Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 74, Issue 8
Displaying 1-49 of 49 articles from this issue
  • Hiroyasu Ejiri
    2005 Volume 74 Issue 8 Pages 2101-2127
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    Neutrino-less double beta decays (0νββ), which violate the lepton number conservation law by ΔL=2, are of great interest for studying the fundamental properties of neutrinos beyond the standard electroweak theory. High-sensitivity 0νββ studies with mass sensitivities of the solar and atmospheric ν-masses are crucial for studying the Majorana nature of ν’s, the ν mass spectrum, the absolute ν-mass scale, the Majorana CP phases and other fundamental properties of neutrinos and weak interactions. Actually, high-sensitivity experiments of 0νββ are the unique and practical method for studying all these fundamental properties of neutrinos in the foreseeable future. On the basis of the recent ν oscillation studies, the effective mass sensitivity required for observing the 0νββ rate is of the order of the atmospheric ν mass scale of δmA∼50 meV in the case of the inverted mass hierarchy and of the order of the solar ν mass scale of δmS∼8 meV in the case of the normal hierarchy. The present ββ detectors with sensitivities of 150–300 meV are effective in the case of the quasi-degenerate ν mass spectrum. Future detectors with higher sensitivities of the orders of δmA–δmS, using different nuclei and methods (calorimetric, spectroscopic), are indispensable for establishing 0νββ. Theoretical and experimental studies for evaluating nuclear matrix elements M within 20–30% are important for extracting the sensible ν mass from the 0νββ rate. Charge exchange reactions by means of nuclear, electron and ν probes provide useful data for M. International collaboration for experimental and theoretical ββ works are encouraged to perform next-generation ββ experiments. High-sensitivity ββ detectors can be used for studying rare nuclear processes such as solar ν’s, dark matter, charge nonconservation, and nucleon decays. This report is a brief review of double beta decays and neutrinos with emphasis on high-sensitivity 0νββ studies for the Majorana ν mass.
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  • Miki Matsuo
    2005 Volume 74 Issue 8 Pages 2128-2132
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The relationship between correlation and response in the glass state of a binary lattice gas model is explored. In contrast to the Cugliandolo–Kurchan off-equilibrium fluctuation dissipation relation (FDR), we see a violation of the FDR. This collapse of the relation appears for a collective motion among particles of the glassy system. This violation of FDR is related to the inevitable irreversibility that accompanies a quasi-static operation applied to a glassy system.
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  • Yoshiyuki Kabashima
    2005 Volume 74 Issue 8 Pages 2133-2136
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    A scheme to provide various mean-field-type approximation algorithms is presented by employing the Bethe free energy formalism to a family of replicated systems in conjunction with analytical continuation with respect to the number of replicas. In the scheme, survey propagation (SP), which is an efficient algorithm developed recently for analyzing the microscopic properties of glassy states for a fixed sample of disordered systems, can be reproduced by assuming the simplest replica symmetry on stationary points of the replicated Bethe free energy. Belief propagation and generalized SP can also be offered in the identical framework under assumptions of the highest and broken replica symmetries, respectively.
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  • Kenichi Kato, Masaki Takata, Eiji Nishibori, Makoto Sakata, Noriaki Ha ...
    2005 Volume 74 Issue 8 Pages 2137-2140
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The charge density distribution of Nd0.35Sr0.65MnO3 has been investigated by means of the maximum entropy method (MEM) using the synchrotron radiation (SR) X-ray powder diffraction data. In this compound, the anisotropic optical spectra reported by Tobe et al. [Phys. Rev. B 67 (2003) 140402(R)] suggest that the d3z2r2 orbital-ordering survives even at 600 K (>>TN=260 K). Consistently, we observed an anisotropic charge density distribution around the Mn ion at 30 K (<<TN), indicating the long-range ordering of the d3z2r2 orbital. At 300 K (≥TN), however, the charge density distribution becomes isotropic, suggesting the disappearance of the long-range orbital ordering.
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  • Masahito Yoshizawa, Yoshiki Nakanishi, Masafumi Oikawa, Chihiro Sekine ...
    2005 Volume 74 Issue 8 Pages 2141-2144
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We have studied the origin of the successive phase transitions in filled skutterudite SmRu4P12 based on the results of elastic constant measurements. The temperature dependence of the elastic constants shows a sharp drop at the metal–insulator (M–I) transition of TMI=16.5 K in a zero field. The successive transition at TN=14 K is indistinct in a low field. The anomaly at TMI disappears with increasing field. A clear softening toward TN appears in the elastic constants in a high magnetic field. This result suggests a breakdown of the time reversal symmetry in the temperature range between TMI and TN. Such a breakdown is considered to be due to the coupling between the dipole moment and the octupole moment, which is allowed only in Th symmetry.
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  • Kazunori Umeo, Marcos A. Avila, Takeaki Sakata, Kouichirou Suekuni, To ...
    2005 Volume 74 Issue 8 Pages 2145-2148
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We report the thermal conductivity κ and specific heat C measurements down to 0.3 K on single-crystalline samples of n-type Sr8Ga16Ge30 and p-type Ba8Ga16Ge30 clathrates. The overall temperature dependence of κ(T) of both samples with a plateau at about 20 K and a quadratic T dependence below 1 K is well described by the soft-potential model. Using the soft-potential parameter of 4.4 K derived from the analysis of κ(T) for Sr8Ga16Ge30, the broad maximum of CT3 centered at 7 K is also well reproduced. The density of states of quasilocalized vibrational modes for Sr atoms in Sr8Ga16Ge30 has a maximum at 0.7 THz, in agreement with the low-energy peak in a previous Raman scattering study.
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  • Dai Aoki, Hiroshi Yamagami, Yoshiya Homma, Yoshinobu Shiokawa, Etsuji ...
    2005 Volume 74 Issue 8 Pages 2149-2152
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We succeeded in growing a high-quality single crystal of an enhanced Pauli paramagnet, NpGe3, by the Bi-flux method, and observed the de Haas–van Alphen (dHvA) effect. The topology of a Fermi surface is well explained by the relativistic linear augmented-plane-wave (LAPW) band calculations based on the 5f itinerant band model. The Fermi surface consists of a nearly spherical electron-Fermi surface with necks along the ⟨100⟩ direction, forming a hollow ball, centered at the R point, which is derived from the single band. The cyclotron effective mass is in the range from 2.6 to 16m0, which is enhanced approximately 3.5 times from the corresponding band mass.
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  • Yu Zhong Zhang, Peter Fulde, Peter Thalmeier, Alexander Yaresko
    2005 Volume 74 Issue 8 Pages 2153-2156
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We develop a microscopic theory for the charge ordering (CO) transitions in the spinels AlV2O4 and LiV2O4 (under pressure). The high degeneracy of CO states is lifted by a coupling to the rhombohedral lattice deformations which favors a transition to a CO state with inequivalent V(1) and V(2) sites forming Kagomé and trigonal planes, respectively. We construct an extended Hubbard-type model including a deformation potential which is treated in an unrestricted Hartree–Fock approximation and describes correctly the observed first-order CO transition. We also discuss the influence of associated orbital order. Furthermore, we suggest that due to different band fillings AlV2O4 should remain metallic while LiV2O4 under pressure should become a semiconductor when charge disproportionation sets in.
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  • Hiroaki Kusunose
    2005 Volume 74 Issue 8 Pages 2157-2160
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    A criterion for effective irrelevancy of the spin–orbit coupling in heavy-fermion superconductivity is discussed on the basis of the impurity Anderson model with two sets of Kramers doublets. Using Wilson’s numerical renormalization-group method, we demonstrate a formation of the quasi-particle as well as the renormalization of the rotational symmetry-breaking interaction in the lower Kramers doublet (quasi-spin) space. A comparison with the quasi-spin conserving interaction exhibits the effective irrelevancy of the rotational symmetry-breaking interaction for the splitting of two doublets Δ larger than the characteristic energy of the local spin fluctuation TK. The relevance to lattice models is briefly discussed.
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  • Keiji Yada, Hiroshi Kontani
    2005 Volume 74 Issue 8 Pages 2161-2164
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We analyze the normal electronic states of Na0.35CoO2 based on the effective dp model with a full d-orbital freedom using the fluctuation-exchange (FLEX) approximation. The electronic states sensitively depend on the topology of Fermi surfaces, which changes with the crystalline electric splitting (CES) due to the trigonal deformation. We succeed in reproducing the weak pseudogap behaviors in the density of states (DOS) and in the uniform magnetic susceptibility below 300 K, assuming that six small hole pockets predicted by LDA band calculations are absent. If these pockets exist, on the contrary, “anti-pseudogap behaviors” should inevitably appear. Thus, the present study strongly supports the absence of the small hole pockets in Na0.35CoO2, as reported by recent ARPES measurements. A large Fermi surface around the Γ-point would account for the superconductivity in water-intercalated samples.
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  • Yoichi Okimoto, Reiji Kumai, Sachio Horiuchi, Hiroshi Okamoto, Yoshino ...
    2005 Volume 74 Issue 8 Pages 2165-2168
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The neutral–ionic (N–I) phase transitions of the molecular valence state have been investigated by Raman spectroscopy and x-ray diffraction for a series of isostructural charge-transfer complexes, 4,4′-dimethyltetrathiafulvalene-p-chloranil (DMTTF-QCl4) and Br-substituted analogs DMTTF-QBrnCl4−n, in which the N–I transition temperature can be critically controlled with n. The anomalously broadened Raman spectrum of the valence-probing molecular vibration as well as the diffuse x-ray scattering of the ionic superlattice is observed ubiquitously around the N–I phase boundary, including the vicinity of the quantum critical (0 K-transition) point. The results quantify the quantum fluctuation between the two states of matter, van der Waals and ionic crystals.
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  • Ryuta Watanuki, Gou Sato, Kazuya Suzuki, Masaki Ishihara, Tatsuya Yana ...
    2005 Volume 74 Issue 8 Pages 2169-2172
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    Physical properties of DyB4 have been studied by magnetization, specific heat, and ultrasonic measurements. The magnetic entropy change and ultrasonic properties in intermediate phase II indicate that the degeneracy of internal degrees of freedom is not fully lifted in spite of the formation of magnetic order. The ultrasonic attenuation and huge softening of C44 in phase II suggest the existence of electric-quadrupolar (orbital) fluctuations of 4f-electrons. These unusual properties originate from a geometrical quadrupolar frustration.
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  • Hisashi Kotegawa, Hiroyuki Hidaka, Yoshiyuki Shimaoka, Takeshi Miki, T ...
    2005 Volume 74 Issue 8 Pages 2173-2176
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We report nuclear quadrupole resonance (NQR) measurement at ambient pressure and resistivity measurement under high pressure in the new heavy fermion (HF) compound SmOs4Sb12. The NQR spectrum and the nuclear spin–lattice relaxation rate (1⁄T1) clearly demonstrate the bulk nature of ferromagnetic ordering below TC∼2 K. The temperature dependence of 1⁄T1 exhibits the characteristic behaviors of a Kondo lattice. The application of pressure decreases Kondo temperature and stabilizes the magnetic ordering, which is the same tendency as that found in some Yb-based compounds. The obtained phase diagram indicates SmOs4Sb12 to be in the vicinity of its ferromagnetic critical point.
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  • Yoshihiko Ihara, Kenji Ishida, Kazuyoshi Yoshimura, Kazunori Takada, T ...
    2005 Volume 74 Issue 8 Pages 2177-2180
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    An 17O NMR measurement was performed on nonoriented polycrystalline Na0.35CoO2·yH2O with superconducting (SC) transition temperature Tc=4.6 K. A weak temperature dependence was observed in the Knight shift at the O site (17K). The spin part of 17K (17Kspin) is estimated from the plot of 17K against bulk susceptibility χ. The 17Kspin decreases in the SC state, indicative of the decrease in the in-plane component of the spin susceptibility. The nuclear spin–lattice relaxation rate 1⁄T1 at the O site 17(1⁄T1) shows a good scaling with 1⁄T1 at the Co site 59(1⁄T1). This indicates that the spin fluctuations at the O site originate from the Co spin dynamics. The relationships between 17(1⁄T1T) and 17Kspin and between 17(1⁄T1T) and 59(1⁄T1T) show the development of incommensurate fluctuations at q0 other than q=0 below 30 K. A clear indication of ferromagnetic correlations at q=0 was not observed from the present 17O NMR studies.
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  • Hiroto Adachi, Masanori Ichioka, Kazushige Machida
    2005 Volume 74 Issue 8 Pages 2181-2184
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    Effects of Pauli paramagnetism on thermodynamic quantities in a vortex state, such as the specific heat C and magnetization M, are studied using the quasiclassical Eilenberger formalism. We demonstrate that with an increase of paramagnetic depairing effect, the sigh of the curvature of the field dependence of C changes from negative to positive, and that the Maki parameter κ2 becomes an increasing function of temperature. Our results provide a natural explanation for the unusual field dependence of C seen in CeCoIn5 in terms of the paramagnetic effect.
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  • Tomoyuki Sasaki, Masaichiro Mizumaki, Kenichi Kato, Yasuo Watabe, Yosh ...
    2005 Volume 74 Issue 8 Pages 2185-2188
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    Here, we report on the direct observation of lattice distortion in the new quasi-one-dimensional spin system TiOBr by X-ray diffraction experiment using synchrotoron radiation. By comparing the crystal structure between TiOBr and TiOCl, the difference in b-axis length was considered to play a key role in determining the physical properties of both systems. Using a single crystal sample of TiOBr, superlattice reflections were observed at (0,1.5,0) and (0,2.5,0). The temperature dependence of the superlattice reflections implied the first-order transition at Tc1=27 K. We discussed the phase transition and analyzed the data using a simple dimerization model.
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  • Naofumi Aso, Hiroshi Kageyama, Katsuyuki Nukui, Masakazu Nishi, Hiroak ...
    2005 Volume 74 Issue 8 Pages 2189-2192
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    In this letter we report on the high energy-resolution neutron scattering studies on the dynamic structure factor of the two-triplet bound states in the two-dimensional S=1⁄2 Shastry–Sutherland system, SrCu2(BO3)2, in the energy transfer range of 4 to 7 meV. In contrast to the earlier interpretation of the low energy-resolution results, these bound state excitations show hardly any dispersion, but do show a strong wave-vector-dependent structure factor. Although these findings are in overall agreement with the recent theoretical calculation of the 2-triplon dynamic structure factor by Knetter and Uhrig [Phys. Rev. Lett. 92 (2004) 027204], they also show distinct differences, which may be due to some symmetry-breaking terms in the Hamiltonian that are not included in the theory, such as the interdimer Dzyaloshinski–Moriya interactions recently discovered in this compound.
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  • Kazumasa Hattori, Kazumasa Miyake
    2005 Volume 74 Issue 8 Pages 2193-2196
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    Using the numerical renormalization group method, we investigate an extended Anderson model, in which correlated electrons with the Γ1 (singlet)–Γ4 (triplet) f2 crystalline-electric-field (CEF) configuration hybridize with conduction electrons of Γ7 (doublet) and Γ8 (quartet) under cubic Oh symmetry, from a strong spin–orbit interaction limit. For the case of the parameters relevant to PrFe4P12, the system is under competition between the CEF singlet fixed point and the multichannel Kondo non-Fermi liquid fixed point arising from the quadrupolar coupling between the impurity with pseudospin 1 and the conduction electron with pseudospin 3/2 . We consider that this result reveals the origin of the heaviness of the effective mass and non-Fermi liquid behavior of the Pr-based filled skutterudite compounds.
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  • H. Hiraka, T. Machi, N. Watanabe, Y. Itoh, M. Matsuda, K. Yamada
    2005 Volume 74 Issue 8 Pages 2197-2200
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The doping effect of magnetic impurities on the lightly hole-doped antiferromagnetic state was investigated by neutron diffraction techniques using single crystals of La1.99Sr0.01Cu1−yNiyO4 (0.01≤y≤0.10). Dilute Ni-doping between y=0.02 and 0.05 dramatically changes the Q-dependence of the antiferromagnetic Bragg intensity, corresponding to a switch of spin structure from the La2CuO4 type (Cu type) to the La2NiO4 type (Ni type) triggered by a spin rotation in CuO2 planes. Upon Ni-doping, the Néel temperature (TN) increases and rapidly approaches that of nondoped La2CuO4 in the Cu-type phase due to the strong localization of doped carriers, whereas TN gradually decreases in the Ni-type phase. More interestingly, between the Cu- and Ni-type structures, there exists an intermediate region where the spin direction is between those of Cu- and Ni-types. In this region, we found an unusual temperature dependence of magnetic intensities, which suggests a temperature dependence of the spin direction. These unusual behaviors are discussed in terms of doped carrier itinerancy.
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  • Yoshikazu Tanaka, Koichi Katsumata, Susumu Shimomura, Yoshichika Onuki
    2005 Volume 74 Issue 8 Pages 2201-2204
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    Results of non-resonant X-ray Bragg diffraction measurements in the phase II of CeB6 under an applied magnetic field, H, are reported. The intensity of the superlattice reflection (n⁄2,n⁄2,n⁄2) increases dramatically with H applied along the [111] axis, where n is odd. On the other hand, the superlattice intensity decreases with H along the [\\bar211] axis normal to the scattering vector. These behaviors of the superlattice intensity in H are explained qualitatively by the combined effects of the magnetic moments tending to align parallel to H and the spin orbit coupling which tends to align the extended wave function of the f electron normal to H. Using this relation, one can manipulate the multipole moments in rare-earth compounds by magnetic fields.
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  • Masahiro Matsumura, Genki Hyoudou, Harukazu Kato, Takashi Nishioka, Ei ...
    2005 Volume 74 Issue 8 Pages 2205-2208
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We report a 121,123Sb nuclear quadrupole resonance (NQR) study of SrFe4Sb12 and BaFe4Sb12. The absence of hyperfine splitting or marked broadening in NQR spectra even at the lowest temperature (1.5 K) suggests the absence of uniform ferromagnetic ordering in both compounds. The nuclear spin-lattice relaxation rate divided by temperature, 1⁄T1T, does not follow the Korringa law, but shows a broad maximum at around 60 K. At temperatures higher than 80 K, 1⁄T1T can be decomposed into two terms, (1⁄T1T)0=const. and T-dependent (1⁄T1T)spin. The component (1⁄T1T)spin is proportional to χspin, which suggests that the present system is close to ferromagnetic instability, whereas below 60 K, (1⁄T1T)spin decreases to zero, being unexpected in typical nearly or weakly ferromagnetism.
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  • Satoru Saitoh, Shigeru Takagi, Makoto Yokoyama, Hiroshi Amitsuka
    2005 Volume 74 Issue 8 Pages 2209-2213
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The still unclarified hidden order phase below T0=17.5 K in the heavy-electron system URu2Si2 has been studied by 101Ru NQR on a single crystal under Hext=0 and ambient P. Considering an invariant form of the quadrupole coupling between a 101Ru nucleus and U 5f electrons, which is compatible with the symmetry of the U–Ru bonds, it is shown that U 5f quadrupoles can be probed by 101Ru NQR and that the singlet ground-state models for the (5f)2 configuration of U can naturally explain the observed large T-dependence of the NQR frequency 101ν2Q(T) above T0. 101ν2Q(T) shows a slight but significant increase below TQ≅13.5 K. Combining with general considerations on the effects on 101Ru NQR of a possible symmetry-breaking electric field gradient (EFG) or hyperfine field due to hidden order, we discuss that the increase can be interpreted as arising from symmetry-breaking EFG components of Vyz and/or Vzx due to quadrupole order. In this interpretation the onset of the quadrupole order is retarded by about 4 K below T0, which is discussed in connection with related measurements.
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  • Tomoyuki Mochida, Kousuke Takazawa, Masashi Takahashi, Masuo Takeda, Y ...
    2005 Volume 74 Issue 8 Pages 2214-2216
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    An “ionic(I)–ionic(II)” charge-transfer transition has been observed in a new molecular solid composed of dineopentylbiferrocene (D) and fluorotetracyanoquinodimethane (A). The material is a monovalent solid (D+A3) at room temperature and changes to a divalent solid (D2+A32−) at low temperatures, in association with a broad first-order phase transition at around 120 K.
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  • Jinbing Chen, Xianguo Geng
    2005 Volume 74 Issue 8 Pages 2217-2222
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The modified Kadomtsev–Petviashvili (mKP) equation is split into two soliton equations in the modified Jaulent–Miodek (mJM) hierarchy, and further into integrable finite-dimensional Hamiltonian systems (FDHSs) using the nonlinearization of Lax pairs. The Abel–Jacobi coordinate is introduced to linearize the mKP flow such that its solution is reduced as a linear superposition, expressed in the Abel–Jacobi variable. Finally, the algebro-geometric solution of the mKP equation is given via the Jacobi inversion.
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  • Dan Tanaka
    2005 Volume 74 Issue 8 Pages 2223-2225
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    First, we confirm that the chaos in the Kuramoto–Sivashinsky equation occurs through period-doubling cascade (Feigenbaum scenario). Then, we show that the chaos in the Nikolaevskii equation occurs via the torus-doubling bifurcation (Ruelle–Takens–Newhouse scenario).
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  • Kazuo Sasaki, Satoshi Amari
    2005 Volume 74 Issue 8 Pages 2226-2232
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The Brownian motion of a particle in a one-dimensional periodic potential subjected to a uniform external force F is studied. Using the formula for the diffusion coefficient D obtained by other authors and an alternative one derived from the Smoluchowski equation in the present work, D is compared with the differential mobility μ=dvdF where v is the average velocity of the particle. Analytical and numerical calculations indicate that inequality D≥μkBT, with kB the Boltzmann constant and T the temperature, holds if the periodic potential is symmetric, while it is violated for asymmetric potentials when F is small but nonzero.
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  • Shinsuke Uda, Yoshiyuki Kabashima
    2005 Volume 74 Issue 8 Pages 2233-2242
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The demand for extracting rules from high dimensional real world data is increasing in various fields. However, the possible redundancy of such data sometimes makes it difficult to obtain a good generalization ability for novel samples. To resolve this problem, we provide a scheme that reduces the effective dimensions of data by pruning redundant components for bicategorical classification based on the Bayesian framework. First, the potential of the proposed method is confirmed in ideal situations using the replica method. Unfortunately, performing the scheme exactly is computationally difficult. So, we next develop a tractable approximation algorithm, which turns out to offer nearly optimal performance in ideal cases when the system size is large. Finally, the efficacy of the developed classifier is experimentally examined for a real world problem of colon cancer classification, which shows that the developed method can be practically useful.
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  • Yositake Takane, Takahiro Murakami
    2005 Volume 74 Issue 8 Pages 2243-2248
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The pulse control of dephasing is studied for a two-level quantum system (qubit) interacting with a quantum environment. It has been shown that dephasing in a qubit due to qubit–environment interactions can be suppressed by a sequence of periodic π pulses with infinitely short duration. To study how the effectiveness of the pulse control is affected by finite pulse duration td, we calculate the time evolution of the reduced density operator for a qubit under a sequence of π pulses. We show that the pulse control is effective even for not short td if a suitable pulse sequence is adopted.
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  • C. Yubero, M. D. Calzada, M. C. Garcia
    2005 Volume 74 Issue 8 Pages 2249-2254
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    For a microwave plasma at atmospheric pressure the use of the Stark broadening of the Hα, Hβ and Hγ lines to determine the electron density and temperature is reported. Knowing the values of these plasma parameters is important because the electrons (density) and their energy (temperature) control the internal kinetics in the discharge. We found that the use of the Gigosos–Cardeñoso model permitted us to obtain the same value of the electron density from the Stark broadening of the three Balmer lines. The dependence of the Stark broadening on the electron density and temperature for Hα, Hβ and Hγ lines has permitted the application of an intersection method to try finding the values of the electron density and temperature simultaneously. The results have shown the possibility of estimating the electron density with an uncertainty of under 10% by using this intersection method, without knowing the accurate value of the electron temperature. In the case of the electron temperature the uncertainty was 40%, which seems to indicate that this method is not appropriate for the determination of this plasma parameter.
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  • Pawan K. Tiwari, G. J. H. Brussaard, M. J. v. d. Wiel, V. K. Tripathi
    2005 Volume 74 Issue 8 Pages 2255-2259
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    An indigenously built Ti:sapphire laser system delivering 50 mJ, 100 fs pulses at a repetition rate of 10 Hz, is employed to tunnel ionize air at 1 atm pressure and form a plasma channel. The laser is line focused using a cylindrical lens to a spot size of 20μm×1mm. A folded wave interferometry is used to deduce the radial electron density profile by measuring the phase shift and employing Abel inversion. The maximum value of chord-integrated electron density and radial electron density are estimated to be approximately equal to 3.0×1016 cm−2 and 4.0×1018 cm−3 respectively with density scale length of 20 μm. These results have been theoretically interpreted by developing a unified formalism of tunnel ionization. The experimental results are in reasonable agreement with the theory.
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  • Michiko Yamana, Masato Okada
    2005 Volume 74 Issue 8 Pages 2260-2264
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    There is growing interest in a phenomenon called the “synfire chain”, in which firings of neurons propagate from pool to pool in the chain. The mechanism of the synfire chain has been analyzed by many researchers. Keeping the synfire chain phenomenon in mind, we investigate a layered associative memory neural network model, in which patterns are embedded in connections between neurons. In this model, we also include uniform noise in connections, which induces common input in the next layer. Such common input in layers generate correlated firings of neurons. We theoretically obtain the evolution of retrieval states in the case of infinite pattern loading. We find a break down of self-averaging property, that is, the overlap between patterns and neuronal states is not given as a deterministic quantity, but is described by a probability distribution defined over the ensemble of synaptic matrices. Our simulation results are in excellent agreement with theoretical calculations.
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  • Hiroaki Ogawa, Michisuke Kobayashi, Tomohiro Iseki, Masaru Aniya
    2005 Volume 74 Issue 8 Pages 2265-2269
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The longitudinal and transverse collective modes are studied in liquid silver chalcogenides by making use of a hydrodynamic description. The effect of deviation from the stoichiometric composition is studied over a wide range of concentrations. The result reveals the existence of coupled collective modes. It is shown that the frequency gap at the crossing point of the modes decreases with the decrease in the relaxation time. An approximate analytical solutions for both, longitudinal and transverse modes are obtained. It is also shown that the analytical solutions for large value of the deviation from stoichiometry agree with the exact numerical solution.
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  • Akiko Harada, Fuyuki Shimojo, Kozo Hoshino
    2005 Volume 74 Issue 8 Pages 2270-2276
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We have carried out ab initio molecular-dynamics simulations for the model system of hydrogen-adsorbed graphite to investigate the temperature-induced desorption of hydrogen atoms from the graphite and found for the first time by the ab initio electronic structure calculations the desorption of hydrogen atoms as a hydrogen dimer, which moves almost freely between graphite layers. We have also investigated the microscopic mechanism of the desorption and the dimerization of the hydrogen atoms based on the electron density distribution as well as the overlap population analysis, and clarified that the dimerization occurs through the intermediate ‘bridge’ state such as –C–H–H–C–. Considering the increase in the temperature due to the recrystallization occurred in the nanostructured graphite, our results are consistent with the experimental results, in the sense that the recrystallization of the nanostructured graphite is necessary for the desorption of hydrogen atoms observed experimentally at higher temperature.
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  • Shugo Ikeda, Tatsuma D. Matsuda, Yoshinori Haga, Etsuji Yamamoto, Miho ...
    2005 Volume 74 Issue 8 Pages 2277-2281
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We have succeeded in growing a high-quality single crystal of an antiferromagnet UPdGa5 by the Ga-flux method with the off-stoichiometric composition of U:Pd:Ga=1:2:7.3. The Néel temperature TN=30.5 K is found to increase with increasing the residual resistivity ratio (RRR) and becomes constant for a high-quality single crystal sample whose RRR is larger than 50. The electronic state has been investigated by the de Haas–van Alphen experiment, indicating the similar cylindrical Fermi surfaces as in an antiferromagnet UPtGa5. We have also studied the pressure effect by measuring the electrical resistivity. The Néel temperature decreases with increasing pressure and becomes zero at 3.1 GPa. The antiferromagnetic state is changed into the paramagnetic state above 3.1 GPa.
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  • Hiroyuki Kimura, Yukio Noda, Futami Sato, Kenji Tsuda, Kenji Kurahashi ...
    2005 Volume 74 Issue 8 Pages 2282-2286
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    X-ray diffraction measurements have been performed to investigate a crystal structure of a precipitation phase in oxygen-reduced Nd1.85Ce0.15CuO4+y (NCCO). A detailed structure analysis of the precipitation phase as well as the parent NCCO phase revealed that the precipitation phase is a cubic (Nd,Ce)2O3, which is distorted tetragonally by the surrounding NCCO phase. The averaged grain size of the precipitation phase exceeds 200 Å parallel to the CuO2 plane of the parent NCCO, while the size along layered direction is short-ranged (∼30 Å). The grain thickness along layered direction is strongly correlated with the homogeneity of superconducting state. The volume fraction of the (Nd,Ce)2O3 phase is about 2%. We also performed electron diffraction as well as microscopy experiment, which confirms that the (Nd,Ce)2O3 phase segregate from the parent NCCO phase and exists as an epitaxial layer along the c-axis.
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  • Kiyoichiro Motoya, Keisuke Nakaguchi
    2005 Volume 74 Issue 8 Pages 2287-2293
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    Spin-wave excitations in reentrant spin-glass (RSG) materials have been a controversial issue for a long time. In one group of materials, spin-wave stiffness constant D and spin-wave amplitude As decrease as temperature decreases toward the spin-glass transition temperature in accordance with the decrease of magnetization. In another group of materials, the temperature variations of D and As are opposite to those observed in the former group. The coexistence of two kinds of spin-waves has been observed in the RSG alloy Fe65(Ni0.866Mn0.134)35. Temperature variations of D and As for each spin-wave are similar to those of each spin-wave observed in the two groups of materials. The origin of the two kinds of spin-wave excitations observed in different groups of RSG materials is attributed to the presence of spin-waves in finite-size magnetic clusters and in an infinite ferromagnetic network.
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  • Toshiaki Fujita, Shohei Kawabata, Masatoshi Sato, Nobuyuki Kurita, Mas ...
    2005 Volume 74 Issue 8 Pages 2294-2300
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    Transport, thermal, and magnetic measurements have been carried out on (Pr1−ySmy)1−xCaxCoO3. The system exhibits a structural phase transition accompanied by the spin state change from the intermediate spin (IS) state to the low spin (LS) state with decreasing temperature T. We have constructed a Ty phase diagram for x=0.3 and Tx ones for y=0.2 and 0.3. By analyzing their magnetic susceptibilities, the number of Co ions excited to the IS state (or the electron number in the eg orbitals), nIS, is roughly estimated. With increasing y or with decreasing x, nIS decreases, and the phase transition changes gradually to the (IS→LS) crossover-like one. We discuss the possible role of the Pr atoms in realizing the transition.
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  • Abdul Hannan, Daichi Kawana, Keitaro Kuwahara, Masahumi Kohgi, Yasuo N ...
    2005 Volume 74 Issue 8 Pages 2301-2309
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The magnetic structures of the low-carrier-system CeP are investigated under magnetic fields up to 12.5 T with the field H||[1\\bar10] and up to 14 T with H||[001] by synchrotron X-ray diffraction utilizing the unique relationship between the magnetic structure and lattice modulation in this system. The magnetic phases corresponding to the modulation wave vectors k=2⁄11, 2/10, 2/9 and 2/8 are observed at low temperatures. The magnetic phases with k=2⁄8 (↑↑°°°°°° or ↑↑←→←→←→), k=2⁄9 (↑↑°°°°°°° or ↑↑←→←→←→←) and k=2⁄11 (↑↑°°°°°°°°°) are the new phases under magnetic fields found in the present work. The result demonstrates that magnetic fields play a role similar to high pressure to realize the unique magnetic structure and its multistep change in CeP. This fact indicates the importance of the magnetic polaron effect mediated by the pf mixing effect in the system.
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  • Masashige Matsumoto, Manfred Sigrist
    2005 Volume 74 Issue 8 Pages 2310-2316
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    Magnetoelastic properties in field-induced magnetic ordered phases are studied theoretically based on a Ginzburg–Landau theory. A critical field for the field-induced ordered phase is obtained as a function of temperature and pressure, which determine the phase diagram. It is found that magnetic field dependence of elastic constant decreases discontinuously at the critical field, Hc, and that it decreases linearly with field in the ordered phase (H>Hc). We found an Ehrenfest relation between the field dependence of the elastic constant and the pressure dependence of critical field. Our theory provides the theoretical form for magnetoelastic properties in field- and pressure-induced ordered phases.
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  • C. H. Kim, K. H. Kim, S. H. Park, Hyun-jong Paik, J. H. Cho, Bog G. Ki ...
    2005 Volume 74 Issue 8 Pages 2317-2322
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We have studied the magnetic and thermal properties of Y substituted Ca3Co2O6. Ca3Co2O6 exhibits the ferrimagnetic ground state due to ferromagnetic intrachain coupling and antiferromagnetic interchain coupling. As Y substitution increases, which results in variation of the interaction strength of both interchain and intrachain coupling, gradual but unique changes of ground state from ferrimagnetic to nonmagnetic state have been observed in dc susceptibility, isothermal magnetization, heat capacity, and ac susceptibility. Y substitution induces site percolation on Co–O one-dimensional (1D) chain as well as Co two-dimensional (2D) triangular lattice, and site percolation as well as frustration explains experimental results of doped Co–O 1D chain system. The spin configuration of the Y substituted Ca3Co2O6 can be understood by using crystal field splitting model.
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  • Dai Aoki, Yoshiya Homma, Yoshinobu Shiokawa, Hironori Sakai, Etsuji Ya ...
    2005 Volume 74 Issue 8 Pages 2323-2331
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We grew high-quality single crystals of NpTGa5 (T=Fe, Rh, and Ni) with a tetragonal structure by the Ga-flux method and measured their electrical resistivity, specific heat, magnetic susceptibility, and magnetization. All the investigated compounds undergo magnetic ordering. NpFeGa5 orders antiferromagnetically at TN=118 K and shows another magnetic transition at T*=78 K. A relatively large electrical resistivity indicates that NpFeGa5 might be a low-carrier compound. NpRhGa5 also orders antiferromagnetically at TN1=36 K. Below another magnetic transition at TN2=32 K, the antiferromagnetic easy-axis is most likely changed from [001] to the (001) plane. On the other hand, NpNiGa5 undergoes ferromagnetic ordering at TC=30 K, where the magnetic moment of Np is directed along the [001] direction. Furthermore, below another magnetic transition at T*=18 K, the ordered moment is discontinuously enlarged and a change of the magnetic structure occurs. The electronic specific heat coefficients are approximately determined as 30, 52, and 100 mJ/K2·mol for NpFeGa5, NpRhGa5, and NpNiGa5, respectively. The magnetic susceptibility approximately follows the Curie–Weiss law at high temperatures (250<T<300 K) with effective magnetic moments ranging from 2.4 to 2.6 μB/Np for NpRhGa5 and NpNiGa5, indicating that the localized 5f4 electronic states are most likely applicable to these compounds at high temperatures.
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  • Tatsuya Kawae, Chenshu Li, Yasuo Yoshida, Kazuyoshi Takeda, Takayuki A ...
    2005 Volume 74 Issue 8 Pages 2332-2337
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The low-temperature properties of PrxLa1−xInAg2 have been studied for a wide concentration range of Pr ions between 0≤x≤0.6. The susceptibility above T=15 K is well reproduced by the crystal-electric-field level scheme with a non-Kramers Γ3 doublet in the ground state for each concentration, while that below T=15 K shows a non-Fermi-liquid behavior with a logarithmic temperature dependence. The temperature dependence of the specific heat CT shows a monotonic enhancement below T=10 K, which can be scaled by a characteristic temperature T* defined at each concentration. These results suggest that the anomalous low-temperature properties are understood as the single-ion nature of Γ3 quadrupolar moments. The origin of the anomalous properties is discussed in connection with the quadrupolar Kondo effect arising from the correlation between the Γ3 moments and the conduction electrons.
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  • Khian-Hooi Chew, Yoshihiro Ishibashi, Franklin G. Shin
    2005 Volume 74 Issue 8 Pages 2338-2346
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We present a detailed study of intrinsic ferroelectric hysteresis loops in a heterostructure of interface between two different ferroelectrics of the second-order transition by the Landau–Ginzburg theory. Our study indicates that the ferroelectric hysteresis behavior in an interfacial-coupled structure might be governed by the interplay of various parameters such as the interfacial coupling, the interaction between neighboring polarizations within the constituents and the dielectric softness of the constituents. Inhomogeneity of polarization at the interface induced by the interaction between the constituents across the interface assists the polarization reversal by reducing the coercive field of the heterostructures, implying an interface-aided polarization reversal. A significant reduction in the coercive field of the interface structure is expected to be possible if certain conditions based on the above-mentioned parameters are achieved.
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  • Dong-Seok Yang, Ikgyun Kim, Alexander N. Ulyanov, The-Long Phan, Seong ...
    2005 Volume 74 Issue 8 Pages 2347-2350
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    The local structure and electron configuration of Co and Fe ions in La0.5Sr0.5Co1−yFeyO3 (y=0.3 and 0.6) cobaltites have been examined by the X-ray absorption fine structure (XAFS) study. It was observed that the average valence of cobalt ions changed while the valence of iron ions did not. The average Fe–O bonding distance in (Fe/Co)O6 octahedra was higher than that of Co–O pairs. Based on the relationship between the Debye–Waller factor and bond strength, it was concluded that the strength of Co–O bond is stronger than that of Fe–O bond in the y=0.6 sample and weaker in the y=0.3 compound. The change of the Co-ion valence and the local structure of the perovskite cell with y are discussed in connection with the change of magnetic and transport properties of the cobaltites.
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  • T. Sasaki, N. Yoneyama, A. Suzuki, N. Kobayashi, Y. Ikemoto, H. Kimura
    2005 Volume 74 Issue 8 Pages 2351-2360
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    Systematic investigation of the electronic phase separation on macroscopic scale is reported in the organic Mott system κ-(BEDT-TTF)2Cu[N(CN)2]Br. Real space imaging of the phase separation is obtained by means of scanning micro-region infrared spectroscopy using the synchrotron radiation. The phase separation appears near the Mott boundary and changes its metal–insulator fraction with the substitution ratio x in κ-[(h-BEDT-TTF)1−x(d-BEDT-TTF)x]2Cu[N(CN)2]Br, of which band width is controlled by the substitution ratio x between the hydrogenated BEDT-TTF molecule (h-BEDT-TTF) and the deuterated one (d-BEDT-TTF). The phase separation phenomenon observed in this class of organics is considered on the basis of the strongly correlated electronic phase diagram with the first order Mott transition.
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  • Ryuichi Shindou, Naoto Nagaosa
    2005 Volume 74 Issue 8 Pages 2361-2373
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    We study the magneto-electric (ME) effect from the viewpoint of the Berry phase connection and quantum adiabatic charge transport. The linear response theory for the electronic polarization Pel can be interpreted in terms of the flux or the fictitious magnetic field related to the Berry phase in the generalized momentum space including external parameters. An applied magnetic field modifies the spin configuration, induces adiabatic deformation of the Bloch wavefunction, and results in the electronic polarization. This provides a new mechanism for the gigantic ME effect. For a cyclic change of the applied magnetic field, even a quantized charge transport is possible. We also argue how the so-called depolarization field affects this novel mechanism of ME effects, based on mean-field analyses.
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  • Thang Manh Hoang, Do Toan Minh, Masahiro Nakagawa
    2005 Volume 74 Issue 8 Pages 2374-2378
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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    In this paper, we investigate the synchronization scheme of two unidirectionally coupled multi-delay feedback chaotic systems in which the master drives the slave via a multi-delay driving signal. Moreover, the sufficient synchronization condition for the proposed scheme is determined by using the Krasovskii–Lyapunov theory. The effectiveness of the proposed synchronization scheme is verified and demonstrated by two specific examples. The simulation result illustrates that the drive system completely synchronizes with the response one via a multi-delay driving signal.
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  • Meng Wu, Xian-Wu Zou, Zhun-Zhi Jin
    2005 Volume 74 Issue 8 Pages 2379-2380
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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  • Masahito Mochizuki, Youichi Yanase, Masao Ogata
    2005 Volume 74 Issue 8 Pages 2381
    Published: August 15, 2005
    Released on J-STAGE: January 24, 2008
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