Recursos de colección

Hokkaido University Collection of Scholarly and Academic Papers (135.711 recursos)

HUSCAP (Hokkaido University Collection of Scholarly and Academic Papers) contains peer-reviewed journal articles, proceedings, educational resources and any kind of scholarly works of Hokkaido University.

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Mostrando recursos 1 - 20 de 23

  1. Local Spin Moment Distribution in Antiferromagnetic Molecular Rings Probed by NMR

    Micotti, E.; Furukawa, Y.; Kumagai, K.; Carretta, S.; Lascialfari, A.; Borsa, F.; Timco, G. A.; Winpenny, R. E. P.
    The NMR spectra of 19F and 53Cr have been obtained at low temperatures in a heterometallic substituted antiferromagnetic (AF) ring Cr7Cd with an S=3/2 ground state and compared with the spectra in a homometallic Cr8 AF ring with an S=0 ground state. From the analysis of the spectra one can derive directly model independent values of the staggered nonuniform distribution of the local moment in the heterometallic ring Cr7Cd. The experimental values are found to be in excellent agreement with the theoretical values calculated on the basis of an effective spin Hamiltonian which includes crystal field effects.

  2. Fulde-Ferrell-Larkin-Ovchinnikov State in a Perpendicular Field of Quasi-Two-Dimensional CeCoIn5

    Kumagai, K.; Saitoh, M.; Oyaizu, T.; Furukawa, Y.; Takashima, S.; Nohara, M.; Takagi, H.; Matsuda, Y.
    A Fulde-Ferrell-Larkin-Ovchinnkov (FFLO) state was previously reported in the quasi-2D heavy fermion CeCoIn5 when a magnetic field was applied parallel to the ab plane. Here, we conduct 115In NMR studies of this material in a perpendicular field, and provide strong evidence for FFLO in this case as well. Although the topology of the phase transition lines in the H-T phase diagram is identical for both configurations, there are several remarkable differences between them. Compared to H k ab, the FFLO phase for H ⊥ ab is confined in a much narrower region at the low-T–high-H corner in the H-T plane,...

  3. Radial, sideward and elliptic flow at AGS energies

    Sahu, P.K.; Ohnishi, A.
    We study the baryon transverse in-plane (sideward) and elliptic flow from SIS to AGS energies for Au+_Au collisions in a relativistic dynamical simulation model that includes all baryon resonances up to a mass of 2 GeV as well as string degrees of freedom for the higher mass continuum. There are two factors which dominantly determine the baryon flow at these energies: the momentum dependence of the scalar and vector potentials and the resonance-string degrees of freedom. We fix the explicit momentum dependence of the nucleon-meson couplings of NL3(hard) equation of state (EoS) by the nucleon optical potential up to 1...

  4. Elliptic flow in a hadron-string cascade model at 130 GeV energy

    We present the analysis of elliptic flow at √s = 130 A GeV energy in a hadron-string cascade model. We find that the final hadronic yields are qualitatively described. The elliptic flow v2 is reasonably well-described at low transverse momentum (pT < 1 GeV/c) in mid-central collisions. On the other hand, this model does not explain v2 at high pT or in peripheral collisions and thus generally, it underestimates the elliptic flow at RHIC energy.

  5. Hadron-string cascade versus hydrodynamics in Cu+Cu collisions at √sNN = 200 GeV

    Hirano, T.; Isse, M.; Nara, Y.; Ohnishi, A.; Yoshino, K.
    Single particle spectra as well as elliptic flow in Cu+Cu collisions at √sNN =200 GeV are investigated within a hadronic cascade model and an ideal hydrodynamic model. Pseudorapidity distribution and transverse momentum spectra for charged hadrons are surprisingly comparable between these two models. However, a large deviation is predicted for the elliptic flow. The forthcoming experimental data will clarify the transport and thermalization aspects of matter produced in Cu+Cu collisions.

  6. Detection of ruptures of Andaman fault segments in the 2004 great Sumatra earthquake with coseismic ionospheric disturbances

    Heki, Kosuke; Otsuka, Yuichi; Choosakul, Nithiwatthn; Hemmakorn, Narong; Komolmis, Tharadol; Maruyama, Takashi
    [1] Near-field coseismic perturbations of ionospheric total electron content (TEC), caused by direct acoustic waves from focal regions, can be observed with Global Positioning System (GPS). They appear 10–15 min after the earthquake with typical periods of ~4–5 min and propagate as fast as ~1 km/s toward directions allowed by ambient geomagnetic fields. Ionospheric disturbance, associated with the 2004 December 26 great Sumatra-Andaman earthquake, was recorded with nine continuous GPS receiving stations in Indonesia and Thailand. Here we explore the possibility to constrain the rupture process of the earthquake with the observed ionospheric disturbances. We assumed linearly distributed point sources...

  7. Femtosecond pump–probe studies of phonons and carriers in bismuth under high pressure

    Kasami, M; Ogino, T; Mishina, T; Yamamoto, S; Nakahara, J
    We investigate the high-pressure phase of Bi under hydrostatic pressure using pump-probe spectroscopy at pressures up to 3.0 GPa, and we observe coherent phonons signal and relaxation signal of photo-excited carriers at Bi(II) and Bi(III) phases. The pressure dependence of the coherent phonons shows that the amplitude of coherent phonons is extremely small and the frequency of coherent phonons changes at high-pressure phases. As results from our experiment, we obtain its frequencies are 2.5 and 2.2 THz at Bi(II) and Bi(III), respectively. Furthermore, photo-excited carrier relaxation indicates drastic changes near 2.5 GPa. Bismuth transforms from semimetal to semiconductor near 2.5...

  8. Structural parameters determining the transition temperature of tetragonal KH2PO4-type crystals

    Ichikawa, M.; Amasaki, D.; Gustafsson, T.; Olovsson, I.
    A systematic study of the structural parameters determining the ferroelectric phase transition temperature Tc in tetragonal KH2PO4 (KDP)-type crystals MH2XO4 has been performed by searching the correlation between different structural parameters and Tc. It has been revealed that the transition temperature is determined not only by the hydrogen-bond distance R, as reported earlier, but also by the distortion of XO4 (via O-X-O angle α1) and the packing of M and XO4 along the c axis (via the rotation angle θ around the c axis); α1 reflects the dipole moment of XO4 and θ may influence the amplitude of optical vibration...

  9. Intermolecular interaction of carbon disulfide under pressure (high pressure and effective negative solvation pressure)

    Ishibashi, Y.; Mishina, T.; Nakahara, J.
    Raman spectra of liquid carbon disulfide (CS2) were measured under high pressures and in dilution with ethanol and with heptane. The pressure and concentration dependences of the molecular vibration modes 1 and 2 2 of CS2 are discussed. The intermolecular distance changes simultaneously with concentration and pressure. In addition, dilution also varies the environment around the CS2 molecule. The derivative of the intermolecular interaction energy is obtained from the frequency shift from the gas phase to the liquid phase of the 1 and 2 2 vibrations. The results show that dilution effectively acts as negative pressures, where the intermolecular distance...

  10. Coupled Oscillators in Quenched Random Potential

    Nogawa, Tomoaki; Yoshino, Hajime; Matsukawa, Hiroshi
    We study a synchronization of coupled oscillators in quenched random potential by numerical simulations as a model of sliding charge density waves and flux line lattices. By changing external driving force, we find a percolation transition of a cluster with a same frequency in a finite time observation. Percolating cluster, however, becomes unstable in the long time limit while finite size systems fall into limit cycle motion.

  11. Local Synchronization Rate in Oscillator Lattices

    Okuda, Koji; Minakuchi, Satoshi
    Oscillator lattices with random frequency distribution are numerically studied. We measured the local synchronization rate R in various oscillator lattices and found that on the lattices with more connections the oscillators are not always easier to synchronize. We also found strange behavior in which R is decreased as the coupling strength K is increased.

  12. Photoluminescence in implanted and doped silicon near room temperature

    Matsubara, Ichiro; Sasahara, Shingo; Mishina, Tomobumi; Ishibashi, Yasuhiko; Kobayashi, Toshihiko; Nakahara, Jun'ichiro
    Photoluminescence in implanted and doped silicon at room temperature is measured, and the observed structures are assigned as intrinsic phonon-assisted indirect allowed transitions. The temperature of photoexcited carriers, which is higher than the bath temperature, is estimated. For confined carriers produced by boron implantation the temperature dependence of the effective temperature of the excited carriers is the same for the different samples, but an enhancement of the photoluminescence is observed.

  13. Ultraslow dielectric relaxation process in supercooled polyhydric alcohols

    Yomogida, Yoshiki; Minoguchi, Ayumi; Nozaki, Ryusuke
    Complex permittivity was obtained on glycerol, xylitol, sorbitol and sorbitol-xylitol mixtures in the supercooled liquid state in the frequency range between 10 µ Hz and 500 MHz at temperatures near and above the glass transition temperature. For all the materials, a dielectric relaxation process was observed in addition to the well-known structural α and Johari-Goldstein β relaxation process [G. P. Johari and M. Goldstein, J. Chem. Phys. 53, 2372 (1970)]. The relaxation time for the new process is always larger than that for the α process. The relaxation time shows non-Arrhenius temperature dependence with correlation to the behavior of the...

  14. Charged vortices in high-temperature superconductors probed by NMR

    Kumagai, Ken-ichi; Nozaki, Koji; Matsuda, Yuji
    We report experimental evidence that a vortex in high-temperature superconductors (HTSC) traps a finite electric charge from the high-resolution measurements of the nuclear quadrupole frequencies. In slightly overdoped YBa2Cu3O7 the vortex is negatively charged by trapping electrons, while in underdoped YBa2Cu4O8 it is positively charged by expelling electrons. The sign of the trapped charge is opposite to the sign predicted by the conventional BCS theory. Moreover, in both materials, the deviation of the magnitude of charge from the theory is also significant. These unexpected features can be attributed to the electronic structure of the vortex in HTSC.

  15. Spin-Wave Description of Nuclear Spin-Lattice Relaxation in Mn12O12 Acetate

    Yamamoto, Shoji; Nakanishi, Takashi
    In response to recent nuclear-magnetic-resonance (NMR) measurements on the molecular cluster Mn12O12 acetate, we study the nuclear spin-lattice relaxation rate 1/T1, developing a modified spin-wave theory. Our microscopic new approach, which is distinct from previous macroscopic treatments of the cluster as a rigid spin of S=10, not only excellently interprets the observed temperature and applied-field dependences of 1/T1 for 55Mn nuclei but also strongly supports the 13C NMR evidence for spin delocalization over the entire molecule.

  16. Possible nonlinear excitations in quasi-one-dimensional halogen-bridged binuclear metal complexes

    Yamamoto, Shoji
    We investigate possible localized intragap states in quasi-one-dimensional halogen-bridged binuclear metal (MMX) complexes. Within a coupled electron-phonon model, soliton and polaron excitations in the two distinct ground states of MMX chains are numerically calculated and compared. Their effective masses are predicted for typical MMX compounds. Making a continuum-model analysis as well, we further reveal their scaling properties with particular emphasis on the analogy between MMX chains and trans-polyacetylene.

  17. Bosonic representation of one-dimensional Heisenberg ferrimagnets

    Yamamoto, Shoji
    We present a comparative study of bosonic languages to describe one-dimensional Heisenberg ferrimagnets. The ferrimagnetic Schwinger-boson mean-field theory demonstrated by Wu et al., the antiferromagnetic modified spin-wave theory designed by Takahashi, and its ferrimagnetic variant proposed by Yamamoto et al. are employed to calculate the energy structure and the thermodynamics of various ferrimagnets. A modified spin-wave scheme, which introduces a Lagrange multiplier keeping the native energy structure free from temperature and thus differs from the original Takahashi scheme, is particularly stressed as a useful tool to investigate one-dimensional quantum ferrimagnetism. The antiferromagnetic limit of these descriptions is also considered.

  18. Low-temperature thermodynamics of one-dimensional alternating-spin Heisenberg ferromagnets

    Yamamoto, Shoji; Hori, Hiromitsu
    Motivated by a novel bimetallic chain compound in which alternating magnetic centers are ferromagnetically coupled, we investigate thermodynamic properties of one-dimensional spin-(S, s) Heisenberg ferromagnets both numerically and analytically. On the one hand, quantum Monte Carlo calculations illuminate the overall thermal behavior. The specific heat may exhibit a double-peaked structure at intermediate temperatures for S3s in general. On the other hand, a modified spin-wave theory precisely describes the low-temperature properties. Expanding the specific heat and the magnetic susceptibility, we reveal an analogy and a contrast between mixed-spin ferromagnets and ferrimagnets.

  19. Entropy and spin susceptibility of s-wave type-II superconductors near Hc2

    Kita, Takafumi
    A theoretical study is performed on the entropy Ss and the spin susceptibility s near the upper critical field Hc2 for s-wave type-II superconductors with arbitrary impurity concentrations. The changes of these quantities through Hc2 may be expressed as [Ss(T,B)–Ss(T,0)]/[Sn(T)–Ss(T,0)] = 1–αS(1–B/Hc2)=(B/Hc2)αS, for example, where B is the average flux density and Sn denotes entropy in the normal state. It is found that the slopes S and at T = 0 are identical, connected directly with the zero-energy density of states, and vary from 1.72 in the dirty limit to 0.5–0.6 in the clean limit. This mean-free-path dependence of αS...

  20. Ab initio calculations of Hc2 in type-II superconductors: Basic formalism and model calculations

    Kita, Takafumi; Arai, Masao
    Detailed Fermi-surface structures are essential to describe the upper critical field Hc2 in type-II superconductors, as first noticed by and Hohenberg and Werthamer [Phys. Rev. 153, 493 (1967)] and shown explicitly by Butler for high-purity cubic Niobium [Phys. Rev. Lett. 44, 1516 (1980)]. We derive an Hc2 equation for classic type-II superconductors that is applicable to systems with anisotropic Fermi surfaces and/or energy gaps under arbitrary field directions. It can be solved efficiently by using Fermi surfaces from ab initio electronic-structure calculations. Thus, it is expected to enhance our quantitative understanding on Hc2. Based on the formalism, we calculate Hc2...

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