Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/chem.202104316

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： doi.org/10.7566/JPSJ

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We report Se-77 NMR measurements of high-quality polycrystals on the intercalated iron selenide superconductor Li-x(NH3)(y)Fe2-delta Se2, which has a high superconducting transition temperature T-c of 44 K. In the superconducting state, the temperature (T) dependence of the nuclear spin relaxation rate 1/T-1 decreases sharply without a coherence peak below T-c; this behavior can be reproduced by unconventional superconducting states with sign-reversal gap function. In the normal state, the Knight shift (K) and 1/T1T decrease significantly upon cooling, which is characteristic of heavily electron-doped FeSe-based compounds. A comparison of the T dependences of K and 1/T1T reveals that moderate spin fluctuations appear at high temperatures and are gradually suppressed upon cooling below 200 K, suggesting a spin-gap feature in the spin fluctuation spectrum at low energies. We note that these features are widely observed in many heavily electron-doped high-T-c FeSe-based superconductors that possess the characteristic electronic configuration dominated by large electron Fermi surfaces and a sinking hole-like pocket (or incipient band) around the Fermi level. It is in contrast to the typical Fe-based compounds characterized by hole and electron FSs with similar sizes, such as bulk FeSe, where spin fluctuations are significantly enhanced at low energies toward low temperatures. We discuss the universality and diversity of the relationships between the characteristics of the spin fluctuations and superconductivity in Fe-based compounds.

DOI： 10.7566/JPSJ.90.124709

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We have investigated the low-temperature magnetism of sodium superoxide (NaO2), in which spin, orbital, and lattice degrees of freedom are closely entangled. The magnetic susceptibility shows anomalies at T-1 = 220 K and T-2 = 190 K, which correspond well to the structural phase transition temperatures, and a sudden decrease below T-3 = 34 K. At 4.2 K, the magnetization shows a clear stepwise anomaly around 30 T with a large hysteresis. In addition, the muon spin relaxation experiments indicate no magnetic phase transition down to T = 0.3 K. The inelastic neutron scattering spectrum exhibits magnetic excitation with a finite energy gap. These results confirm that the ground state of NaO2 is a spin-singlet state. To understand this ground state in NaO2, we performed Raman scattering experiments. All the Raman-active libration modes expected for the marcasite phase below T-2 are observed. Furthermore, we find that several new peaks appear below T-3. This directly evidences the low crystal symmetry, namely, the presence of the phase transition at T-3. We conclude that the singlet ground state of NaO2 is due to the spin-Peierls instability.

DOI： 10.1103/PhysRevB.104.L140402

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Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1088/1742-6596/1

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

We report NMR experiments on heavily electron-doped Fe-based superconductor in comparison with the results on the parent Fe-based compounds. The typical parent Fe-based compound LaFe(As_1-x′P_x′)O exhibits the re-emergent antiferromagnetic (AFM) order at x′ ~ 0.6 (AFM2) separated from the parent AFM order at x′ =0 (AFM1). Systematic ³¹P-NMR study on [Sr₄Sc₂O₆]Fe₂(As_1−xP_x)₂ (SrSc42622), which has local lattice parameters of iron-pnictogen (FePn) layer similar to the series of LaFe(As_1−x′/P_x′)O, also revealed that the presence of AFM1 order is universal for most of parent Fe-based compounds. In contrast, the static AFM2 order was absent in this series, however, the dynamical low-energy AFM spin fluctuations are enhanced at around x ~ 0.8, indicating that the onset of the static AFM2 is quite sensitive to the local lattice parameters of FePn layer. In order to elucidate the further universality and diversity, we have carried out ⁷⁷Se-NMR measurement on Li_x(NH₃)_yFe_2−δSe₂ (T_c = 44 K) in heavily electron-doped regime. Although the spin fluctuations at low energies does not significantly develops upon cooling, the moderate spin fluctuations were extracted at high temperatures from comparison of the temperature (T) dependences of Knight shift and nuclear relaxation rate (1/T₁T). We discuss the universality and diversity of the relationship between the T_c and the characteristics of the spin fluctuations in the Fe-based compounds from a microscopic point of the NMR measurements.

DOI： 10.1088/1742-6596/1975/1/012008

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Other Link： https://iopscience.iop.org/article/10.1088/1742-6596/1975/1/012008/pdf

Publishing type：Research paper (scientific journal)  

© 2020 IOP Publishing Ltd. We report here the superconducting properties of a Laves phase superconductor SrIr2, which has a cubic MgCu2 structure. SrIr2 is a type-II superconductor, with a T c of 5.9 K. The estimated superconducting parameters of lower critical field µ 0 H c1 and upper critical field µ 0 H c2, coherence length ξ(0), penetration depth λ(0) and Ginzburg-Landau (GL) parameter κ(0) are approximately µ 0 H c1 = 101 Oe, µ 0 H c2(0) = 5.9 T, ξ(0) = 7.47 nm, λ(0) = 237 nm, and κ(0) = 31.7, respectively. The specific-heat data indicate that SrIr2 is a strong-coupling superconductor because the value of ΔC/γT c is approximately 1.71, which is larger than the value of 1.43 that is expected from the BCS theory. The physical properties obtained in this study are explained well by theoretical calculations including spin-orbit coupling (SOC). This result indicates that the physical properties of SrIr2 are strongly affected by the presence of SOC.

DOI： 10.1088/1361-648X/ab6a2e

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Topological superconductors have attracted wide-spreading interests for the bright application perspectives to quantum computing. Cu_0.3Bi₂Se₃ is a rare bulk topological superconductor with an odd-parity wave function, but the details of the vector order parameter d and its pinning mechanism are still unclear. Here, we succeed in growing Cu_xBi₂Se₃ single crystals with unprecedented high doping levels. For samples with x  = 0.28, 0.36 and 0.37 with similar carrier density as evidenced by the Knight shift, the in-plane upper critical field H_c2 shows a two-fold symmetry. However, the angle at which the H_c2 becomes minimal is different by 90° among them, which indicates that the d-vector direction is different for each crystal likely due to a different local environment. The carrier density for x  = 0.46 and 0.54 increases substantially compared to x ≤ 0.37. Surprisingly, the in-plane H_c2 anisotropy disappears, indicating that the gap symmetry undergoes a transition from nematic to isotropic (possibly chiral) as carrier increases.

DOI： 10.1038/s41467-019-14126-w

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Other Link： https://www.nature.com/articles/s41467-019-14126-w

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>A superconducting KBi₂ sample was successfully prepared using a liquid ammonia (NH₃) technique.</p>

DOI： 10.1039/d0ra04541a

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7566/JPSJ.88.0437

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

X-ray powder diffraction (XRPD), magnetic susceptibility and muon-spin relaxation (mu SR) measurements were carried out to investigate lattice symmetries and magnetic properties of one of alkali-metal superoxides, RbO2. Two structural transitions were observed around 170 and 100K in conjunction with the appearance of anomalies in the magnetic susceptibility. A static antiferromagnetic long-range ordered state of unpaired spins on O-2(-) dumbbells with the full magnetic volume fraction was confirmed from mu SR below about 15 K. In comparison with CsO2, it is suggested that small changes in the lattice symmetry driven by changes in the O-2(-) dumbbell orientation causes different magnetic properties in alkali-metal superoxides.

DOI： 10.7566/JPSJ.88.043701

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics Inc.  

Metal intercalation using a solvent has produced significant advances in the development of Fe-chalcogenide superconducting materials. Recently, the superconducting transition temperature (TC) of metal-intercalated FeSe has been raised to 46 K using ammonia as the solvent for the alkali-metal atom. However, multiple superconducting phases have been found, which may arise from different concentrations of intercalants, further complicating the situation. Here, we report the synthesis of single-crystals of metal-intercalated FeSe superconductors using liquid ammonia, and their physical properties. Particularly, utilization of single-crystals allows us to investigate the resistivity in these ammoniated metal-intercalated FeSe superconductors, Ax(NH3)yFe2-δSe2, for the first time. Firstly, we compared with their TC s and the interlayer distance between the FeSe layers (dI) as a function of ionic radius (r) of the exchangeable intercalant. We found that both TC and dI show weak dependence on the r, if the r is smaller than the effective size of another intercalant, i.e., NH3 molecule. Besides the enhancement of the dI by the insertion of NH3 molecule, one expects that the charge-transfer due to the intercalation of cation would leads to the shift of the Fermi energy. The intercalants (Ba and K) have similar rs, but different valences (Ba2+ and K+), which may throw light on the significance of charge transfer. When the metal concentrations were investigated on the cleaved surfaces of these single crystals, clear differences were found between the two compounds, with the K-concentration about double the Ba-concentration, which may imply the identical charge-transfer. This was also supported for the investigation of the Li-concentration. These results suggest not only the local environment within the conductive FeSe layers but also the significance of the number of electronic charges supplied to the FeSe layers by the intercalated metal and/or ammonia molecules.

DOI： 10.1063/1.5022120

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

We performed X-ray diffraction (XRD) and DC magnetic susceptibility measurements to elucidate the crystal structure and superconducting properties of KSr2Nb3O10. From the diffraction pattern indexing, it was found that KSr2Nb3O10 crystallizes with monoclinic symmetry, space group P21/m(11). We succeeded in preparing high temperature (HT) and low temperature (LT) phases of KSr2Nb3O10 powder samples synthesized by a conventional solid state reaction and an ion-exchange reaction, respectively. Superconductivity was observed at 4 K by Li intercalation and it was found that the superconducting volume fraction of the LT phase (~ 1.4%) is clearly larger than that of the HT phase (0.07%).

DOI： 10.1016/j.physb.2017.09.060

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

Alkali superoxide CsO2 is one of the candidates for the spin-1 2 one-dimensional (1D) antiferromagnet, which may be sequentially formed by an ordering of the π-orbital of O2 molecule below TS ∼ 70 K. Here, we report the magnetism and the high-magnetic field magnetization in pulsed-magnetic fields up to 60 T in powder CsO2. We obtained the low temperature phase diagram around the antiferromagnetic ordering temperature TN = 9.6 K under the magnetic field. At T = 1.3 K, we observed a remarkable up-turn curvature in the magnetization around a saturation field of ∼60 T, which indicates the low-dimensional nature of the spin system. The saturated magnetization is also estimated to be ∼1μB, which corresponds to spin-1 2. In this study we compare it with the theoretical calculation.

DOI： 10.7566/JPSJ.87.063704

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We investigate magnetic properties of an S = 1/2, quasi-one dimensional organic antiferromagnet, D-F5PNN using magnetization measurements taken at temperatures as low as 0.5 K. Three distinct phases were observed consisting of uniform, dimerized (D), and incommensurate (I) spin structures in the magnetic field versus temperature plane, where a significant hysteresis appears between DI transitions in the field scan measurements. A combination of magnon (S = 1) and soliton (S = 1/2) excitations have successfully reproduced the observed magnetic susceptibility. In addition, such excitations provide a reasonable interpretation of the temperature dependent electron spin resonance (ESR) spectra. These results indicate that D-F5PNN is an ideal candidate for studying the spin-Peierls transition.

DOI： 10.7566/JPSJ.86.113706

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Potassium-doped picene (K(3.0)picene) with a superconducting transition temperature (TC) 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 TC 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.

DOI： 10.1088/0953-8984/28/44/444001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

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.

DOI： 10.1088/0953-8984/28/33/334001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

We report syntheses of new superconducting metal-doped MoSe2 materials (MxMoSe2). The superconducting MxMoSe2 samples were prepared using a liquid NH3 technique, and can be represented as '(NH3)(y)MxMoSe2'. The T(c)s of these materials were approximately 5.0 K, independent of x and the specific metal atom. X-ray diffraction patterns of (NH3)(y)NaxMoSe2 were recorded using polycrystalline powders. An increase in lattice constant c showed that the Na atom was intercalated between MoSe2 layers. The x-independence of c was observed in (NH3)(y)NaxMoSe2, indicating the formation of a stoichiometric compound in the entire x range, which is consistent with the x-independence of T-c. A metallic edge of the Fermi level was observed in the photoemission spectrum at 30 K, demonstrating its metallic character in the normal state. Doping of MoSe2 with Li and K also yielded superconductivity. Thus, MoSe2 is a promising material for designing new superconductors, as are other transition metal dichalcogenides.

DOI： 10.1038/srep29292

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Recently, ammonia-thermal reaction has been used for molecular intercalation in layered FeSe, resulting a new Li-x(NH3)(y)Fe2Se2 superconductor with T-c similar to 45 K. Here, we have used temperature dependent extended x-ray absorption fine structure (EXAFS) to investigate local atomic displacements in single crystals of this new superconductor. Using polarized EXAFS at Fe K-edge we have obtained direct information on the local Fe-Se and Fe-Fe bondlengths and corresponding mean square relative displacements (MSRD). We find that the Se-height in the intercalated system is lower than the one in the binary FeSe, suggesting compressed FeSe4 tetrahedron in the title system. Incidentally, there is hardly any effect of the intercalation on the bondlengths characteristics, revealed by the Einstein temperatures, that are similar to those found in the binary FeSe. Therefore, the molecular intercalation induces an effective compression and decouples the FeSe slabs. Furthermore, the results reveal an anomalous change in the atomic correlations across T-c, appearing as a clear decrease in the MSRD, indicating hardening of the local lattice mode. Similar response of the local lattice has been found in other families of superconductors, e.g., A15-type and cuprates superconductors. This observation suggests that local atomic correlations should have some direct correlation with the superconductivity.

DOI： 10.1038/srep27646

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Language：English   Publishing type：Part of collection (book)   Publisher：Pan Stanford Publishing Pte. Ltd.  

DOI： 10.1201/b19365

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

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 C-60 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 (C-60 and FeSe). The metal atoms are effectively intercalated into the spaces in C-60 and FeSe solids by supplying an electric current between electrodes in a solvent that includes electrolytes. The recorded superconducting transition temperatures, T-c's, were the same as those of metal-intercalated C-60 and FeSe prepared using solid-reaction or liquid solvent techniques. This technique may open a new avenue in the search for organic / inorganic superconductors.

DOI： 10.1038/srep18931

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The temperature dependence of the Hall coefficient of CeIn3 under high pressure has been investigated. The absolute value of the Hall coefficient shows an anomalous increase below T* similar to 80K at ambient pressure. The increase in T* with increasing pressure is similar to the pressure dependence of the characteristic temperature where the resistivity reaches its maximum. The temperature variations below T* at various pressures are well scaled on a single curve that is the formula based on the two-fluid model. No effect of the antiferromagnetic fluctuations observed in CeTIn5 (T = Co, Rh, and Ir) is observed above 2K even near the critical pressure where antiferromagnetic ordering disappears.

DOI： 10.7566/JPSJ.84.123702

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The mineral tetrahedrite Cu12Sb4S13 exhibits a first-order metal-insulator transition (MIT) at T-MI = 85K and ambient pressure. We measured the 63Cu-NMR at ambient pressure and the resistivity and magnetic susceptibility at high pressures. Cu-63-NMR results indicate a nonmagnetic insulating ground state in this compound. The MIT is monotonically suppressed by pressure and disappears at similar to 1.0 GPa. Two other anomalies are observed in the resistivity measurements, and the pressure-temperature phase diagram of Cu12Sb4S13 is constructed.

DOI： 10.7566/JPSJ.84.093701

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

'Aromatic hydrocarbon' implies an organic molecule that satisfies the (4n + 2) pi-electron rule and consists of benzene rings. Doping solid aromatic hydrocarbons with metals provides the superconductivity. The first discovery of such superconductivity was made for K-doped picene (K(x)picene, five benzene rings). Its superconducting transition temperatures (T-c's) were 7 and 18 K. Recently, we found a new superconducting K(x)picene phase with a T-c as high as 14 K, so we now know that K(x)picene possesses multiple superconducting phases. Besides K(x)picene, we discovered new superconductors such as Rb(x)picene and Caxpicene. A most serious problem is that the shielding fraction is &lt;= 615% for K(x)picene and Rb(x)picene, and it is often similar to 1% for other superconductors. Such low shielding fractions have made it difficult to determine the crystal structures of superconducting phases. Nevertheless, many research groups have expended a great deal of effort to make high quality hydrocarbon superconductors in the five years since the discovery of hydrocarbon superconductivity. At the present stage, superconductivity is observed in certain metaldoped aromatic hydrocarbons (picene, phenanthrene and dibenzopentacene), but the shielding fraction remains stubbornly low. The highest priority research area is to prepare aromatic superconductors with a high superconducting volume-fraction. Despite these difficulties, aromatic superconductivity is still a core research target and presents interesting and potentially breakthrough challenges, such as the positive pressure dependence of T-c that is clearly observed in some phases of aromatic hydrocarbon superconductors, suggesting behavior not explained by the standard BCS picture of superconductivity. In this article, we describe the present status of this research field, and discuss its future prospects. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2015.02.015

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The pressure dependence of the superconducting transition temperature (T-c) and unit cell metrics of tetragonal (NH3)(y)Cs0.4FeSe were investigated in high pressures up to 41 GPa. The T-c decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The T-c vs. c plot is compared with those of various (NH3)(y)MxFeSe (M: metal atoms) materials exhibiting different T-c and c, showing that the T-c is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the T-c. No superconductivity was observed down to 4.3 K in (NH3)(y)Cs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the T-c 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, T-c 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.

DOI： 10.1038/srep09477

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Soft x-ray magnetic circular dichroism (XMCD) have been measured on the single crystal of the charge-ordered type multiferroelectric material LuFe2O4. By comparing the XMCD results with the bulk magnetizations, the valence-specific magnetizations (VSMs) of Fe2+ and Fe3+ ions are obtained. Both Fe2+ and Fe3+ ions show positive and negative remanent VSMs below the spin ordering temperature TSO∼250 K, showing the ferrimagnetic long-range ordering directly. Both of the remanent VSMs disappear above the TSO and the field dependencies of the VSMs behave in paramagnetic fashions with convex and concave curvatures. However, the signs of the VSMs of Fe2+ and Fe3+ remain opposite, nevertheless the system is in a paramagnetic phase. This is direct evidence of the robust antiferromagnetic interaction between Fe2+ and Fe3+ ions even above the TSO. As temperature increases, furthermore, the opposite VSM of Fe3+ is reversed around the three-dimensional charge ordering temperature TCO∼330 K showing that both net magnetic moments of Fe2+ and Fe3+ become parallel to the applied magnetic field. Possible correlation between these unusual magnetic behaviors and the ferroelectric properties of LuFe2O4 is discussed.

DOI： 10.1103/PhysRevB.91.014410

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Soft x-ray magnetic circular dichroism (XMCD) have been measured on the single crystal of the charge-ordered type multiferroelectric material LuFe2O4. By comparing the XMCD results with the bulk magnetizations, the valence-specific magnetizations (VSMs) of Fe2+ and Fe3+ ions are obtained. Both Fe2+ and Fe3+ ions show positive and negative remanent VSMs below the spin ordering temperature T-SO similar to 250 K, showing the ferrimagnetic long-range ordering directly. Both of the remanent VSMs disappear above the TSO and the field dependencies of the VSMs behave in paramagnetic fashions with convex and concave curvatures. However, the signs of the VSMs of Fe2+ and Fe3+ remain opposite, nevertheless the system is in a paramagnetic phase. This is direct evidence of the robust antiferromagnetic interaction between Fe2+ and Fe3+ ions even above the T-SO. As temperature increases, furthermore, the opposite VSM of Fe3+ is reversed around the three-dimensional charge ordering temperature T-CO similar to 330 K showing that both net magnetic moments of Fe2+ and Fe3+ become parallel to the applied magnetic field. Possible correlation between these unusual magnetic behaviors and the ferroelectric properties of LuFe2O4 is discussed.

DOI： 10.1103/PhysRevB.91.014410

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

Photoinduced growth of the antiferromagnetic state in the ferrimagnetic phase were demonstrated in double layered Fe oxide LuFe2O4 by 12 fs infrared pulse under inter-layer excitation. Inter-layer charge imbalance successively induces the changes of charge/magnetic structures interacting with local Fe-O stretching and inter-layer sliding phonons through the exchange interaction.

DOI： 10.1007/978-3-319-13242-6_61

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We fabricated picene thin-film field-effect transistors (FETs) with an ionic liquid gel and ionic liquid sheet as the gate electrolyte, and then used electron spin resonance (ESR) to investigate the carrier injection process in the organic electric double layer (EDL) FET. The ESR spectra strongly depended on the morphology of gate electrolytes. Three types of carrier injection processes in the EDL-FET were observed by examining the applied-bias time, organic-layer thickness, and gate-voltage dependencies of the electric-field-induced ESR spectrum: (1) interface injection due to electrostatic EDL formation, (2) bulk injection due to penetration of ions (electrochemical bulk doping), and (3) electrochemical reaction. These findings are significant for designing novel materials using the EDL-FET technique because three different carrier injection processes may lead to different physical properties, even in the same organic material. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2014.08.043

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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 a-phase and the antiferromagnetic alpha'-phase of tetra-kis-(dimethylamino)-ethylene-C-60 (TDAE-C-60)-as determined by dielectric measurements. We propose that the permanent electric dipole originates from the pairing of a TDAE molecule with surrounding C-60 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 a-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 C(60)s is also discussed.

DOI： 10.1038/srep06419

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Language：English   Publisher：WILEY-V C H VERLAG GMBH  

The characteristics of field-effect transistors (FETs) fabricated from thin films and single crystals of phenacene molecules are fully reported in this review together with the electronic and crystal structures of phenacenes. Phenacene molecules possess a low HOMO level and a wide band gap. The highest mobility observed in the phenacene thin-film FETs is 7.4 cm(2)V(-1)s(-1) for [6]phenacene, and in single-crystal FETs the highest value is 6.3 cm(2)V(-1)s(-1) for [7]phenacene. The phenacene thin-film FETs show O-2-sensing properties unlike their single-crystal FETs. The bias-stress effect is fully investigated for phenacene single-crystal FETs. Furthermore, the low-voltage operation of phenacene single-crystal FETs with electric-double-layer (EDL) capacitors is reported. The temperature dependence of phenacene single-crystal FETs is reported to clarify the transport mechanism, which is suggestive of band-like transport.

DOI： 10.1002/ejic.201402168

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We report the change in the magnetic properties of multiferroic YbFe2O4 caused by cooling in the presence of an electrical current. The magnetization measured after the cooling is similar to 10-20% smaller than that after cooling without a current. The current also affects the magnetic anisotropy below similar to 100 K; the magnetic coercivity is increased by similar to 10-20%. These phenomena may arise from the coexistence of ferromagnetic and antiferromagnetic domains or a disturbance in the formation of charge-ordered domains. From the viewpoint of application, the enhancement of anisotropy by an electrical current provides a method for stabilizing magnetization other than the well-known method of exchange bias.

DOI： 10.7566/JPSJ.83.063708

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Alkali-metal-intercalated FeSe materials, (NH3) yM0.4FeSe (M: K, Rb, and Cs), have been synthesized using the liquid NH3 technique. (NH3)yCs 0.4FeSe shows a superconducting transition temperature (T c) as high as 31.2 K, which is higher by 3.8 K than the Tc of nonammoniated Cs0.4FeSe. The Tcs of (NH 3)yK0.4FeSe and (NH3) yRb0.4FeSe are almost the same as those of nonammoniated K0.4FeSe and Rb0.4FeSe. The Tc of (NH 3)yCs0.4FeSe shows a negative pressure dependence. A clear correlation between Tc and lattice constant c is found for ammoniated metal-intercalated FeSe materials, suggesting a correlation between Fermi-surface nesting and superconductivity. © 2013 American Physical Society.

DOI： 10.1103/PhysRevB.88.094521

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The magnetic ground state of the fcc phase of the Mott insulator Cs 3C60 was studied using a low-temperature electron spin resonance technique, and antiferromagnetic resonance (AFMR) below 1.57 K was directly observed at ambient pressure. The AFMR modes for the fcc phase of Cs3C60 were investigated using a conventional two-sublattice model with uniaxial anisotropy, and the spin-flop field was determined to be 4.7 kOe at 1.57 K. The static magnetic exchange interactions and anisotropy field for fcc-Cs3C60 were also estimated. © 2013 IOP Publishing Ltd.

DOI： 10.1088/0953-8984/25/36/366001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The magnetocapacitance effect was investigated using impedance spectroscopy on single crystals of LuFe2O4. The intrinsic impedance response could be separated from the interfacial response and showed a clear hysteresis loop below T-Ferri similar to 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 LuFe2O4. DOI: 10.1103/PhysRevLett.110.117602

DOI： 10.1103/PhysRevLett.110.117602

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Field-effect transistor (FET) devices using thin crystals of FeSe1-xTex (x = 0.9 and 1.0) have been fabricated with an electric-double-layer (EDL) capacitor. Despite the presence of substantial quantities of electron and hole carriers in the bulk due to the semimetallic electronic structure of FeSe1-xTex, we have observed p-channel depletion-type FET characteristics, in contrast to the n-channel normally on FET characteristics of a Bi2Se3 EDL FET. In FeSe1-xTex, the mobile carriers, holes, are depleted in the channel region by accumulating electrons, resulting in a decrease in conductivity. This result is consistent with the experimentally observed positive Hall coefficient at room temperature. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795626]

DOI： 10.1063/1.4795626

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report the observation of zero resistivity (rho) in a hydrocarbon superconductor, and describe the temperature dependence of 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 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-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-c's of both the 7 and 18 K phases of K(3)picene reported previously. The temperature dependence of rho for both samples exhibits granular-metal-like behavior in the normal state. DOI: 10.1103/PhysRevB.87.060505

DOI： 10.1103/PhysRevB.87.060505

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DOI： 10.1103/PHYSREVB.87.060505

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

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. (c) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jlumin.2011.12.051

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We have investigated the magnetic properties of a single crystal of multiferroic YbFe2O4. Ferrimagnetic ordering of Fe spins is observed at similar to 250 K. The magnetization measured during field cooling becomes negative below similar to 10 K owing to the antiparallel coupling between the Fe and Yb sublattices. The magnetization below similar to 10 K is flipped by changing the applied magnetic field in a positive direction, a property which may be used to the development of magnetic devices. Magnetocaloric measurements show a broad peak of the entropy change, likely owing to a multiple magnetic transition.

DOI： 10.1088/1742-6596/428/1/012032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

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.

DOI： 10.1080/00150193.2013.773874

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We have investigated the magnetic properties of R2Fe 3O7 (R=Yb and Lu), which belongs to the homologous family of electronic ferroelectric RFe2O4. Magnetization measurements show ferrimagnetic ordering at the Néel temperature (T N) of ∼270 K, which is slightly higher than that of RFe 2O4 (TN∼230-250 K). Observation of spin glass and exchange bias shows a coexistence of ferromagnetic and antiferromagnetic interactions, similarly to RFe2O4. This situation gives rise to a complex magnetic change and a broad peak of magnetic entropy change. Some characteristics, such as refrigeration temperatures higher than in RFe2O4, seem to offer a possibility of this system to applications. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2013.08.030

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report electronic-structure and physical properties of metal-doped picene as well as selective synthesis of the phase that exhibits 18-K superconducting transition. First, Raman scattering is used to characterize the number of electrons transferred from the dopants to picene molecules, where a softening of Raman scattering peaks 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 pressure dependence of T-c in 7- and 18-K phases of K(3)picene. The 7-K phase shows a negative pressure dependence, while the 18-K phase exhibits a positive pressure dependence which can not be understood with a simple phonon mechanism of BCS superconductivity. Third, we report a synthesis method for superconducting K(3)picene by a solution process with monomethylamine CH3NH2. This method enables us to prepare selectively the K(3)picene sample exhibiting 18-K superconducting transition. The method for preparing K(3)picene with T-c = 18 K found here may facilitate clarification of the mechanism of superconductivity.

DOI： 10.1103/PhysRevB.86.214507

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

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 cm(2) 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 X 10(-1) cm(2) V-1 s(-1) and low absolute value, 1.9 V, of threshold voltage.

DOI： 10.1021/jp300052p

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

An exchange bias (EB) behavior has been observed for multiferroic RFe2O4 (R Y, Er, Tm, Yb, Lu, and In). The materials with small R3+ ions (R = Tm, Yb, Lu, and In) exhibit large EB fields (greater than or similar to 1 kOe) below similar to 100-150 K. This property is rooted in a magnetically glassy state, arising from the competition between ferromagnetic and antiferromagnetic domain interactions. In addition, the EB field tends to be more enhanced for smaller R3+ ions. Hence, the EB is controlled by the substitution at the R-site in this series.

DOI： 10.1143/JPSJ.81.033704

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

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[PF6]), 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 mu for [7]phenacene TFT with bmim[PF6] was recorded to be 0.28 cm(2) V-1 s(-1). The value of absolute threshold voltage, vertical bar V-TH vertical bar, 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. (C) 2011 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.orgel.2011.08.016

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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 similar to 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. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2011.05.049

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Soft x-ray photoelectron spectroscopy was performed for alpha-TDAE-C-60 single crystal. A C 1s spectrum with a shakeup satellite of TDAE-C-60 is very similar to that of C-60 when we shift the energy, indicating a charge transfer to the C-60 site. A comparison of a N 1s spectrum with theoretical calculations indicates that TDAE mainly consists of the TDAE(+) state. The valence-band spectrum near the Fermi edge also suggests a charge transfer from the TDAE to the C-60 cage. Based on these results we propose a modified model for the charge transfer: the charge states of C-60(-) and TDAE(+), and the dimer formation along the c axis between the TDAE(+) states.

DOI： 10.1103/PhysRevB.84.161404

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Superconductivity was recently discovered in solid potassium-intercalated picene (K(3)22ph), in which the picene molecule becomes trianionic (22ph(3-)). In this Letter, we conduct a theory-based study of the superconductivity of 22ph(3-) within the framework of BCS theory. We estimate the density of states N(epsilon(F)) on the Fermi level to be 2.2 states per (eV molecule spin) by using the theoretical intramolecular electron-phonon coupling l(x) and the experimental superconducting transition temperature T-c of 18 K. The theoretical value is consistent with the 1.2 states per (eV molecule spin) determined experimentally for K(3)22ph with T-c = 18 K, indicating the validity of our theoretical treatment and the electron-phonon mechanism for superconductivity. The predicted l(x), 0.206 eV, for 22ph(3-) is larger than any value reported for organic superconductors, so picene may have the largest l(x) among the superconductors reported so far.

DOI： 10.1103/PhysRevLett.107.077001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The electronic properties of Eu2.75C60 are studied using magnetic susceptibility and electron spin resonance (ESR) from 2 to 300 K. Both the magnetic susceptibility and the ESR parameters clearly show an anomaly around the valence transition temperature, T-V = 70 K. The magnetic susceptibility shows weak temperature dependence above T-V, while it changes drastically to Curie-Weiss behavior below T-V. The low-temperature susceptibility can be reproduced by assuming the moment of free Eu2+ ions. This result reveals that Eu2.75C60 changes from the intermediate valence state to the divalent state below T-V. Although ESR signals above T-V should be attributed to conduction electrons, the ESR intensity below T-V follows the Curie-Weiss law with a distinct increase in the g-factor. This should be associated with a strong localization of pi electrons. We also found that, below similar to 17 K, the isothermal magnetization exhibits a weak hysteresis and thermoremanent magnetization appears. These results suggest that valence-ordered Eu2.75C60 undergoes antiferromagnetic ordering with a weak ferromagnetic component at the Neel temperature, T-N = 17 K.

DOI： 10.1103/PhysRevB.83.245103

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The frequency dependence of the complex dielectric constant of LuFe2O4 single crystal is measured by terahertz time-domain spectroscopy. We observed a broad infrared active mode in the real and imaginary parts of the complex dielectric constants at around 25 cm(-1).

DOI： 10.1109/irmmw-THz.2011.6104854

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

Changes of charge ordered (CO) structure by partial substitution of Mn for Fe in YbFe2O4 were investigated by a transmission electron microscope (TEM), in combination with conventional dielectric measurement. It is revealed that partial substitution of Mn2+ for Fe2+ in YbFe2O4 destroyed drastically the CO structure with the wave vector of q=&lt;1/3 1/3 1/2&gt;. Consequently polar clustering structure giving rise to honeycomb-shaped diffuse streaks was found in YbFeMnO4. The random distribution of polar clustering structure gives rise to characteristic broad dielectric dispersion.

DOI： 10.1088/1757-899X/18/9/092047

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

New carbon-based superconductors are synthesized by intercalating metal atoms into the solid-phase hydrocarbons picene and coronene. The highest reported superconducting transition temperature, T-c, of a hydrocarbon superconductor is 18 K for K(3)picene. The physics and chemistry of the hydrocarbon superconductors are extensively described for Axpicene (A: alkali and alkali earth-metal atoms) for x = 0-5. The theoretical picture of their electronic structure is also reviewed. Future prospects for hydrocarbon superconductors are discussed from the viewpoint of combining electronics with condensed-matter physics: modification of the physical properties of hydrocarbon solids is explored by building them into a field-effect transistor. The features of other carbon-based superconductors are compared to clarify the nature of hydrocarbon superconductors.

DOI： 10.1039/c1cp20961b

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

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.

DOI： 10.1080/00150193.2011.577294

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The variation of AC dielectric constant in the function of the DC magnetic fields was found in low oxygen vacant LuFe2O4 single crystal in which the electric polarization arise from the polar charge ordering. These magneto-electric coupling should be explained by a novel mechanism where the boundary motion of the polar charge ordered domain is affected by the magnetic (spin) domain boundary motion.

DOI： 10.1080/00150193.2011.577371

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We use photoemission spectroscopy to study electronic structures of pristine and K-doped solid picene. The valence band spectrum of pristine picene consists of three main features with no state at the Fermi level (E(F)) while that of K-doped picene has three structures similar to those of pristine picene with new states near E(F), consistent with the semiconductor-metal transition. The K-induced change cannot be explained with a simple rigid-band model of pristine picene but can be interpreted by molecular-orbital calculations considering electron-intramolecular-vibration interaction. Excellent agreement of the K-doped spectrum with the calculations points to importance of electron-intramolecular-vibration interaction in K-doped picene.

DOI： 10.1103/PhysRevB.82.195114

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

O-2 gas sensing behaviors are studied in picene thin film field-effect transistors (FETs) with hydrophobic polymer (Cytop(TM) 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 O-2 gas sensing effects down to similar to 10 ppm. A quantitative analysis is presented of the gate voltage (V-G) dependent mobility induced by O-2 exposure, i.e., the suppression of drain current at high V-G. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2010.06.003

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The kinetic energy of alpha&apos;-(BEDT-TTF)(2)IBr2 alpha-(BEDT-TTF)(2)I-3 and alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4) was estimated from the room-temperature optical conductivity measured from 50 to 30 000 cm(-1) The kinetic energy of alpha-(BEDT-TTF)(2)IBr2 was significantly smaller than that of alpha-(BEDT-TTF)(2)I-3 that shows metal-insulator phase transition A clear hysteresis was found in the magnetic susceptibility near the phase transition at around 30 K (C) 2010 Elsevier B V All rights reserved

DOI： 10.1016/j.physb.2010.01.082

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We present the field and temperature behavior of the narrow electron spin resonance (ESR) response in YbRh2Si2 well below the single ion Kondo temperature. The ESR g-factor reflects a Kondo-like field and temperature evolution of the Yb3+ magnetism. Measurements toward low temperatures (&gt;0.5 K) have shown distinct crossover anomalies of the ESR parameters upon approaching the regime of a well-defined heavy Fermi liquid. Comparison with the field dependence of specific heat and electrical resistivity reveal that the ESR parameters can be related to quasiparticle mass and cross section and, hence, contain inherent heavy electron properties. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.200983058

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

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 compounds(1), boron-doped diamond(2) and-most prominently-iron arsenides such as LaO(1-x)F(x)FeAs (ref. 3). In the case of organic superconductors, however, no new material system with a high superconducting transition temperature (T(c)) 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 T(c) values of 7K and 18 K, depending on the metal content. The drop of magnetization in Kxpicene solids at the transition temperature is sharp (&lt;2 K), similar to the behaviour of Ca-intercalated graphite(1). The Tc of 18K is comparable to that of K-intercalated C(60) (ref. 4). This discovery of superconductivity in K(x)picene shows that organic hydrocarbons are promising candidates for improved T(c) values.

DOI： 10.1038/nature08859

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

A magneto-electric (ME) effect was observed in a charge-ordered ferroelectric LuFe2O4. The dielectric response in a three-dimensional charge-ordered phase is strongly influenced by magnetic field, especially around the fern-magnetic ordering temperature. We also show the relation between the oxygen stoichiometry and the ME signal character above the magnetic transition temperature.

DOI： 10.1088/1742-6596/200/1/012077

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We investigated the average crystal structure and microstructures of LuFe0.56Ti0.44O3 by transmission electron microscopy (TEM) in combination with dielectric measurements. In this work, high-quality polycrystalline samples of LuFe0.56Ti0.44O3 were successfully synthesized in air by the conventional solid-state reaction. The average crystal structure at room temperature is characterized by a hexagonal structure (space group: P6(3)cm). Dielectric measurements revealed that LuFe0.56Ti0.44O3 shows broad dielectric peaks at approximately 450 and 580 K, one of which is considered to originate from the formation of polar domains at the nanometer scale. (C) 2009 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.48.09KB04

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

C-60 and picene thin film field-effect transistors (FETs) in bottom contact structure have been fabricated with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PED-OT:PSS) electrodes for a realization of mechanical flexible organic FETs. The C-60 thin film FETs showed n-channel enhancement-type characteristics with the field-effect mobility mu value of 0.41 cm(2\) V-1 s(-1), while the picene thin film FET showed p-channel enhancement-type characteristics with the p of 0.61 cm(2) V-1 s(-1). The p values recorded for C-60 and picene thin film FETs are comparable to those for C-60 and picene thin film FETs with Au electrodes. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2009.01.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

We report dielectric and magnetic properties of a single crystal of LuFe2O4 with different degrees of oxygen deficiency. The oxygen stoichiometry was monitored with the gas mixture ratio of CO2 and CO during the crystal growing process. A sample having high resistivity of about 10 k 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.

DOI： 10.1080/00150190902859187

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

Raman spectrum and second-harmonic generation measurements have been performed for an organic conductor α-(ET)2I2Br [ET: bis(ethylenedithio)tetrathiafulvalene]. The Raman spectrum showed splitting of a charge sensitive mode at low temperatures, illustrating that the metal-to-insulator transition of the compound is ascribed to charge ordering. Critical appearance of the second-order nonlinear optical signal below the transition temperature manifests that the inversion symmetry of the crystal is annihilated by the charge ordering to generate permanent electric polarization. This is the second example of the verification of ferroelectric transition in an organic conductor. © 2008 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/132/1/012006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We have studied the ground state of a fullerene-based magnet, the alpha'-phase tetra-kis-(dimethylamino)ethylene-C-60 (alpha'-TDAE-C-60), by electron spin resonance and magnetic torque measurements. Below T-N = 7 K, nonparamagnetic field dependent resonances with a finite excitation gap ( 1.7 GHz) are observed along the a axis. Strong enhancement in their intensity as temperature is decreased is inconsistent with excitation from a singlet state, which had been proposed for the alpha'-phase ground state. Below T-N, nonquadratic field dependence of the magnetic torque signal is also observed in contrast to quadratic field dependence in the paramagnetic phase. The angle-dependent torque signals below T-N indicate the existence of an anisotropy of the bulk magnetization. From both experiments, we propose an antiferro-magnetic ground state driven by the cooperative orientational ordering of C-60 in the alpha'-TDAE-C-60.

DOI： 10.1103/PhysRevLett.99.177205

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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. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.313

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The magnetization measurements under pressure were performed on the fullerene-based ferromagnet, alpha-TDAE-C-60. We found that the saturation magnetization below the ferromagnetic ordering temperature T, is rapidly suppressed with increasing pressure and disappeared above P-c2 = 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, is almost pressure independent below P-e2, but, above P-e2 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,, as well as P,. We discuss these results compared with the high-pressure ESR. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.661

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We have studied the ground state of an organic quasi-one-dimensional (Q]D) ferromagnet, the gamma-phase para-nitrophenyl nitronyl nitroxide (gamma-p-NPNN), by low-frequency ESR and magnetic torque measurements, and have found that it is an anti ferro magnetically ordered state with an orthorhombic anisotropy. Antiferromagnetic resonance (AFMR) modes are observed below 0.6 K. From the angle dependence of AFMR, the spin easy axis is found to point the [011] direction. The spin-flop (SF) field is estimated to be 520 Oe. From the analysis of the AFMR modes in terms of a mean-field approximation, we have estimated the interchain interactions and the anisotropy field parameters in the ground state. The magnetic phase diagram along the spin easy axis has been determined using a high sensitive microcantilever technique. On the field dependence along the easy axis, the torque response shows anomalies at 520 Oe and around 2100 Oe, corresponding to the spin-flop and the full-polarization of spins, respectively. The easy axis and anisotropy in the antiferromagnetic state are found to be well explained by our calculations of the dipolar energy with respect to the spin structure obtained in this 41 work.

DOI： 10.1143/JPSJ.75.074702

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

We present the temperature-dependent infrared and Raman spectra of beta(')-(ET)(3)X-2 (X=HSO4 and ClO4; ET=bis-ethylenedithio-tetrathiafulvalene) compounds which undergo a metal-insulator transition. The infrared-active v(27) mode discontinuously split into two bands at the metal-insulator transition temperature of 127 K in the X=HSO4 salt, whereas, the corresponding mode continuously changed across the metal-insulator transition temperature of similar to 170 K in the X=ClO4 salt. In both compounds, the charge-sensitive v(27) mode split into two in the insulating phase. This drastic spectral change indicates that the metal-insulator transition originated in the charge ordering. Employing the frequencies of the split v(27) bands, the site charges are estimated to be +0.3(4) and +0.8(1) for X=HSO4 and +0.3(6) and +0.8(1) for X=ClO4. We also estimated the site charges using the Raman-active v(2) mode and obtained consistent results. Examining the selection rule of the v(3) mode, we reached the conclusion that the unit cell with space group P1 has a pseudoinversion center in the charge-ordered phase. Based on the symmetry, we propose a charge-ordering pattern for the X=HSO4 and X=ClO4 salts, which is quite different from that of the X=ReO4 salt reported previously. We qualitatively discuss the differences in the charge-ordering pattern considering the anisotropic intersite Coulomb interaction.

DOI： 10.1103/PhysRevB.73.125116

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The phase diagram of the mixed donor quasi one-dimensional (Q1D) metallic system (TMTSF1-xTMTTFx)(2)PF6 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.

DOI： 10.1007/s10909-006-9144-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP SCIENCES S A  

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.

DOI： 10.1051/jp4:2005131008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We performed the low-temperature and radio-frequency (rf) ESR of spherically molded single crystals of beta-p-NPNN in order to re-investigate the ferromagnetic resonance (FMR). The symmetric FM R 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 H-K = 61 G using the FMR relation with uniaxial anisotropy. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2005.03.051

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The low frequency (similar to 300 MHz) and low-temperature (0.4 K) ESR were performed in the gamma-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 x 0.10 x 0.10 mm(3). 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. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2005.03.052

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We found that the Field Induced Spin Density Wave (FISDW) phase in (DMET-TSeF)(2)I-3 has an apparent high threshold field of about 25 T in spite of the very similar room temperature crystal structure and the Fermi surface compared to the salts studied so far with anions AuCl2, AuBr2 and AuI2 which have threshold fields well below 10 T. The X-ray crystal structural studies down to 90 K do not show any special change in the structure. Possible reasons for the origin of the differences are discussed, and the sliding motion of the FISDW condensates at lower magnetic fields is proposed to be the most probable reason.

DOI： 10.1016/j.synthmet.2005.07.062

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We study the anisotropy of ESR parameters using single crystal TDA-E-C-60, which has two polymorphisms: the one is ferromagnetic alpha-phase and the other is non-ferromagnetic alpha'-phase. In both alpha'- and alpha- phase, the line-widths and g-factors show anisotropic angular dependences at room temperature, such as Delta H-pp(6) &gt; Delta H-pp(c) similar to Delta H-pp(a) and g(b) &gt; = 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 alpha'-phase the temperature dependence of g-factors has a clear anomaly around 160K. 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 alpha-phase, the g-factors continuously shift with decreasing temperature, become anisotropic below 230K, 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 a'- and a-phases. This difference separates the magnetic peculiarities of two polymorphisms in TDAE-C-60.

DOI： 10.1016/j.synthmet.2005.07.301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The low-temperature structure analysis and low-temperature ESR were performed in the gamma-phase of p-NPNN, which is considered to be as a quasi-one-dimensional ferromagnet above the antiferromagnetic ordering temperature (0.65K without a static magnetic field). No structural phase transition was observed below 30K, 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, contact gives rise to the strong ferromagnetic interaction. Below 0.6K, we succeeded in observing the anti ferro magnetic resonance (AFMR) using the low frequency (similar to 300 MHz) and low-temperature (0.5K) ESR. The frequency-field relation is well reproduced by the two-sublattice model with orthorhombic anisotropy.

DOI： 10.1016/j.synthmet.2005.07.077

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We present the optical conductivity and Raman spectra of theta-(BEDT-TTF)(2)CsZn(SCN)(4). The vibrational and vibronic bands in the 1200-1600cm(-1) region was assigned with the aid of the C-13- substituted compound. The nearly uniform charge distribution was found in a whole temperature range from 300 to 6 K. However, the space group symmetry I222 is locally broken already at room temperature. The broken symmetry suggests the resemblance to the high-temperature phase and frozen state of theta-(BEDT-TTF)(2)RbZn(SCN)(4), which consists of short-range ordered charge-ordering domains. The amplitude in the charge-ordering domain of theta-(BEDT-TTF)(2)CsZn(SCN)(4) is extremely small in a whole temperature range. At room temperature, hydrostatic pressure narrows the bandwidth of theta-(BEDT-TTF)(2)CsZn(SCN)(4) to enlarge the amplitude in short-ranged ordered domains. The long-range ordered charge ordering in theta-(BEDT-TTF)(2)CsZn(SCN)(4) Was found at 10 K under the hydrostatic pressure of 2.5 GPa.

DOI： 10.1143/JPSJ.74.2631

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

A new material of higher fullerene, RbxC84, was synthesized by intercalating Rb metal into C-84 crystals. The RbxC(84) crystals showed a simple cubic (sc) structure with lattice constant, a, of 16.82 (2) angstrom at 6.5 K, and 16.87 (2) angstrom at 295 K. The Rietveld refinements were achieved with the space group, Pa (3) over bar, based on a model that the C-2 axis of D2d-C84 aligned along [111]. The sample composition was determined to be Rb-8.8(7) C-84. The ESR spectrum at 303 K was composed of a broad peak with peak-to-peak linewidth Delta H-pp of 220 G, and a narrow peak with Delta H-pp of 24 G. Temperature dependence of the broad peak clearly showed a metallic behavior. The metallic behavior was discussed based on a theoretical calculation. This finding of new metallic phase in a higher fullerene is the first step for a development of new types of fullerene materials with novel physical properties such as superconductivity.

DOI： 10.1103/PhysRevB.71.224118

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A type of low-temperature structure for ferromagnetic alpha-tetra-kis (dimethylamino) -ethylene (TDAE)-C-60 is proposed on the basis of low-temperature x-ray analysis. We observed that intense superlattice reflections with odd indices successively appeared below T-s = 170 K. The space group symmetry of the low-temperature phase is determined to be P2(1)/n. Two inequivalent C-60 sites exist in the low-temperature phase, which are indispensable to the orbital ordering model Of C-60. The contact configuration for the neighboring C(60)s along the stacking c direction is uniquely determined. The double bond between the hexagons faces the neighboring pentagon. We found that the surrounding TDAE molecules shift along the c axis (similar to 0.07 angstrom) and that these shifts correlate perfectly to the alignment of C-60. This result indicates that the steric effect betwee n C-60 and TDAE molecules plays an important role in the orientational ordering Of C-60, On the other hand, in the alpha' phase, no structural phase transition was observed below 30 K. This indicates that all the C(60)s are crystallographically equivalent. Structural differences separate the magnetic peculiarities of the two polymorphs in TDAE-C-60.

DOI： 10.1103/PhysRevB.71.174424

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The polarized Raman and infrared spectra of theta-(ET)(2)CU2CN[N(CN)(2)](2) [ET = bis(ethylenedithio)tetrathiafulvalene] were measured at various temperatures below 300K. We investigated the three C=C stretching modes, V-2, V-3 and V-27. The spectral pattern is compatible with the horizontally charge-ordered state, where the site-charge distributions are +0.1(7) and +0.8(3). We have found that the vibronic V-3 bands correlate to the dihedral angles, psi, in the theta-ET salts. This relation is well reproduced by the numerical calculation based on the cluster model with C-2 symmetry. The spectral features suggest the dynamical fluctuation of nearly localized charges even above its phase transition temperature, similar to220 K.

DOI： 10.1143/JPSJ.73.2326

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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 T-s. The g-factor shows a clear shift around T-s 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 T-s and +3.42 K below T-s; respectively. These results suggest that the lattice distortion plays an important role on the low-temperature spin-gap state. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.480

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We found for the first time a structural phase transition in two-dimensional kagome antiferromagnet m-N-methylpyridinium alpha-nitronyl nitroxide (m-MPYNN)(.)BF(4)(.)1/3 (acetone). As, below T-s = 128.7 K, the intense satellite reflections are clearly observed at the modulation wave vector of q(s) = (1/3, 1/3, 0), the unit cell of the low-temperature phase is enlarged to root3a x root3a x c. In the low-temperature phase, the space group is determined to be P31c. 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 antiferromagnet.

DOI： 10.1143/JPSJ.73.796

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

High-pressure electron spin resonance (ESR) measurements were performed on tetrakis(dimethylamino) ethylene (TDAE)-C-60 single crystals and stability of the polymeric phase was established in the P-T parameter space. At 7 kbar the system undergoes a ferromagnetic to paramagnetic phase transition due to the pressure-induced polymerization. The polymeric phase remains stable after the pressure release. The depolymerization of the pressure-induced phase was observed at a temperature of 520 K, revealing an unexpectedly high thermal stability of the polymer. Below room temperature, the polymeric phase behaves as a simple Curie-type insulator with one unpaired electron spin per chemical formula. The TDAE(+) donor-related unpaired electron spins, formerly ESR silent, become active above a temperature of 320 K, which demonstrates that the magnetic properties are profoundly defined by miniscule reorientation of TDAE molecules.

DOI： 10.1103/PhysRevB.68.144430

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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.

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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.

DOI： 10.1143/JPSJS.72SB.151

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The eta-Mo4O11 system shows successive CDW transitions due to its two-dimensional Fermi surface instability. We find that the lower temperature CDW-II transition easily disappears by doping a small amount of W atoms (less than 0.2%/Mo), though the higher temperature CDW-I transition is weakly depressed. The W atoms possibly substitute both the intra- and the inter-layer Mo sites. The doping effectively reduce the carrier compensation, leading to the suppression of TCDW-I. Moreover, the interlayer coherence between the intralayer two-dimensional CDWs may be destroyed by the substitution between the layers since the modulation of CDW-II state has an interlayer component. The resistivity along the conducting plane follows "log T" dependence below 10 K, suggesting that the W atoms doped within the layer should induce the Anderson-type charge localization. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1386-9477(02)00963-3

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The high field Fermi surface in eta-Mo4O11 at low temperatures has been studied by the Angle-dependent Magnetoresistance Oscillation (AMMO) method (Organic Super Conductors, Springer, Berlin, 1998, p. 455). The Shubnikov-de Haas (SdH) oscillation so far obtained shows existence of the several closed surfaces, but the results only give the area of the pockets. The AMMO result at high fields in the plane perpendicular to the crystal b-axis shows the angle-dependent resistance oscillation together with the SdH oscillations. We see no clear AMMO for the fields in the plane perpendicular to the c-axis. The results indicate the existence of very anisotropic Fermi surfaces, which are expected from the Fermi surface model (Chem. Rev. 91 (1991) 965) taking into account the lower temperature CDW nesting vector q(2). (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1386-9477(02)00964-5

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The title quasi one-dimensional conductor with a half-filled energy band shows two kinds of modulated structures q(1) of (0 0 0.5) below 160 K and q(2) of (0.5 0 0.5) below 100 K. These wave vectors can nest Q1D Fermi surface. Two kinds of superlattice structures were solved using X-ray. In both cases, enhanced displacements of I-3 ions were observed. Their possible origins and their effects on the physical properties were discussed.

DOI： 10.1016/S0379-6779(02)00755-5

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The title compound is one of the DMET-TSeF salts which are quasi-one-dimensional organic metals at room temperatures. We show that the compound has a closed Fermi surface using the angle-dependent magnetoresistance oscillation (AMRO) method together with magnetoresistance and magnetization quantum oscillation measurements at low temperatures. By the X-ray measurement, we confirm that the structural phase transition observed around 180 K is related to the anomaly observed in the temperature dependence of the resistivity [1]. The nesting vector has the direction of 0.5a*+0.5c*. The obtained low temperature closed Fermi surface has about 4 % of the first Brillouin zone area. The AMRO data show the existence of a very anisotropic Fermi surface where the diameter perpendicular to the most conducting a direction is about 0.5 c*. The possible origin of the low temperature closed Fermi surface is discussed and the relation to the ordering of anion molecules is considered as the probable reason.

DOI： 10.1016/S0379-6779(02)00738-5

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The phase change due to the polymerization of the ferromagnetic tetrakis-dimethylamino-ethylene (TDAE)-C-60 has been reconfirmed by applying pressures in situ up to P-c = 7 kbar in an ESR cavity. This transition is irreversible and the phase above P-c is stable even after releasing pressure. The pressure-dependent g-factor indicates the revival of the TDAE(+) spins. Moreover, the ferromagnetism disappears simultaneously at P-c. The de-polymerization of the polymerized (pressure-released) crystal has been confirmed for the first time by the high-temperature ESR study. This transition is also irreversible and the polymer phase is stable up to 470 K. The de-polymerized phase is considered to be the original ferromagnetic one. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0379-6779(02)00432-0

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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. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0379-6779(02)00430-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OFICYNA WYDAWNICZA POLITECHNIKI WROCLAWSKIEJ  

The structure of [FeII(H3L)](ClO4)(2).3H(2)O, where H3L is a &lt;LF&gt;tripodal hexadentate ligand derived from the 1:3 condensation of tris(2-aminoethyl)amine and 4-formylimidazole, has been determined by X-ray crystallography at 113 and 293 K. A spin transition was inferred from the Fe-N bond distances. The temperature dependence of the magnetic susceptibility revealed that the complex undergoes a gradual spin transition in the temperature range of 150-270 K. A mixed-valence &lt;LF&gt;complex, [Fe-II(H3L)][Fe-III(L)]-(BF4)(2).1.5H(2)O, was &lt;LF&gt;prepared by the controlled deprotonation of the protonated species, [Fe-II(H3L)](BF4)(2).1.5H(2)O, under aerobic conditions, and the X-ray structure was determined at 293 K. Two species, [Fe-II(H3L)](2+) and [Fe-III(L)], are linked by imidazole-imidazolate (NH...H) hydrogen bonds to form a puckered sheet structure. Magnetic susceptibility measurements and Mossbauer spectra provided an evidence for spin-crossover at both the Fe-II and Fe-III sites. There are three accessible electronic states: (LS Fe-II-LS Fe-III), (HS Fe-II-LS Fe-III), and (HS Fe-II-HS Fe-III) that occur in passing from lower to higher temperatures.

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Raman spectra of (Me-2-DCNQI)(2)CuxLi1-x (0 less than or equal to x less than or equal to 1) have been measured at room temperature, 200 K, 100 K and 5 K. The observed Raman hands are assigned on the basis of the vibrational analysis done by Lunardi and Pecile. The Raman band assigned to the a(g)v(R8) fundamental mode (quinoid C=N stretching) shifts downward with an increase of x and exhibits a remarkable split for 0 less than or equal to x less than or equal to 0.29. This frequency shift is attributable to the change of a charge density on a Me-2-DCNQI molecule. From the split of the v(R8) Raman band, it is concluded that the charge densities on Me-2-DCNQI molecules are not equivalent even at room temperature for 0 less than or equal to x less than or equal to 0.29.

DOI： 10.1143/JPSJ.71.1956

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The intermediate phases Cs3+αC60 (α=0.0-1.0), have been prepared, and their structure and physical properties are studied by x-ray powder diffraction, Raman, ESR, electric conductivity, and ac susceptibility measurements under ambient and high pressures. The x-ray powder diffraction pattern of Cs3+αC60 (α =0.0-1.0) can be indexed as a mixture of the body-centered-orthorhombic (bco) and cubic (A15) phases. The A15 phase diminishes above 30 kbar. The broad ESR peak due to the conduction electron (c-ESR) is observed only for the phases around α=0.0 in Cs3+αC60. The resistivity of the Cs3+αC60 (α≠0) sample follows the granular metal theory and/or Sheng model even in the sample exhibiting a broad ESR peak. No superconducting transition is observed up to 10.6 kbar in (Cs3+αC60 (α≠0). These results present that bco phase of Cs3+αC60 (α=0) is a final candidate for a pressure-induced superconductor.

DOI： 10.1103/PhysRevB.65.235425

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The intermediate phases Cs3+alphaC60 (alpha=0.0-1.0), have been prepared, and their structure and physical properties are studied by x-ray powder diffraction, Raman, ESR, electric conductivity, and ac susceptibility measurements under ambient and high pressures. The x-ray powder diffraction pattern of Cs3+alphaC60 (alpha=0.0-1.0) can be indexed as a mixture of the body-centered-orthorhombic (bco) and cubic (A15) phases. The A15 phase diminishes above 30 kbar. The broad ESR peak due to the conduction electron (c-ESR) is observed only for the phases around alpha=0.0 in Cs3+alphaC60. The resistivity of the Cs3+alphaC60 (alphanot equal0) sample follows the granular metal theory and/or Sheng model even in the sample exhibiting a broad ESR peak. No superconducting transition is observed up to 10.6 kbar in Cs3+alphaC60 (alphanot equal0). These results present that bco phase of Cs3+alphaC60 (alpha=0) is a final candidate for a pressure-induced superconductor.

DOI： 10.1103/PhysRevB.65.235425

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The reaction of a tripodal ligand (H2L = N, N-bis(2-hydroxybenzyl)-N', N'-dimethylethylenediamine) with Cu(NO3)(2).3H(2)O and Cu(ClO4)(2).6H(2)O in methanol yielded [Cu-2 (HL)(2)](NO3)(2).H2O (1) and [Cu-2 (HL)(2)](ClO4)(2) (1'), respectively. When H2L was allowed to react with CuSO4.5H(2)O in the presence of triethylamine (1 : 1 : 2) in methanol, the neutral dicopper(II,II) complex [Cu-2 (L)(2)] (2) was obtained. The monopositive species [Cu-2 (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(mu-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.

DOI： 10.1039/b201741e

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The intermediate phases (formula presented) (formula presented) have been prepared, and their structure and physical properties are studied by x-ray powder diffraction, Raman, ESR, electric conductivity, and ac susceptibility measurements under ambient and high pressures. The x-ray powder diffraction pattern of (formula presented) (formula presented) can be indexed as a mixture of the body-centered-orthorhombic (bco) and cubic (formula presented) phases. The (formula presented) phase diminishes above 30 kbar. The broad ESR peak due to the conduction electron (formula presented) is observed only for the phases around (formula presented) in (formula presented) The resistivity of the (formula presented) (formula presented) sample follows the granular metal theory and/or Sheng model even in the sample exhibiting a broad ESR peak. No superconducting transition is observed up to 10.6 kbar in (formula presented) (formula presented) These results present that bco phase of (formula presented) (formula presented) is a final candidate for a pressure-induced superconductor. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.65.235425

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Using X-ray camera and diffractometer, structural evidence of the second CDW transition for the quasi two-dimensional conductor eta -Mo4O11 was presented. CDW critical wave vectors have been determined with high precision. Extremely weak satellite reflections at the reduced wave vector q(2)=(0.552 0.47 0.30) emerge below 25 K. Satellite reflections at the reduced wave vector q(1) = (0 0.232 0) was observed below 105 K.

DOI： 10.1016/S0379-6779(00)01192-9

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DMTCA-BF4 (C = S, Se) have been considered as a quasi-one-dimensional half-filled system. For both salts, the structural two-fold modulation along the stacking direction was observed from room temperature. We also found a rapid decrease in spin susceptibility of DMTSA-BF4 below 100 K, but no anomaly at the metal-insulator transition temperature (150 K).

DOI： 10.1016/S0379-6779(00)01126-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Cs K-edge XAFS of Cs(3)C(60) which is a pressure-induced superconductor were measured at 21 and 34 kbar by using a diamond anvil cell (DAC) in order to obtain the structural information under high pressure, and to clarify the origin of the pressure-induced superconductivity. The distances and the mean square displacements between the Cs and C atoms are consistent with those determined by X-ray powder diffraction. Consequently, the high-pressure XAFS can give the reliable structural-information on a fullerene superconductor under high pressure. We also show the procedure of the analysis of high-pressure XAFS with DAC in detail.

DOI： 10.1107/S0909049501000218

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The structure and physical properties of two-dimensional polymeric Na4C60 (body-centered monoclinic, space group I2/m) are studied in a wide temperature region from 12 to 300 K at 1 bar, and in a pressure region up to 53 kbar at 300 K. The temperature dependence of lattice constants suggests a structural anomaly below 100 K where the variation of spin susceptibility is observed from electron spin resonance. The thermal expansion of the unit-cell volume V is smaller than that of monomeric Rb3C60 and K3C60. The compressibility of c is larger than that of a and b, which can be well explained by the repulsion between Na ions. The compressibility of the center-to-center distance in the (10(1) over bar) plane is similar to1/3 times smaller that that in the (101) plane, which can be well explained by the formation of the polymer chains. Further, a possibility of a three-dimensional polymerization is discussed on the basis of the pressure dependence of C-60. . .C-60 distances.

DOI： 10.1103/PhysRevB.63.045418

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

The structural and magnetic properties are discussed on the TDAE-fullerene system for C-60 and C-70. The single crystal structural analysis reveals that the TDAE-C-70 system contains solvent molecules (toluene), and the C-70 molecules in the unit cell axe dimerized. The room temperature structure is monoclinic P2(1)/n, and crystal parameters are a=18.82(3)Angstrom, b=16.38(2)Angstrom, c=18.73(3)Angstrom and beta = 117.58(5)degrees. The same annealing procedure used in TDAE-C-60 does not alter the magnetic behavior in TDAE-C-70. A preliminary report is given for the TDAE-C-60 structural study in magnetic fields up to 7 T. The possible method that directly reveals the relation between magnetism and the molecular arrangement is proposed.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

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.

DOI： 10.1103/PhysRevB.61.R862

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Electron Spin-Echo (ESE) measurements on mixed-stack charge transfer compound tetrathiafulvalene (TTP)-chloranil (CA) are reported. Below Neutral-Ionic transition temperature, the ESE signals related to the spin solitons were observed. Comparing the phase memory time with the inverse of the EPR line-width, it was found that a crossover from fast motion of the spin solitons to slow motion took place around 70K. In addition ,the spin relaxation measurements suggested the thermal fluctuation of the dimerized lattice above 60K.

DOI： 10.1016/S0379-6779(98)00472-X

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(TTM-TTP)I-3 which has been considered as the typical one-dimensional half-filled band system, has been critically restudied by structural and magnetic measurements. X-ray diffuse scattering study reveals the formation of 2k(F) CDW superstructure with the wave vector q(1) =(0, 0, 0.5) below 160 K of the metal-insulator transition temperature. Another structural modulation with q(2) = (0.5, 0, 0.5) is observed below 90-100 K. modulated structure analysis using the q(2) satellite reflections and the Bragg reflections shows the large displacement in I-3 anion. Anomalies in chi line width and g-value of ESR measurements which correspond to the structural anomaly, are also reported.

DOI： 10.1016/S0379-6779(98)00473-1

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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].

DOI： 10.1103/PhysRevB.59.15062

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The annealing effects on the magnetic and structural properties for organic ferromagnet C-60 - TDAE are reported. The ESR line-width for unannealed single crystal shows a large hysteresis behavior around 130K. For the well-annealed crystal, on the other hand, the linewidth continuously changed with temperature. In addition, the room temperature structural analysis of the single crystal indicated that all the crystal axes, especially c-axis, shrunk after annealing.

DOI： 10.1016/S0379-6779(98)00702-4

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Ferromagnetic resonance (FMR) is used to measure the magnetic anisotropy field H-k and its dispersion of poly-crystalline recording media. This method does not use any single crystal substrate. A high-intensity field is applied vertically to a sample surface to completely saturate the magnetization and a high-frequency (over 50 GHz) magnetic field is applied in the surface. An FMR simulator based on the Landau-Lifshitz-Gilbert equation confirms that the magnetic (exchange and/or magnetostatic! interactions have very little effect on the resonant frequency in the configuration used. The linewidth of the FMR spectrum is affected by the H-k dispersion and damping constant. Methods using a torque or magnetization curve include magnetic interactions, resulting in a systematic error to the value of H-k. This FMR method is applied to CoCrPt-alloy thin-film media with a Cr-alloy underlayer grown on a glass substrate. A conventional torque method is also used for comparison. The axis of hexagonal-close-packed Co magnetic grain is distributed at random in the surface. In an FMR measurement, external magnetic field is applied vertically to the surface up to 55 kOe for two frequencies (71 and 117 GHz). The obtained H-k is 7.0+/-0.2 kOe, which is a little higher than the H-k of 6.4 kOe estimated with the torque loss method. Important physical parameters that affect the recording performance are also estimated using the linewidth of FMR spectra for different frequencies with a micromagnetic simulation: H-k dispersion=1.2+/-0.5kOe, Gilbert's damping constant alpha=0.03+/-0.01, and a g value=2.19+/-0.02. (C) 1999 American Institute of Physics. [S0021-8979(99)52108-7].

DOI： 10.1063/1.370459

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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 Delta approximate to 640 and 1080 GHz, respectively. When the external field is increased, the frequency of the lowest branch with the zero-field gap Delta approximate to 640 GHz decreases linearly with a tendency toward zero at H-c approximate to 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 Delta approximate to 160 GHz. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(97)00982-4

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We have performed ESR measurements on the S = 1/2 double-spin-chain systems KCuCl3 and TlCuCl3 using single crystals. The ground states of these compounds are spin singlet and there are finite gaps in their excitation spectra. The temperature dependence of the paramagnetic resonance intensity is similar to that of susceptibility. The direct transition from the singlet ground state to the excited triplet state is observed for both compounds. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(97)00442-3

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Submillimeter wave ESR measurements of the ABX(3) triangular antiferromagnet CsMnBr3 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 = 8.3K 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.

DOI： 10.1143/JPSJ.66.4017

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Magnetic properties of S = 1/2 double spin chain systems KCuCl3 and TlCuCl3 have been investigated by susceptibility, high-field magnetization process and ESR measurements using single crystals. The present systems can be described as a Heisenberg spin ladder with an additional interaction. It is found that the susceptibilities of both the compounds exhibit broad maxima and decrease exponentially to zero with decreasing temperature. This result indicates that the ground slate of the present system is a spin singlet and there is a finite gap in the excitation spectrum. The transition to the magnetic state is clearly observed by the high-field magnetization process. ESR absorption due to the excitation from the singlet ground state to the excited state is observed for TlCuCl3.

DOI： 10.1016/S0921-4526(97)00070-7

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Electron Spin Resonance (ESR) measurements have been performed on axial triangular antiferromagnets CsNiBr3 and CsMnI3 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 CsNiBr3 and CsMnI3 are determined.

DOI： 10.1143/JPSJ.65.1799

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The average magnetic moment per Fe atom for a single-phase, single-crystal Fe16N2(001) film epitaxially grown on a GaAs(001) substrate by molecular beam epitaxy has been confirmed to be 3.5 mu(B) at room temperature by using a vibrating sample magnetometer (VSM) and Rutherford backscattering. The value was in good agreement with that obtained by using a VSM and by measuring the film thickness (3.3 mu(B) per Fe atom). The saturation magnetization 4 pi M(s) has been found to increase with decreasing temperature, obeying T-3/2 law at lower temperatures. The slope was steeper than that of a pure Fe film, suggesting a lower exchange constant for Fe16N2. The g factor for Fe16N2 has been accurately measured to be 2.17 by using ferromagnetic resonance with changing frequencies of 35.5-115 GHz, which is not unusual compared with the g factor of 2.16 for pure Fe. The resistivity for Fe16N2 has been measured to be around 30 mu Omega cm at room temperature compared with 10 mu Omega cm for pure Fe and decreases linearly with decreasing temperature. The behavior was that for normal metal and nothing unusual was seen. The anomalous Hall resistivity for Fe16N2 was 4X10(-7) V cm/A, which is about three times as large as that for pure Fe. The relationship between the giant magnetic moment and the anomalous Hall resistivity has been clarified yet. (C) American Institute of Physics.

DOI： 10.1063/1.362246

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Antiferromagnetic resonances (AFMR) of a quasi-one-dimensional antiferromagnet (CH3)(4)NMnBr3 (TMMB) have been studied in a wide frequency range. The frequency versus field relation shows a prominent deviation from the classical AFMR theory, which may be attributed to the one-dimensional quantum effect.

DOI： 10.1016/0304-8853(94)01168-0

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Magnetic resonance experiments of the S = 1 Haldane gap material (CH3)(4)NNi(NO2)(3) (TMNIN) have been performed in the frequency range 9-115GHz in magnetic fields up to 8 T. Resonance absorptions associated with the transitions between the ground state and the lowest excited state have been observed below about 5 K. The frequency vs. field relations of the resonances provide a gap parameter E(g) similar to 3 K.

DOI： 10.1016/0304-8853(94)01097-8

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We have performed magnetic resonance measurements on the Ising-like Heisenberg triangular antiferromagnet CsNiBr3 in the lowest ordered phase. Remarkable deviations from the conventional 6-sublattice model were observed for some ESR eigen modes. We show that these deviations are removed by introducing a diagonal interchain interaction. We also investigate the exchange and anisotropy parameters of this compound.

DOI： 10.1016/0304-8853(94)01224-5

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The effect of the diagonal interchain exchange coupling J(2) on the ESR mode for hexagonal ABX(3) antiferromagnets is investigated. It is shown that the J(2) coupling is essential to describe the ESR results which cannot be explained by the conventional model including consistency with the static properties and spin wave excitations.

DOI： 10.1016/0304-8853(94)01009-9

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The temperature variations of the ESR spectrum of the triangular antiferromagnet CsNiCl3 over all three phases in a wide frequency range 9-115 GHz in magnetic fields up to 8 T have been studied. They are strongly dependent on the resonance modes and the applied fields (or frequencies), and are related to the magnetic ordering process.

DOI： 10.1016/0304-8853(94)01220-2

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   Publisher：The Surface Science Society of Japan  

Field-effect carrier doping to organic molecular solids is discussed from view of organic transistor application and modification of physical properties. The organic field-effect transistors with high k gate dielectric and electric double layer capacitor (EDL) are investigated, and the low-voltage operation is realized at present stage. Furthermore, the trap states are fully discussed because carriers accumulated by electric-field first occupy the trap states. In this report, we show the future prospective for modification of physical properties of organic solids.

DOI： 10.1380/jsssj.32.27

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Interference between intermolecular electronic oscillation (period; 18 fs) and intramolecular vibration (22 fs) shows that excited state is initially dressed by the C=C vibration during the photoinduced insulator to metal transition in layered organic salt. © OSA/UP 2010.

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