine) has been fabricated by a spin-coating method. The obtained film exhibits spin transition at around 260 K. The absorption spectra and the electrical resistance change with the spin transition. These phenomena are reproducible through both cooling and heating process.

We have investigated the basic characteristics of mobile carriers in as-deposited thin films of hexagonal-close-packed Y and hydrogenated films of face-centered-cubic YH2+δ. Hall resistance and transverse magnetoresistance measurements were carried out under magnetic fields of up to 1 T at room temperature. The Hall coefficient in YH2+δ showed a minimum value of ∼5× 10-12 m3 /C when the δ value reached ∼-0.1, in accordance with the δ dependence of resistivity reported previously. Quantitative analysis based on the present measurements revealed that YH2+δ is a compensated metal whose carrier density and mobility were determined to be ∼1.4× 1027 (∼1.9× 1027) m-3 and ∼3.5× 10-3 (∼3.1× 10-3) m2 V-1 s-1, respectively, for δ=0.04 (-0.03) for both electrons and holes. These carrier parameters were found to account concurrently for the reflection spectral line shapes observed. The compensation observed in YH2+δ is at variance with a simple criterion used previously [E. Fawcett and W. A. Reed, Phys. Rev. 131, 2463 (1963)]. © 2007 American Institute of Physics.

Hall resistance and transverse magnetoresistance measurements were performed under magnetic fields of up to 5T to reveal the basal characteristics of mobile carriers in near- stoichiometric dihydrides YH2+x (x = -0. 23 and 0.04). Unusually small Hall coefficients, e. g. 9. 0 x 10(-12) m(3)/C for x = -0. 23, were observed, leading us to the tentative conclusion that f. c. c. YH2+x is a compensated metal in which electrons and holes have nearly equal carrier density. In addition, carrier mobility was revealed to be nearly equal for electrons and holes, with a difference of less than 7%. (c) 2006 Elsevier B. V. All rights reserved.

The photocurrent responses of polymer solar cells were investigated for light chopped at frequencies between 1 Hz and 100 kHz in the temperature range between 300 and 1.6 K. The responses to different chopping frequencies exhibited different temperature dependences. A marked decrease in photocurrent was observed under an applied magnetic field below 10 K.

We investigated the ground state of a highly one-dimensional conductor, TPP[Co(Pc)(CN)₂]₂ (TPP = tetraphenylphosphonium and Pc = phthalocyanine), by the measurement of the X-ray diffraction, electron spin resonance, nuclear quadrupole resonance, and magnetoresistance. An increase of the magnetic fluctuations was observed below 20 K, where no structural deformation was detected. In the ⁵⁹Co nuclear quadrupole resonance, we found an asymmetric broadening of the spectra owing to the intrinsic inhomogeneity of the molecular charge. We propose that the ground state is characterized by a weak charge disproportionation with antiferromagnetic fluctuations due to the high one dimensionality. A large magnetoresistance was observed under a high magnetic field. Spin effects are dominant at low fields. The anisotropic magnetoresistance suggests a change in the ground-state nature above 10 T.

The diffusion reaction of TBA(2)Cu(II)Cl(4) (TBA = tetrabutylammonium) and a N-containing organic donor, BP-TTF [=bis(pyrazino)-tetrathiafulvalene], yielded a 3-D supramolecular Cu complex, [CuCl2(BP-TTF)] (1). The magnetic measurement of 1 exhibits an antiferromagnetic interaction by fitting a Bonner-Fisher model from 2 to 300 K with S = (1)/(2) and J = -3.5 K between Cu-II mediated by self-assembling donor columns.

We fabricated ITO/biomolecule/Al junctions using chrolophyll a, cytochrome c, myoglobin, hemin, Vitamin B-12. All the junctions worked as organic light-emitting diode (OLED). The quantum efficiencies of the fabricated OLED were of the order of 1 x 10(-7) around V = 10 V, and did not seriously depend on whether or not a compound exhibits photoluminescence. Based on the energy diagram of the ITO/cytochrome c/Al junction, we discuss the difference of the EL spectrum from the photoluminescence or absorption spectrum. (c) 2005 Elsevier B.V. All rights reserved.

We have measured the thermal conductivity of organic molecular crystals (DMe-DCNQI)(2)Li1-xCux (x = 1 and 0.75) over a wide temperature range between 4 and 250 K. The electronic contribution can be analyzed particularly below similar to 80 K. A thermal hysteresis depending on the Cu concentration x has been observed between the heating and cooling processes. The system stays in a metallic state when the sample is cooled from room temperature, while a small fraction of insulating islands is created in the metallic state when heated up to room temperature. The insulating islands survive even at high temperatures. This mechanism gives rise to the hysteretic behavior. Heat conduction is sensitive to the difference in the two phases, in contrast with electrical resistivity.

Materials containing Fe(Pc)(CN)₂ dicyano(phthalocyaninato)iron molecules show a giant negative magnetoresistance from the interaction between the conduction and the local moment. Under a magnetic field, the resistance becomes two orders of magnitude smaller than the zero-field resistance. The magnetic-field-angle dependence of the magnetoresistance reflects the symmetry of the Fe(Pc)(CN)₂ molecule. We discuss, according to the scaling relation, the correlation between the magnetoresistance and the molecular spin fluctuation.

The electronic phase separation on macroscopic scale is studied in the organic Mott system κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br by means of scanning microregion infrared spectroscopy using the synchrotron radiation. The phase separation appears in the vicinity of the Mott boundary in the single crystals of which the band width is controlled by partly substituting the BEDT-TTF molecule with the deuterated one. The transport properties under the phase separation are considered to be influenced by the percolation process of the domains. © Springer Science+Business Media, LLC 2006.

The quarter-filled pi band systems, (DMc-DCNQI)(2)M(M = Li1-xCux(x <= 0.14), Ag) were systematically studied with electron paramagnetic resonance (EPR). The intercolumn spin hopping rate D-perpendicular to in Li1-xCux-salt was obtained from the EPR linewidth. The temperature dependence of D, can be understood with the hole soliton model which also explains the DC conductivity. The pi - d mixing of the Cu-salt enhances both D-perpendicular to and sigma(perpendicular to) by 10(3) times more than the Li-salt, which is consistent with the fact that the only Cu-salt has three-dimensional Fermi surface, but that Ag-salt is one-dimensional in spite of the mixing enhancement of D-perpendicular to by 10 times more than the Li-salt.

The quarter-filled pi band systems, (DMc-DCNQI)(2)M(M = Li1-xCux(x <= 0.14), Ag) were systematically studied with electron paramagnetic resonance (EPR). The intercolumn spin hopping rate D-perpendicular to in Li1-xCux-salt was obtained from the EPR linewidth. The temperature dependence of D, can be understood with the hole soliton model which also explains the DC conductivity. The pi - d mixing of the Cu-salt enhances both D-perpendicular to and sigma(perpendicular to) by 10(3) times more than the Li-salt, which is consistent with the fact that the only Cu-salt has three-dimensional Fermi surface, but that Ag-salt is one-dimensional in spite of the mixing enhancement of D-perpendicular to by 10 times more than the Li-salt.

Conductors obtained from axially substituted phthalocyanine units are presented. In contrast to face-to-face one-dimensional stacking in conductors with planar phthalocyanins, various types of pi-pi stacking structures can be obtained owing to the slipped stacking.

We have fabricated ITO-insulator-Al junctions using cytochrome c and myoglobin as insulating layers. The junctions act as light-emitting diodes. The electro-luminescence (EL) spectra of these diodes exhibit broad peaks around 530 and 700 nm, and a weak shoulder around 410 nm. These features are consistent with the absorption spectra. Although the reproducibility of the data is quite poor for the current and the EL intensity, the external quantum efficiency obtained from the two quantities are well expressed by a function of the applied voltage. The quantum efficiency almost linearly increases above the applied voltage of 7 V and reaches to similar to 1X10(-7) at V= 14 V for both cytochrome c and myoglobin diodes.

We have measured the thermal conductivity for organic molecular crystals (DMe-DCNQI)(2)Li1-xCux (x = 0, 0.08, and 0.14) over a wide range of temperatures (4 similar to 250 K). A peak can be seen near similar to 20 K. The peak height decreases with decreasing x, and it completely vanishes for x = 0 specimen. This peak is created by a crossover between the phonon mean free path that diverges as T-2 and the phonon specific heat that decreases as T-3. In addition, we have also succeeded in observing the super-lattice patterns of 4k(F) and 2k(F) of (DMe-DCNQI)(2)Li1-xCux (x = 0 and 0.06) accompanied by the Peierls and the spin Peierls transitions by means of the synchrotron radiation X-ray in Tsukuba's Photon Factory. (c) 2005 Elsevier Ltd. All rights reserved.

We fabricated organic-light-emitting diode (OLED) from chlorophyll a, and measured electroluminescence (EL) and photoluminescence (PL) spectra. The EL spectrum exhibits a peak at 700 nm and a shoulder at 750 nm, while the PL spectrum exhibits a peak at 750 nm. The external quantum efficiency of the fabricated OLED linearly increases for the applied voltage above V = 4 V and reaches to 9 × 10^−8 at V = 8 V.

Nearly isotropic two-dimensional sheets of partially oxidized Co(Pc)(CN)₂ units were observed to form in a salt with PXX (PXX = peri-xanthenoxanthene), [PXX]₂[Co(Pc)(CN)₂]·CH₃CN. The crystal is semiconducting under ambient pressure but displays stable metallic behavior under high pressure.

The anisotropic transfer integrals characterizing the quasi-one-dimensional (Q1D) electronic structure are determined experimentally for the new organic superconductor (DMET)(2)CuCl2 by angle-dependent magnetoresistance and polarized reflectance measurements. Lebed resonances and third angle effect are observed in the angle-dependent magnetoresistance; the latter gives the ratio of the inter- and intra-stack transfer integrals as t(a')/t(b)=0.1. From the anisotropy of the plasma frequency found in the polarized reflectance spectra, the intra- and inter-stack transfer integrals are deduced as t(b)=0.28 eV and t(a')=0.028 eV, respectively, in good agreement with the results of the third angle effect. The observed anisotropy of the transfer integrals is the same as those for the Q1D TMTSF salts, which is consistent with the appearance of the field-induced spin-density-wave states at magnetic fields similar to those of the Q1D TMTSF salts.

We have measured the thermal conductivity of organic molecular crystals (DMe-DCNQI)(2)Li1-xCux (0 <= x <= 0.14) over a wide temperature range between 4 and 250 K. We observed the phonon contribution in the whole range measured. A phonon peak was observed near similar to 20 K. This peak denotes a crossover between the phonon mean free path that diverges as T-2 and the phonon specific heat that decreases as T-3. The peak height decreases with the reduction of Cu concentration x and vanishes in the x=0 sample. We discuss this behavior in terms of the spin-Peierls local lattice distortion.