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Volume 77, Issue 12
Displaying 1-50 of 50 articles from this issue
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Sergei Sakovich2008 Volume 77 Issue 12 Pages 123001
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSUsing the Painlevé analysis preceded by appropriate transformations of nonlinear systems under investigation, we discover two new cases in which the Pietrzyk–Kanattšikov–Bandelow vector short pulse equation must be integrable due to the results of the Painlevé test. Those cases are technologically important because they correspond to the propagation of polarized ultra-short light pulses in usual isotropic silica optical fibers.View full abstractDownload PDF (89K) -
Takahiro Hatano2008 Volume 77 Issue 12 Pages 123002
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe rheological properties of a dense granular material consisting of frictionless spheres are investigated. It is found that shear stress, pressure, and kinetic temperature obey critical scaling near the jamming transition point, which is considered as a critical point. These scaling laws have some peculiar properties from the viewpoint of conventional critical phenomena because the exponents depend on the interparticle force model so that they are not universal. It is also found that these scaling laws imply the relation between the exponents that describe the growing correlation length.View full abstractDownload PDF (124K) -
Yuki Yanagi, Youichi Yamakawa, Yoshiaki Ono2008 Volume 77 Issue 12 Pages 123701
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe electronic states of the Fe2As2 plane in iron-based superconductors are investigated on the basis of the two-dimensional 16-band d–p model which includes the Coulomb interaction on a Fe site: the intra- and inter-orbital direct terms U and U′, the Hund’s coupling J and the pair-transfer J′. Using the random phase approximation (RPA), we obtain the magnetic phase diagram including the stripe and the incommensurate order on the U′–J plane. We also solve the superconducting gap equation within the RPA and find that, for large J, the most favorable pairing symmetry is extended s-wave whose order parameter changes its sign between the hole pockets and the electron pockets, while it is dxy-wave for small J.View full abstractDownload PDF (442K) -
Yutaka Itoh, Takao Mizoguchi, Kazuyoshi Yoshimura2008 Volume 77 Issue 12 Pages 123702
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe report a novel critical exponent δ≈3⁄2 of magnetization curves M∝H1⁄δ near the ferromagnetic quantum phase transitions of Sr1−xAxRuO3 (A = Ca, La0.5Na0.5, and La), which the mean field theory of the Ginzburg–Landau–Wilson type fails to reproduce. The effect of dirty ferromagnetic spin fluctuations might be the key to the small δ.View full abstractDownload PDF (397K) -
Kazumasa Miyake2008 Volume 77 Issue 12 Pages 123703
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe mechanism of incommensurate (IC) spin-density-wave (SDW) order observed in the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase of CeCoIn5 is discussed on the basis of new mode-coupling scheme among IC-SDW order, two superconducting orders of FFLO with B1g (dx2−y2) symmetry and π-pairing of odd-parity. Unlike the mode-coupling schemes proposed quite recently by Kenzelmann et al., that proposed in the present Letter can offer a simple explanation for why the IC-SDW order is observed only in FFLO phase and the IC wave vector is rather robust against the magnetic field.View full abstractDownload PDF (97K) -
Noriaki Kida, Yuichi Yamasaki, Ryo Shimano, Taka-hisa Arima, Yoshinori ...2008 Volume 77 Issue 12 Pages 123704
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSA broad continuum-like spin excitation (1–10 meV) with a peak structure around 2.4 meV has been observed in the ferroelectric ab spiral spin phase of Gd0.7Tb0.3MnO3 by using terahertz (THz) time-domain spectroscopy. Based on a complete set of light-polarization measurements, we identify the spin excitation active for the light E vector only along the a-axis, which grows in intensity with lowering temperature even from above the magnetic ordering temperature but disappears upon the transition to the A-type antiferromagnetic phase. Such an electric-dipole active spin excitation as observed at THz frequencies can be ascribed to the two-magnon excitation in terms of the unique polarization selection rule in a variety of the magnetically ordered phases.View full abstractDownload PDF (294K) -
Takahiro Fukui, Takanori Fujiwara, Yasuhiro Hatsugai2008 Volume 77 Issue 12 Pages 123705
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe show that the Z2 invariant, which classifies the topological properties of time reversal invariant insulators, has deep relationship with the global anomaly. Although the second Chern number is the basic topological invariant characterizing time reversal systems, we show that the relative phase between the Kramers doublet reduces the topological quantum number Z to Z2.View full abstractDownload PDF (104K) -
Tsuyoshi Miyazaki, David R. Bowler, Michael J. Gillan, Takahisa Ohno2008 Volume 77 Issue 12 Pages 123706
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSDensity functional theory (DFT) in a linear-scaling implementation is used to study the energetics of three-dimensional (3D) Ge islands (hut clusters) grown on Si(001) surface. DFT calculations on the fully relaxed energies of a series of hut clusters of increasing size are reported, finding a 2D to 3D cross-over near three monolayers; the number of atoms in the largest simulated system is over 20,000. A variety of technical issues which are important in addressing the accuracy and validity of the calculations are described and assessed. The results suggest that energetics alone is responsible for the initial transition from 2D to 3D growth.View full abstractDownload PDF (149K) -
Hiroaki Ikeda2008 Volume 77 Issue 12 Pages 123707
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe investigate interplay between magnetic fluctuations and superconductivity in the effective five-band Hubbard model for iron-oxypnictide superconductors on the basis of the fluctuation–exchange approximation. As for the normal-state properties, we find the pseudogap behavior in the NMR relaxation rate and the spectral weight in the electron-doped region, while we cannot find such behavior in the hole-doped region. The pseudogap behavior originates from the band structure effect, that is, existence of high density of states just below the Fermi level. Solving the superconducting Eliashberg equation, we find that the most probable candidate for the pairing symmetry is the sign-changed s-wave spin-singlet state. For small Hund’s coupling J, the eigenvalue is not so sensitive to carrier doping, and seems to be irrelevant with antiferromagnetic (AF) spin fluctuation. We suggest that correlation between spin and spin-quadrupole is important as the pairing mechanism as well as the AF fluctuation.View full abstractDownload PDF (700K) -
Hiroyasu Koizumi2008 Volume 77 Issue 12 Pages 123708
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe calculate the optical conductivity of the effectively half-filled Mott insulator that has been put forward as a relevant state for cuprates. It is shown that a Drude-like peak appears from transitions to spin-wave excited states that emerge when spin vortices exist; thus, it is indicated that the Drude-like peak in underdoped cuprates may not be a sign of the coherent motion of doped holes, but actually a sign of the presence of spin vortices and small polarons. The amplitude of the Drude-like peak increases with an increase in the number of spin vortices. Therefore, the doping and temperature dependences of the optical conductivity of cuprates are explained by the doping and temperature variations in the number of spin vortices. The calculated effective carrier number is also shown to explain the experimental value.View full abstractDownload PDF (997K) -
Eiji Kaneshita, Alan R. Bishop2008 Volume 77 Issue 12 Pages 123709
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe analyze pressure effects on stripe states within a selfconsistent Hartree–Fock calculation for a model of a striped nickelates. The results show a transition induced by high pressure and predict possible new spin states. We describe characteristics in the phonon excitations at the predicted transition, based on a real-space random phase approximation.View full abstractDownload PDF (754K) -
Gaku Motoyama, Nobuyuki Yokoyama, Akihiko Sumiyama, Yasukage Oda2008 Volume 77 Issue 12 Pages 123710
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe carried out simultaneous measurements of electrical resistivity and thermal expansion of the heavy-fermion compound URu2Si2 under pressure using a single crystal. We observed a phase transition anomaly between hidden (HO) and antiferromagnetic (AFM) ordered states at TM in the temperature dependence of both measurements. For the electrical resistivity, the anomaly at TM was very small compared with the distinct hump anomaly at the phase transition temperature T0 between the paramagnetic state (PM) and HO, and exhibited only a slight increase and decrease for the I||a-axis and c-axis, respectively. We estimated each excitation gap of HO, ΔHO, and AFM, ΔAFM, from the temperature dependence of electrical resistivity; ΔHO and ΔAFM have different pressure dependences from each other. On the other hand, the temperature dependence of thermal expansion exhibited a small anomaly at T0 and a large anomaly at TM. The pressure dependence of the phase boundaries of T0 and TM indicates that there is no critical end point and the two phase boundaries meet at the critical point.View full abstractDownload PDF (643K) -
Kenji Fujiwara, Yoshiki Hata, Keigo Kobayashi, Kiyotaka Miyoshi, Jun T ...2008 Volume 77 Issue 12 Pages 123711
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe report the results of 63Cu nuclear quadrupole resonance (NQR) measurements on CeCu2Si2 under high pressures up to 4.8 GPa. Enhanced spin fluctuations due to quantum criticality at ambient pressure are drastically suppressed with increasing pressure, whereas Tc increases from 0.7 K at ambient pressure to 1.64 K at 4.2 GPa. We have found that bulk superconductivity suddenly disappears at 4.8 GPa accompanied with a rapid decrease in the density of states at the Fermi level. The nuclear spin–lattice relaxation rate 1⁄T1 at 4.2 GPa reveals that anisotropic superconductivity in the strong-coupling regime is realized even under high pressure far from the antiferromagnetic critical point. Superconductivity under high pressure is unconventional in origin, but the spin fluctuation scenario is not likely to be applicable.View full abstractDownload PDF (156K) -
Shunsuke Furukawa, Masahiro Sato, Yasuhiro Saiga, Shigeki Onoda2008 Volume 77 Issue 12 Pages 123712
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe present a quantum theory for one-dimensional spin-1/2 multiferroics, where the vector spin chirality couples with the electric polarization. Based on exact diagonalization and bosonization, it is shown that quantum fluctuations appreciably reduce the chiral ordering amplitude and the associated ferroelectric polarization. This yields nearly collinear spin correlations in short-range scales, in qualitative agreement with recent neutron scattering experiments. There appear gapless chirality excitations described by phasons and new solitons, which can be experimentally verified from the low-energy dielectric response.View full abstractDownload PDF (257K) -
Yutaka Itoh, Naofumi Moritsu, Kazuyoshi Yoshimura2008 Volume 77 Issue 12 Pages 123713
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe report 7Li NMR studies of V-substitution effects on the spinel oxide superconductor LiTi2O4 (Tc=13.4 K). In LiTi2−xVxO4 (x=0–0.4), the V substitution for the Ti site suppressed the relative volume fraction of superconductivity faster than Tc. From the observation of a fairly homogeneous increase in 7Li nuclear spin–lattice relaxation rate, we conclude that the V substitution changes electron correlation effects through electron carrier doping from quarter electron filling 3d0.5 to 3d1.5 and then the antiferromagnetic correlation emerges.View full abstractDownload PDF (211K) -
Ryosuke Yoshii, Mikio Eto2008 Volume 77 Issue 12 Pages 123714
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe Kondo effect is theoretically studied in a quantum dot embedded in an Aharonov–Bohm (AB) ring when the size of the ring is much smaller than the Kondo cloud. First, we construct an equivalent model in which a quantum dot is coupled to a single lead. The AB interference effect is involved in the magnetic-flux dependence of the density of states in the lead. The scaling analysis of this model yields analytical expressions for the Kondo temperature TK and conductance at temperatures T>>TK. We show that TK may be significantly modulated by the magnetic flux penetrating the ring. Our method is generally applicable to the investigation of the Kondo effect in mesoscopic complex systems including a quantum dot.View full abstractDownload PDF (112K) -
Sun Kyung Lee, Hai-Woong Lee2008 Volume 77 Issue 12 Pages 124001
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe investigate the origin of the resolution improvement beyond the classical diffraction limit in quantum lithography. We show that the degree of the resolution improvement persists even when the pure entangled state of light initially prepared (the NOON state) is transformed to a mixed entangled state caused by phase and amplitude damping, regardless of the degree of entanglement remaining in the state. We also show that the resolution improvement beyond the classical diffraction limit can be achieved with a particular class of separable states of light. The resolution improvement in this case can be traced to entanglement (of the NOON type) that may be considered to be embedded in the separable state. We conclude that it is the existence of entanglement (of the NOON type) in the state of light used, not details of entanglement such as the degree of entanglement and relative weight of entanglement in the state, that determines the degree of the resolution improvement in quantum lithography. The visibility of the pattern and the total deposition rate, however, depend on the details of entanglement.View full abstractDownload PDF (108K) -
Tomoyuki Kimoto, Tatsuya Uezu, Masato Okada2008 Volume 77 Issue 12 Pages 124002
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe study a neural network model for the inferior temporal cortex, in terms of finite memory loading and sparse coding. We show that an uncorrelated Hopfield-type attractor and some correlated attractors have multiple stability, and examine the retrieval dynamics for these attractors when the initial state is set to a noise-degraded memory pattern. Then, we show that there is a critical initial overlap: that is, the system converges to the correlated attractor when the noise level is large, and otherwise to the Hopfield-type attractor. Furthermore, we study the time course of the correlation between the correlated attractors in the retrieval dynamics. On the basis of these theoretical results, we resolve the controversy regarding previous physiologic experimental findings regarding neuron properties in the inferior temporal cortex and propose a new experimental paradigm.View full abstractDownload PDF (178K) -
Tetsu Yajima, Hideaki Ujino2008 Volume 77 Issue 12 Pages 124003
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSStochastic processes associated with traveling wave solutions of the sine-Gordon equation are presented. The structure of the forward Kolmogorov equation as a conservation law is essential in the construction of the stochastic process as well as the traveling wave structure. The derived stochastic processes are analyzed numerically. An interpretation of the behaviors of the stochastic processes is given in terms of the equation of motion.View full abstractDownload PDF (219K) -
Shigeru Taniguchi, Asami Iwasaki, Masaru Sugiyama2008 Volume 77 Issue 12 Pages 124004
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe relationship between Maxwell boundary condition used in kinetic theory and two kinds of stochastic thermal wall used in molecular dynamics simulations is studied analytically. It is proved that one of the thermal walls is equivalent to Maxwell boundary condition by the detailed analysis of mass, momentum and energy conservation laws at a boundary. A new thermal wall, which takes into account both the probability of the thermalization of an incident particle at a boundary and the motion of the wall, is proposed. As a typical example, a temperature jump at a boundary of a stationary one-dimensional system is also derived explicitly.View full abstractDownload PDF (99K) -
Takashi Mori, Seiji Miyashita2008 Volume 77 Issue 12 Pages 124005
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe study the structure of the time evolution of the density matrix in contact with a thermal bath in a standard projection operator scheme. In general, the equation of motions of the density matrix with dissipative effects tends to lead any initial state into a steady state. The reduced density matrix of the system in the steady state is obtained by tracing out the degree of freedom of the thermal bath from the density matrix for the equilibrium state of the total system. This reduced matrix is modified by the interaction, and is different from that of the equilibrium of the system alone. In a commonly used equation of motion of the reduced density matrix, we have three terms, i.e., a term of the quantum mechanical evolution of the system density matrix, a term of the non-Markov evolution due to memory effects, and a term depending on the initial total density matrix. We make clear roles of the three terms by explicit calculations of the contributions of the terms to the steady state density matrix. By making use of the role of each term, the properties of the commonly used quantum master equation are examined. For example, if we do not include the imaginary part of the second term, the quantum master equation leads the reduced density matrix into that of the equilibrium of the system without modification. On the other hand, if we include the imaginary part, the steady state density matrix of the system satisfies the master equation up to the second order of the interaction. This property indicates that, in the representation that diagonalizes the system Hamiltonian, the leading order (the second order) terms of the off-diagonal elements of the steady state solution of the master equation agree with those of the density matrix of the equilibrium state.View full abstractDownload PDF (146K) -
Romain Modeste Nguimdo, Samuel Noubissie, Paul Woafo2008 Volume 77 Issue 12 Pages 124006
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe study the amplification of a pulse soliton in a discrete nonlinear electrical transmission line using negative nonlinear resistances and inductances linearly varying in space. The numerical simulation is used to solve the resulting set of discrete nonlinear differential equations in each case. In both cases, the dissipative effects of the medium in which it travels are compensated on a short distance of a doped domain. During the crossing of this doped domain, the wave conserves its pulse form and recovers its amplitude when coming out.View full abstractDownload PDF (907K) -
Giovanni Fazio, Giorgio Giardina, Francis Hanappe, Giuseppe Mandaglio, ...2008 Volume 77 Issue 12 Pages 124201
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe influence of the orientation angles of the target nucleus symmetry axis, relative to the beam direction, on the production of the evaporation residues is investigated for the 48Ca+154Sm reaction as a function of beam energy. At low energies (Ec.m.<137 MeV), the yield of evaporation residues is observed only for collisions with small orientation angles (αT<45°). At large energies (about Ec.m.=140–180 MeV), all orientation angles αT can contribute to the evaporation residue cross section σER in the 10–100 mb range. At Ec.m.>180 MeV, σER ranges approximately 0.1–10 mb because the fission barrier for a compound nucleus decreases with increasing excitation energy and angular momentum.View full abstractDownload PDF (543K) -
Kyungsik Kim, Myung-Ki Cheoun, Byung Geel Yu2008 Volume 77 Issue 12 Pages 124202
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWithin the framework of a relativistic single particle model we calculate neutral- and charged-current reactions for the neutrino scattering on 12C and 16O in quasielastic region. In the intermediate neutrino energy (500 MeV), we develop several ways to investigate effects of the strangeness, such as ratios of proton to neutron for neutral-current reaction, ratios of the neutral- to charged-current reactions, and asymmetries by incident neutrino and antineutrino. A cancellation mechanism of the strangeness effects in the nuclei was found to lead to indiscernible strangeness effects on the relevant cross sections. Consequently, the strangeness effects on the asymmetries and ratios are more feasible tools of looking for the strangeness effects rather than those on the cross section. These phenomena are shown to be nearly independent of the target nuclei exploited in this calculation.View full abstractDownload PDF (173K) -
Wei-Guo Jin, Yoshikazu Nemoto, Hiroki Nakai, Masayuki Kawamura, Tatsuy ...2008 Volume 77 Issue 12 Pages 124301
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSHigh-resolution atomic-beam laser spectroscopy in Gd I and Er I has been performed in the ultraviolet (UV) region. Isotope shifts have been measured for three UV transitions in Gd I and two transitions in Er I. Hyperfine structure constants of 155,157Gd and 167Er have been newly determined for two high-lying levels. Specific mass shifts and field shifts have been derived for the 4f75d6s2–4f75d26p and 4f75d6s2–4f85d6s transitions in Gd I as well as the 4f126s2–4f115d6s2 and 4f126s2–4f115d26s transitions in Er I. Results show that the specific mass shift strongly depends on the orbital angular momentum of electrons.View full abstractDownload PDF (155K) -
Dae-Soung Kim, Fumihiro Koike2008 Volume 77 Issue 12 Pages 124302
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe report the theoretical photoionization cross sections in the low energy region for Mg-like Si2+ ion, with arousing desire for experiments. With the advent of third-generation synchrotron radiation sources, it is expected to study for this ionic system using merged-beam technique. Since the Mg-like Si2+ ions are expected to be admixed with the ground-state and several low-lying excited-states, we have calculated the photoionization cross sections from the initial ground-state 3s2 1S, and the excited-states 3s3p 1,3P, 3s3d 1,3D, and 3s4s 1,3S of Mg-like Si2+ ion. For these calculations, we have used a most elaborate noniterative eigenchannel R-matrix method. We briefly discuss the results for autoionizing resonances and interlopers in the structure of photoionization cross sections, and compare with the previous results of Opacity Project.View full abstractDownload PDF (1073K) -
Akira Narita2008 Volume 77 Issue 12 Pages 124303
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe exchange–correlation functional composed of the Xα-exchange energy and the new type of correlation energy EM is assumed in order to study the effect of the nonspherical spatial distribution of electrons and the degeneracy of the total energy for states with the different ML values in the electronic open-shell configuration lN (l=p,d) of atom, where N is the number of electrons in the open shell characterized by directional quantum number l, ML is an expectation value of the z-component Lz of total angular momentum, and EM depends on ML. Nonspherical quantities such as electron density and one-electron effective potential are made from the partially filled occupation obeying Hund’s first rule in the open shell, and the Kohn–Sham equation is solved by the self-consistent degenerate first-order perturbation theory. Then, the parameters included in EM are succinctly and conveniently determined by imposing the appropriate conditions of degeneracy on the orbital and total energies. These methods are applied to the first-row and 3d transition atoms. Numerically self-consistent results, in which the final occupied orbitals agree with the starting ones used for the construction of electron density, are obtained, and the energies are reasonably acceptable since the occupied orbitals are more low-lying than the empty ones. Furthermore, the degeneracy of total energy with respect to ML is also obtained.View full abstractDownload PDF (263K) -
Katsumi Ida, Shigeru Inagaki, Ryuichi Sakamoto, Kimitaka Itoh, Kenji T ...2008 Volume 77 Issue 12 Pages 124501
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSA second-order phase transition of heat transport, which is characterized by a discontinuity in the time derivative of the temperature gradient, is observed in the high temperature plasma when the radial heat flux is modulated by repetitive pellet injections. The temperature dependence of the heat flux changes at the phase transition between two transport branches: one has a strong temperature dependence as predicted by gyro-Bohm type transport and the other has a weak temperature dependence which is consistent with the transport with the “screened” effect of zonal flow.View full abstractDownload PDF (1373K) -
Yoichi Nishiwaki, Akira Oosawa, Tetsuya Kato, Takumi Hasegawa, Haruhik ...2008 Volume 77 Issue 12 Pages 124601
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe structural changes of TlCoCl3 around phase IV (68<T<75 K) were studied by single-crystal neutron diffraction measurement. The present investigation revealed that a small but definite Bragg peak at (1⁄6,1⁄6,2) appeared only in phase IV. A precursor phenomenon of the phase V (T<68 K) structure in the phase IV temperatures was also identified as the coexistence of a slightly broadened (1⁄4,1⁄4,2) Bragg peak. We confirmed that intermediate phase IV is a stable, nontransient, single phase with 2\\sqrt3a×2\\sqrt3a×c unit cells. A possible sequence of structural phase transitions was proposed.View full abstractDownload PDF (203K) -
Eiichi Yagi, Kiwamu Sakuma, Naota Higami, Shinichi Hagiwara, Katsuhito ...2008 Volume 77 Issue 12 Pages 124602
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe effect of ion-irradiation on the state of hydrogen in Nb doped with hydrogen of a concentration of [H]⁄[M]=0.023 (hydrogen-to-metal-atom ratio) from the gas phase has been investigated at room temperature by the channelling method utilizing a nuclear reaction 1H(11B,α)αα with a 11B beam of an energy of about 2 MeV. It has been demonstrated that, before irradiation, hydrogen is located at a tetrahedral (T) site, while, after irradiation at room temperature with the 11B beam in the off-channelling direction up to a dose of about 1.4×1016/cm2, hydrogen is displaced from a T site by 0.45–0.55 Å towards its nearest neighbour lattice point. It is concluded that this irradiation-induced site change of hydrogen is due to trapping of hydrogen by irradiation-introduced monovacancies. Hydrogen is located at a site displaced from one of the nearest neighbour T sites of a vacancy by 0.45–0.55 Å towards that vacancy.View full abstractDownload PDF (226K) -
Yuha Kobayashi, Takahiro Onimaru, Marcos A. Avila, Kenzo Sasai, Minoru ...2008 Volume 77 Issue 12 Pages 124701
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe Kondo lattice antiferromagnet YbNiSi3 was investigated by neutron scattering techniques. The magnetic structure of YbNiSi3 was determined by neutron diffraction techniques on a single-crystalline sample. We revealed that the magnetic moments of Yb atoms align along the b-axis and are composed a ferromagnetic bc plane stacking antiferromagnetically along the a-axis. Inelastic neutron scattering experiments were also performed on a pulverized sample to study the crystalline electric field (CEF) excitations. Two broad CEF excitations were observed, from which we propose a plausible CEF model. The temperature dependences of the magnetic susceptibility χ and the magnetic specific heat Cmag were calculated using the probable CEF parameters, and compared with previous results.View full abstractDownload PDF (843K) -
Masatoshi Toda, Hitoshi Sugawara, Ko-ichi Magishi, Takahito Saito, Kun ...2008 Volume 77 Issue 12 Pages 124702
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe have synthesized the polycrystalline samples of Ge-based filled skutterudites RPt4Ge12 (R=La, Ce, Pr, Nd) and investigated the lattice constant, electrical resistivity, magnetic susceptibility and nuclear magnetic resonance (NMR) systematically. LaPt4Ge12 is confirmed to be a conventional BCS-type superconductor by the NMR measurements. Additional contribution ascribed to the rattling motion of the La ions has been observed in the nuclear relaxation at the La site at high temperatures. Temperature dependence of the magnetic susceptibility of CePt4Ge12 shows a broad peak around 80 K, which is a typical feature of valence fluctuation systems, whereas PrPt4Ge12 and NdPt4Ge12 show the well-localized nature of 4f-electrons. The NMR measurements in CePt4Ge12 revealed that the nuclear spin–lattice relaxation rate 1⁄T1 shows an activation-type temperature dependence 1⁄T1∝exp(−Δ⁄kBT) with an energy gap Δ⁄kB=150 K above 100 K, whereas it is proportional to the temperature below 20 K. This behavior is explained by a pseudogap model originated by the c–f hybridization.View full abstractDownload PDF (639K) -
Keisuke Tomiyasu, Haruhiro Hiraka, Kenji Ohoyama, Kazuyoshi Yamada2008 Volume 77 Issue 12 Pages 124703
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe performed powder neutron scattering experiments on spinel ferrimagnets ACr2O4 with magnetic and Jahn–Teller A2+ ions (A = Fe, Ni, Cu). In both FeCr2O4 and NiCr2O4, although geometric frustration had been expected to vanish so far, resonance-like magnetic excitation modes were discovered around Q\\simeq1.4 Å−1 and E\\simeq5 and 8 to 9 meV in a low-temperature magnetic order phase, similar to the local spin resonance modes early reported in highly frustrated spinel antiferromagnets ACr2O4 with nonmagnetic and non-Jahn–Teller A2+ ions (A = Mg, Zn). In a high-temperature magnetic order phase the resonance-like inelastic scattering transformed into quasielastic scattering. In CuCr2O4 no such diffusive scattering was observed. We interpret the resonance-like magnetic excitations as a dynamical spin-frustration effect, and discuss a necessary condition for the appearance of them.View full abstractDownload PDF (287K) -
Chandrashekhar S. Garde, Tetsuya Takeuchi, Yasunori Nakano, Yuji Taked ...2008 Volume 77 Issue 12 Pages 124704
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSHigh-quality single crystals of R3Al11 (R=La, Ce, Pr, and Nd) with the La3Al11-type orthorhombic crystal structure (space group Immm) have been grown by the Al-flux method. For Ce3Al11, signatures for ferromagnetic and antiferromagnetic orderings at TC=6.3 K and TN=3.2 K, respectively, have been observed in the magnetic susceptibility, magnetization, specific heat, and electrical resistivity. An antiferromagnet Pr3Al11, on the other hand, exhibits two magnetic transitions at TN1=12.6 K and TN2=3.1 K. An antiferromagnet Nd3Al11 also exhibits multiple magnetic transitions at TN1=13.2 K, TN2=9.4 K, TN3=2.9 K, and TN4=1.77 K in zero magnetic field. The transition at TN4 has a first-order character. The crystalline electric field (CEF) analysis of magnetic susceptibility, magnetization and specific heat data shows that the CEF splitting is larger for Ce3Al11 than for Pr3Al11 and Nd3Al11. The CEF ground state of Pr3Al11 is a singlet. Magnetic order occurs in this compound owing to the exchange mixing of the CEF ground state and low-lying excited states. The ferromagnetic like component of the magnetization for H||[010] is characteristic of R3Al11 (R=Ce, Pr, and Nd), which is most likely due to the Dzialoshinsky–Moriya interaction for two nonequivalent R atoms.View full abstractDownload PDF (3239K) -
Limin Wang, Weiyi Zhang, Zhenxing Liu2008 Volume 77 Issue 12 Pages 124705
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe two-band Anderson lattice model is a minimum model for compounds where the bands near the Fermi energy arise from the hybridization among different atoms. In the presence of site-selective disorder via atomic doping, we show by using the standard transfer matrix method that a unique type of critical state appears at the edge of a less disorder-affected band but with strong van Hove singularity, the asymptotic localization length λM neither depends on the lateral size M nor the disorder strength W. λM is five orders of magnitude larger than the lateral size and increases linearly with sample size up to the largest layer number L=109 the machine can handle. λM⁄L approaches a constant signifying the existence of a critical state at this particular energy. Except for the localization length for this energy, the reduced localization lengths for all other energies in both bands satisfy the single-parameter scaling law and the scaling parameter ξ is obtained and compared. The two-band lattice model with site-selective disorder has the advantage of simulating both diagonal and off-diagonal disorders over the one-band model, and the disparity between electron- and hole-doped bands can be attributed to such nonuniform disorder.View full abstractDownload PDF (427K) -
Hidekazu Mukuda, Yuhei Yamaguchi, Sunao Shimizu, Yoshio Kitaoka, Paras ...2008 Volume 77 Issue 12 Pages 124706
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe report a genuine phase diagram for a disorder-free CuO2 plane based on the precise evaluation of the local hole density (Nh) by site-selective Cu-NMR studies on five-layered high-Tc cuprates. It has been unraveled that (1) the antiferromagnetic metallic state (AFMM) is robust up to Nh≈0.17, (2) the uniformly mixed phase of superconductivity (SC) and AFMM is realized at Nh≤0.17, (3) the tetracritical point for the AFMM/(AFMM+SC)/SC/PM (paramagnetism) phases may be present at Nh≈0.15 and T≈75 K, (4) Tc is maximum close to a quantum critical point (QCP) at which the AFM order collapses, suggesting the intimate relationship between the high-Tc SC and the AFM order. The results presented here strongly suggest that the AFM interaction plays the vital role as the glue for the Cooper pairs, which will lead us to a genuine understanding of why the Tc of cuprate superconductors is so high.View full abstractDownload PDF (794K) -
Yuji Muro, Masayuki Nakano, Kiyoichiro Motoya2008 Volume 77 Issue 12 Pages 124707
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSCe2Pt3Si5 is a Kondo-lattice compound showing an antiferromagnetic transition at TN=6.3 K. We have determined the crystalline electric field (CEF) parameters by using the magnetic susceptibility and magnetization measurements of single-crystalline Ce2Pt3Si5 above TN. The obtained CEF parameters explain a Schottky-type anomaly observed in the magnetic part of specific heat. Moreover, we have measured the specific heat and magnetization under various magnetic fields applied along [010] direction to which the magnetic moments are parallel in the ordered state. Above 3 T, we observed extra anomalies in these measurements. This feature can be explained by the competition between the CEF anisotropy and the Ruderman–Kittel–Kasuya–Yosida interaction.View full abstractDownload PDF (349K) -
Annamária Kiss, Yoshio Kuramoto2008 Volume 77 Issue 12 Pages 124708
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSMechanism of successive magnetic transitions in NpFeGa5 is studied theoretically with use of an extended CEF model assuming Fe moments as the source of anisotropy. All possible dipolar and quadrupolar interactions are taken into account, which are allowed by the doublet–singlet subspace. Phase diagrams are obtained which give either two or three successive transitions from the paramagnetic phase. In the latter case, Np moments first order along [110], then tilt around the c axis, and finally tilt out of the ab-plane. The ensuing splitting pattern of 69,71Ga nuclear magnetic resonance (NMR) is analyzed theoretically, and compared with experimental results.View full abstractDownload PDF (226K) -
Takumi Takano, Taishi Takenobu, Yoshihiro Iwasa2008 Volume 77 Issue 12 Pages 124709
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSWe report the doping dependence of the transport properties of single walled carbon nanotube (SWNT) films doped with organic molecules in the low temperature. The temperature dependence of the resistance and the magnetoresistance of SWNT films are investigated systematically, and well explained by two-dimensional variable range hopping (2D-VRH) conduction scheme. We found that the magnetoresistance is dramatically reduced upon doping, and analysis based on 2D-VRH theory revealed that the sheet density of states at the Fermi level showed monotonic increase with increasing of carrier density. These results indicate that the carrier hopping in SWNT film is enhanced by the carrier doping.View full abstractDownload PDF (562K) -
Katsuyoshi Komatsu, Hideyuki Maki, Tetsuya Sato2008 Volume 77 Issue 12 Pages 124710
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSMesoscopic samples of Heisenberg spin glass (SG) with uniform sizes from 100 to 200 nm are prepared using a microfabrication method. A reduction in the peak temperature of zero-field-cooled (ZFC) magnetization in mesoscopic samples, compared with that of a film sample with the same thickness, was observed. The magnetization relaxation measurement indicates that the mesoscopic SG almost reaches the equilibrium state on a measurable time scale. The reduction in the peak temperature and the equilibration of the magnetization on an experimental time scale are interpreted as the size limitation of SG correlation length based on a droplet picture. The barrier exponents of ψ∼0.65 for a logarithmic growth law and b∼0.166 for a power growth law were estimated assuming that the droplet size is equal to the system size at the peak temperature of ZFC magnetization at ∼100 s. The field dependence of Tf, at which the ZFC and field-cooled magnetizations merge, was investigated in a mesoscopic sample and a film sample with the same thickness. The difference in Tf between both samples disappears in fields above 100 Oe, i.e., the size effect disappears. This can be explained on the basis of the field crossover length predicted in the droplet picture.View full abstractDownload PDF (330K) -
Youichi Yanase, Manfred Sigrist2008 Volume 77 Issue 12 Pages 124711
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSSuperconductivity and magnetism in the non-centrosymmetric heavy fermion compound CePt3Si and related materials are theoretically investigated. On the basis of the random phase approximation (RPA) analysis of the extended Hubbard model, we describe the helical spin fluctuation induced by the Rashba-type anti-symmetric spin–orbit coupling and identify two stable superconducting phases with either the dominant p-wave (s+P-wave) symmetry or the d-wave (p+D+f-wave) symmetry. The effect of the coexistent antiferromagnetic order is investigated in both states. The superconducting order parameter, quasiparticle density of state, NMR 1⁄T1T, specific heat, anisotropy of Hc2, and possible multiple phase transitions are discussed in detail. A comparison with experimental results indicates that the s+P-wave superconducting state is likely realized in CePt3Si.View full abstractDownload PDF (768K) -
Hideaki Sakai, Kiminori Ito, Takayuki Nishiyama, Xiuzhen Yu, Yoshio Ma ...2008 Volume 77 Issue 12 Pages 124712
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSVersatile features of impurity doping effects on perovskite manganites, R0.6Sr0.4MnO3, have been investigated by varying the doping species as well as the R-dependent one-electron bandwidth in the single-crystalline specimens. In ferromagnetic-metallic (FM) manganites (R=La, Nd, and Sm), a few percent of Fe substitution dramatically decreases the ferromagnetic transition temperature, leading to a spin glass insulating (SGI) phase for each R species. There, the correlation of charge-orbital ordering in competition with metallic ferromagnetism is effectively induced, which has been observed as an evolution of diffuse electron scattering even in the R=La system with the largest bandwidth. Such a marked impact of Fe doping, widely observed in a variety of FM manganites, virtually results in the reduction in the bandwidth for the system in the critical region near the SGI phase. We have also found a contrastive impact of Cr (or Ru) doping on a SGI manganite (R=Gd). For these dopants, the impurity-induced ferromagnetic magnetization is observed at low temperatures as a consequence of the collapse of the inherent short-range charge-orbital ordering, whereas Fe doping gives only a minimal influence. Thus, the opposite nature of Fe and Cr doping tends to generally hold for bicritical-state manganites with various bandwidths and phase correlation lengths. This may stem from the difference in magnitude of the antiferromagnetic interactions between the Fe–Fe and Cr–Cr couplings.View full abstractDownload PDF (3616K) -
Masaki Mito, Masatsugu Fujino, Yuki Komorida, Hiroyuki Deguchi, Seishi ...2008 Volume 77 Issue 12 Pages 124713
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSA thiazyl-based ferromagnet, the γ-phase of BBDTA (i.e., benzo[1,2-d:4,5-d′]bis[1,3,2]dithiazole)·GaCl4, has a high ferromagnetic ordering temperature of 7.0 K in organic radical ferromagnets. In this system, pressurization generated more compact molecular packing, resulting in that the ferromagnetic state at P=16.2 kbar is stabilized over a temperature range of more than twice of the initial range. However, the saturation magnetic moment was reduced with increasing pressure, decreasing to about 12% of the initial value even at the low pressure level of P=1.0 kbar. This suggests that the ferromagnetic molecular packing of the monoclinic γ-phase is easily transformed into that of the diamagnetic phase. Powder X-ray diffraction experiments revealed that the diamagnetic non-monoclinic (α- or β-) phase became stable instead of the monoclinic γ-phase across the pressure of 2.5–5.8 kbar. The increase in the temperature of onset of ferromagnetic state occurs in the surviving ferromagnetic domain surrounded by the diamagnetic domains.View full abstractDownload PDF (1151K) -
Osamu Sakai, Hiroyuki S. Suzuki, Hideaki Kitazawa2008 Volume 77 Issue 12 Pages 124714
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe spectral line shape of inelastic neutron excitation was theoretically studied for paramagnetic Pr ion systems with crystal-field splitting and intersite exchange interactions. It was assumed that the ground level is the doublet E (Γ3) and the excited level is the triplet T1 (Γ4) of the cubic point group. The excitation spectra are given by the superposition of two components: One has a relatively strong intensity and a sharp peak with a large dispersion; the other shows a weak and broad peak with a small dispersion. Similar features that have been observed recently in PrMg3 were explained by the calculation. The former component is ascribed to the usual E→T1 excitation with the dispersion due to the dipole-type exchange interaction, and the latter to a transition accompanied by the simultaneous excitation of fluctuation modes in the manifold at the ground level. Multipolar-type exchange interactions increase the intensity of the latter. The theory was developed based on Mori’s memory function formalism, and a symmetrized form of a standard operator was introduced to treat the multipolar interaction systematically.View full abstractDownload PDF (214K) -
Anisotropic Phase Diagram for Quadrupole Ordering and Possible Crystal Field Level Structure in TmTeRyousuke Shiina, Tatsuya Nagao2008 Volume 77 Issue 12 Pages 124715
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSThe origin of an anisotropic phase diagram for the antiferro-quadrupolar (AFQ) order in TmTe is studied using a realistic J=7⁄2 multiplet model, based on a previous analysis for the classical limit J→∞. Assuming the Γ3-type AFQ order parameters, a quantitative comparison of the phase diagram with the experiments is presented for a few candidates of the crystal field (CF) level schemes. It is shown that a scheme with a sequence from low- to high-energy levels, Γ8-Γ6-Γ7, naturally explains the observed field dependence and anisotropy of the phase diagram. The resonant x-ray scattering signals in the AFQ phase are studied to explore a possibility of identifying the order parameter and the CF scheme experimentally.View full abstractDownload PDF (219K) -
Isao Watanabe, Tadashi Adachi, Satoshi Yairi, Yoji Koike, Kanetada Nag ...2008 Volume 77 Issue 12 Pages 124716
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSZero-field and longitudinal-field muon-spin-relaxation measurements have been carried out in order to investigate the electronic and magnetic states in La2−xSrxCuO4 over a wide range of hole concentration from x=0.024 to 0.15. It has been found that the dynamic depolarization rate of muon spins in zero field starts to increase monotonically with decreasing temperature at a high temperature around 100 K. This effect is enhanced around the hole concentration of 1/8 per Cu but easily suppressed by the application of a small external field of a couple of ten gauss. The present study suggests that the dynamics of fluctuating internal fields at the muon site in the normal state of La2−xSrxCuO4 changes at a high temperature around 100 K and is correlated with the mobility of holes. Possible relationships with spin-hole stripes and the spin-gap state in the normal state are discussed.View full abstractDownload PDF (264K) -
Eri Nakamura, Shinya Yoshioka, Shuichi Kinoshita2008 Volume 77 Issue 12 Pages 124801
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSIt is well known that some kinds of animal have surprisingly brilliant colors showing beautiful iridescence. These colors are called structural colors, and are thought to originate from optical interference caused by periodic microstructures that have sizes comparable with the wavelength of light. However, much larger structural modifications can also play an important role in the coloration mechanism. In this paper, we show through careful optical and structural investigations that the structural color of the neck feather of rock dove, Columba livia, has a very comprehensive mechanism: the thin-layer optical interference phenomenon fundamentally produces the iridescence, while the layer structure is accompanied by various kinds of larger-size structural modifications that control the angular range of the reflection. Further, it is found that the granules containing melanin pigment exist in a localized manner to effectively enhance the contrast of the color caused by optical interference.View full abstractDownload PDF (826K) -
Shinya Saka, Hiroshi Takano2008 Volume 77 Issue 12 Pages 124802
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSTwo types of average structure of a single knotted ring polymer are studied by Brownian dynamics simulations. For a ring polymer with N segments, its structure is represented by a 3N-dimensional conformation vector consisting of the Cartesian coordinates of the segment positions relative to the center of mass of the ring polymer. The average structure is given by the average conformation vector, which is self-consistently defined as the average of the conformation vectors obtained from a simulation each of which is rotated to minimize its distance from the average conformation vector. From each conformation vector sampled in a simulation, 2N conformation vectors are generated by changing the numbering of the segments. Among the 2N conformation vectors, the one closest to the average conformation vector is used for one type of average structure. The other type of average structure uses all the conformation vectors generated from those sampled in a simulation. In the case of the former average structure, the knotted part of the average structure is delocalized for small N and becomes localized as N increases. In the case of the latter average structure, the average structure changes from a double loop structure for small N to a single loop structure for large N, which indicates the localization–delocalization transition of the knotted part.View full abstractDownload PDF (3872K) -
Atsushi Kamimura, Nobuyasu Ito2008 Volume 77 Issue 12 Pages 125001
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSDownload PDF (84K) -
Marc-Henri Julien2008 Volume 77 Issue 12 Pages 125002
Published: December 15, 2008
Released on J-STAGE: December 28, 2011
JOURNAL RESTRICTED ACCESSDownload PDF (80K)
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