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Wataru Oohara, Seiji Ishiguro, Rikizo Hatakeyama, Noriyoshi Sato
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
373-376
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Dynamic structures formed due to local production of massive negative ions in a plasma are investigated by means of a one-dimensional electrostatic particle simulation which is based on a Q-machine configuration. The plasma becomes unstable with a high rate of negative ion production, being accompanied by a double-layer formation generating solitary pulses with negative potential. The solitary pulses play a role in the rapid ejection of negative ions from the system.
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Kazuki Nozawa, Nobuyuki Shima, Kenji Makoshi
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
377-380
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The structure of solid oxygen under high pressure is studied up to 6 GPa with no empirical parameters. The potential of the crystal is described by superposition of O
2 pair potentials calculated by the
ab initio method. Structural optimization is achieved with this potential energy surface. The monoclinic structure is stable up to 6 GPa and a monoclinic-orthorhombic structural transition is not found. The pressure dependence of lattice constants agrees with the result of recent X-ray diffraction experiments.
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Wei Sun, Kenji Hiraga
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
381-384
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
An Al-Ni-Ru decagonal quasicrystal with 0.4 nm periodicity, which has a good long-range basic quasiperiodic order, was observed to form in rapidly solidified Al-Ni-Ru alloys. Its structure has been studied by means of high-resolution electron microscopy and high-angle annular detector dark-field techniques, and compared with that of a superlattice Al-Ni-Ru decagonal quasicrystal formed by conventional solidification. The results reveal that the rapidly solidified Al-Ni-Ru decagonal quasicrystal with 0.4 nm periodicity has a new basic structural state which is characterized by a mixture of 2 nm atomic columnar clusters with and without pentagonal symmetry.
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Hiroshi Sawa, Emi Ninomiya, Tetsuo Ohama, Hironori Nakao, Kenji Ohwada ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
385-388
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The low-temperature (LT) superstructure of α'-NaV
2O
5 was determined by synchrotron radiation X-ray diffraction. Below the phase transition temperature associated with atomic displacement and charge ordering at 34 K, we observed Bragg peak splittings, which provide evidence that the LT structure is monoclinic. It was determined that the LT structure is (a-b)× 2b × 4c with the space group A112, where a, b and c represent the high-temperature orthorhombic unit cell. The valence estimation of V ions according to the bond valence sum method shows that the V sites are clearly separated into two groups of V
4+ and V
5+ with a zigzag charge-ordering pattern. This LT structure is consistent with resonant X-ray and NMR measurements, and is in striking contrast to the LT structure previously reported, which includes V
4.5+ sites.
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Satoshi Yotsuhashi, Kazumasa Miyake, Hiroaki Kusunose
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
389-392
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
It is shown by the Wilson numerical renormalization-group approach that a U-impurity with an f
2-singlet ground state exhibits an unstable non-Fermi liquid (NFL) fixed point due to the balance between Kondo singlet and crystalline-electric-field singlet ground state. The puzzling behavior of R
1-xU
xRu
2Si
2 (R=Th, Y and La, x≤ 0.07) can be explained if we assume that the singlet ground state is realized and the Kondo temperatures in each orbital are of different orders of magnitude. For a wide region in parameter space, the system shows the NFL behavior as a transient phenomenon in a experimentally possible temperature range. Results for the temperature dependence of resistivity, magnetic susceptibility and the Sommerfeld coefficient with and without a magnetic field reproduce the behavior observed in Th
1-xU
xRu
2Si
2. Less anomalous properties of R
1-xU
xRu
2Si
2 (R=Y and La) can be understood in the same scenario provided that these compounds have different sets of parameters.
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Yoshiro Shimojo, Makariy A. Tanatar, Takehiko Ishiguro, Reizo Kato
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2001 年 71 巻 2 号 p.
393-396
発行日: 2001年
公開日: 2003/04/25
ジャーナル
認証あり
Low-temperature magnetoresistance measurements were used to characterize the superconducting state and the electronic structure of the quasi one-dimensional salt (DMET-TSeF)
2AuI
2. The measurements revealed an essential role of small pressure created by grease molding. The small pressure suppressed the resistance jumps so that the intrinsic properties of the salt were clearly observed. The upper critical fields were determined for all three principal crystallographic directions. In contrast to strain-free samples, slightly pressurized samples show clear angle-dependent magnetoresistance oscillations related to the Fermi surface topology, demonstrating close similarity to the (TMTSF)
2X salts.
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Kazuaki Kobayashi, Kazuo Yamamoto
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
397-400
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The electronic and lattice properties of MgB
2 under a, b-axis compression are calculated. The lattice properties are optimized automatically by the first-principles molecular dynamics (FPMD) method. The features of the electronic band structures and phonon frequencies (Γ point) under uniaxial (c-axis) and a, b-axis compression are quite different from each other.
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Kazuyoshi Hirakawa
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
401-403
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
A mixture of layered compounds WS
2 and MoS
2 was found to show magnetic and electrical anomalies at low temperature. The susceptibilities showed diamagnetic properties below 9.0 K together with hysteresis upon zero-field cooling and field cooling, which suggested the existence of superconductivity in this mixture. The resistivity decreased below 9.0 K. Zero resistance was not obtained for reasons discussed.
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Takuji Nomura, Kosaku Yamada
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
404-407
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We present the highly anisotropic p-wave superconducting gap structure of Sr
2RuO
4, which was determined microscopically by solving the linearized Éliashberg equation on the basis of the perturbation theory with respect to the Coulomb energy at Ru sites. We trace the evolution of the gap function below T
c, following the elementary BCS theory, and calculate specific heat for the superconducting state with the symmetry represented by d(k) ∼ (k
x+ i k
y)ˆz. The strong momentum dependences of the gap structure provide a line-node-like power-law behavior of the specific heat even at extremely low temperature. As a result, the calculation results of specific heat agree with the experimental results well for moderately strong inter-orbit couplings.
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Jin Nakamura, Masamitsu Watanabe, Tamio Oguchi, Sin-ya Nasubida, Eiki ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
408-410
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
X-ray emission (XES) and absorption (XAS) spectra near the B-K edge were measured on single-crystalline AlB
2 compound which is an isostructural diboride of superconducting MgB
2. The partial density of states (PDOS) of B-2pσ and pπ orbitals were derived from the polarization dependence of XES and XAS spectra. There are considerable amounts of PDOS near the Fermi energy in AlB
2 similarly to that in MgB
2, but there are almost no PDOS in pσ orbitals of AlB
2 near the Fermi energy, i.e., a pseudo-gap in pσ state and a broad metallic state in pπ state are observed. The present result indirectly supports scenarios that the pσ holes play an important role in the occurrence of superconductivity in MgB
2. The overall features of PDOS were found to be in good agreement with the result of band calculation of AlB
2, but a small discrepancy in the Fermi energy is observed, which is attributed to the Al vacancy in the compounds, i.e., the estimated concentration is Al
0.93B
2.
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Takuo Sakon, Satoshi Awaji, Mitsuhiro Motokawa, David P. Belanger
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
411-413
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
High-field magnetization measurements, with H ≤ 20 T, yield the random-field Ising model (RFIM) specific heat behavior near the H-T phase boundary in Fe
0.84Zn
0.16F
2. This sample, with x greater than the magnetic vacancy percolation threshold, x
v=0.754, is in the concentration range that shows equilibrium neutron scattering line shapes at low temperature and |q|>0, unlike samples for which x<x
v. The temperature derivative of the uniform magnetization shows the expected low-field random-field Ising scaling behavior for H ≤ 18 T. At H=20 T, however, the peak temperature and amplitude are significantly suppressed, indicating a high-field RFIM region of the H-T phase diagram.
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Akira Yamaguchi, Nobuhiro Kusumi, Hidehiko Ishimoto, Hiroyuki Mitamura ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
414-417
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The magnetization of the polycrystalline manganese cluster Mn
4Br was measured down to 0.13 K under a magnetic field of ±15 kOe. It shows a gradual drop at around 1.5 K and the heat capacity measurement at 0 kOe reveals a sharp anomaly at 1.33 K, indicating the occurrence of a second-order antiferromagnetic (AFM) phase transition. The M-H curve well below the transition temperature T
N shows a step around 2.5 kOe, which probably corresponds to the transition from the AFM phase to metamagnetic (MM) phase. The observed field agrees with that estimated from T
N for the MM transition, using a simple molecular field theory. This is the first observation of a well-defined AFM and also a MM phase among the many manganese clusters with a high-spin ground state that function as molecular nanomagnets.
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Dexin Li, Yoshinobu Shiokawa, Yoshinori Haga, Etsuji Yamamoto, Yoshich ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
418-421
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The uranium intermetallic compounds U
2TSi
3 (T=Pd, Pt and Au), which crystallize in a disordered derivative of the hexagonal AlB
2-type structure, have been studied by means of ac susceptibility and electrical resistivity measurements. The experimental results and the dynamical analyses give new and important evidence for the formation of spin glass states in these systems. The origin of spin glass behavior for U
2TSi
3 is different from that for diluted metallic material or rare-earth intermetallic compounds. The competition between ferromagnetic and antiferromagnetic exchange couplings mainly mediated by the 5f-ligand hybridization in U
2TSi
3 is considered to originate from the random distribution of T and Si atoms in the crystal lattice.
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Hironori Sakai, Masaki Kato, Kazuyoshi Yoshimura, Koji Kosuge
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
422-424
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Pyrochlore oxide Tl
2Ru
2O
7, which shows a metal-insulator transition at T
MIT∼ 120 K, has been investigated using Tl-NMR measurements. The very sharp Tl-NMR spectrum in the insulating phase, whose shift is almost zero, suggests that the ground state of this compound takes a nonmagnetic spin-singlet state. The spin-lattice relaxation rate T
1-1 immediately below T
MIT suggests the presence of a spin gap between the ground and excited states. This spin-singlet state may originate from inherent geometrical frustration of pyrochlore oxide.
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Masahide Tona, Masahiro Kimura
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
425-428
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Polarization properties of single lasing microdroplets levitated in an ion trap have been investigated in both emission spectra and microscopic images. The polarization phenomena strongly depend on the observation direction and the orientation of a transparent axis of the polarization analyzer. We suggest such effects originate because excited molecular dipoles preserve the memory of the polarization of the pump field well.
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Tsuyoshi Chawanya, Kei Tokita
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
429-431
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We study the asymptotic behavior of effective degrees of freedom (i.e., the number of species or the diversity) of large-dimensional replicator equations (RE) with quenched antisymmetric random interspecies interactions. It is found that the diversity is maintained at the order of initial diversity N if the random interactions are antisymmetric, while it is known that the diversity rapidly decreases to order 1 via “extinction” in the RE with symmetric or asymmetric random quenched interactions. In the antisymmetric case, the global stability of a unique attracting set is contrasted to the symmetric and asymmetric cases which have many attractors in general. The present result suggests a new mechanism of maintaining biodiversity which resolves the “paradox of ecology”.
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Tsuyoshi Hondou
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
432-436
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
A dramatic development occurring in our daily life is the increasing use of mobile equipment including mobile phones and wireless access to the Internet. They enable us to access several types of information more easily than in the past. Simultaneously, the density of mobile users is rapidly increasing. When hundreds of mobile phones emit radiation, their total power is found to be comparable to that of a microwave oven or a satellite broadcasting station. Thus, the question arises: what is the public exposure level in an area with many sources of electromagnetic wave emission? We show that this level can reach the reference level for general public exposure (ICNIRP Guideline) in daily life. This is caused by the fundamental properties of electromagnetic field, namely, reflection and additivity. The level of exposure is found to be much higher than that estimated by the conventional framework of analysis that assumes that the level rapidly decreases with the inverse square distance between the source and the affected person. A simple formula for the exposure level is derived by applying energetics to the electromagnetic field. The formula reveals a potential risk of intensive exposure.
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Zhen-ya Yan, Hong-qing Zhang
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
437-442
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
In this paper, the generalization of integrable (2+1)-dimensional dispersive long-wave equations (GIDLWE) introduced by Boiti
et al. is investigated. The idea of the homogeneous balance method, which is very concise and primary, is extended and applied to GIDLWE. As a result, multiple soliton-like solutions, which contain the single soliton-like solutions, double soliton-like solutions and periodic-like solutions are constructed for the GIDLWE. In addition, by using a transformations we find that the GIDLWE can be reduced to be the Burgers equation with the external force which can be used to search for more exact solutions of GIDLWE. This approach is also extended to other nonlinear evolution equations in mathematical physics.
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B. Grammaticos, T. Tamizhmani, A. Ramani, A. S. Carstea, K. M. Tamizhm ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
443-447
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We present the list of all known to date difference and q-discrete forms of the Painlevé I equations. A new, derived here for the first time, zero-parameter, q-discrete Painlevé equation is also given. We present interrelations between some of these equations, whenever they exist, in the form of Miura transformations. Finally we give the bilinearisation of these systems.
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B. Z. Essimbi, I. V. Barashenkov
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
448-452
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Nonlinear localized excitations in a bi-inductance electrical line are considered analytically by means of the method of multiple scales combined with a quasi-discreteness approximation. We show in a unified way that the system may support new types of gap solitons (with the frequency of oscillations lying in the gap of the continuous wave spectrum) and intrinsic localized modes (with the oscillation frequency being above all the phonon bands). Both kinds of excitations have zero group velocity.
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Hang-yu Ruan
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
453-457
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
A variable separation approach is used to obtain exact solutions of high dimensional nonlinear physical models. Taking the breaking soliton equation as a simplify example, we show that a high dimensional nonlinear physical model may have quite rich localized coherent structures. For the breaking soliton equation, the richness of the localized structures caused by the entrance of some variables separated arbitrary functions. Some special types of the dromion solutions, lumps, ring solitons, curved solitons and breathers solution etc. are discussed by selecting the arbitrary functions appropriately.
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Katsuki Katayama, Tsuyoshi Horiguchi
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
458-465
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We investigate an on-line learning of two-layered feed-forward neural networks with randomly diluted connections by using a gradient descent algorithm. We derive coupled first-order differential equations for order parameters which describe learning process in the thermodynamic limit by assuming the self-averaging within the framework of the statistical physics. We clarify that the learning time for asymmetric dilution of connections in a teacher network is shorter than the learning time for symmetric dilution of the connections in the teacher network. But we find that the learning does not converge when the teacher network is too diluted. We obtain a phase diagram in a learning rate versus rate of dilution plane for the diluted teacher network. It turns out that the learning converges imperfectly when a student network is diluted too much, because the average value of connections for the student network is essentially smaller than the value of connection for the teacher network.
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Shinichi Sato
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
466-469
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
For two-dimensional Eden growth and ballistic deposition, the most probable growth path for a given cluster is studied by making use of the ensemble average taken over all possible growth paths. A dynamical system associated with the most probable growth is introduced and its orbits are observed numerically. The numerical results suggest that the dynamical system can be modeled by a map with finite degrees of freedom.
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Fumihiko Aiga, Tsukasa Tada
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
470-475
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
A new formulation of the optimized effective potential (OEP) method is presented. Our OEP method is applicable to the linear combination of atomic orbital (LCAO) calculation for systems which have degenerate orbitals, in contrast to the conventional OEP method. An approximation to our OEP equation for the exchange-correlation (xc) potential, similar to the KLI approximation, is derived.
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Eiichirou Kawamori, Teruo Tamano, Yousuke Nakashima, Masayuki Yoshikaw ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
476-482
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We revealed experimental observation indicating density limit with gas-puff fueling in hot ion mode plasmas of the GAMMA 10 tandem mirror. The responses of the plasmas for the various gas fueling were studied. Despite the increase in the quantity of the particle source, the line average density was saturated with the degradation of the radial particle confinement at the periphery of the central plasma. It was clarified that the line density obtained with the pellet fueling is about 20-50% higher than that with gas-puffing in the same average ion temperature. The clear difference between the pellet fueling and the gas fueling was observed in the radial profile of particle deposition at the central midplane. From the consideration based on the experimental observation, a radial-loss mechanism of ions by charge exchange reaction was discussed as an explanation for the degradation of particle confinement at the plasma periphery.
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Kenjiro Kanamitsu, Susumu Saito
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
483-486
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Using the density-functional electronic-structure calculations, we study so-called zig-zag carbon nanotubes. From the complete geometry optimization, it is found that two kinds of bond lengths are considerably different from each other. They possess strong tube-diameter dependence. We determine the bond lengths up to the order of 10
-2 Å and the bond angles to 10
-2degree. In addition, changes of the electronic band structure upon the geometry relaxation from the uniform bond-length tube are found to be sizable. Also the electronic properties and energetics obtained for optimized geometries are discussed.
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Dong-Seok Yang, Ikgyun Kim, Yong-Goo Yoo, Seong-Cho Yu
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
487-490
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Co
50C
50 alloys were fabricated by mechanical alloying process from the mixed powder of pure cobalt and carbon. The variations of the local structure and magnetic properties were examined by EXAFS analysis and the VSM magnetometer. It is shown that the alloying was progressed as the milling time increases. The significant changes of the magnetization and the structure has been occured in 12 h milling. EXAFS spectrum and its Fourier transform confirms that the final product is in the amorphous state. The EXAFS spectrum of the alloy milled for 24 h was fitted to the conventional EXAFS equation. The interatomic distances obtained from the fitting were 1.94 ± 0.02 Å for Co-C pair and 2.52 ± 0.02 Å for Co-Co pair, respectively. The magnetization was almost saturated in 24 h milling.
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Yuzuru Miyazaki, Mitsuko Onoda, Takeo Oku, Masae Kikuchi, Yoshinobu Is ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
491-497
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We have determined the crystal structure of the composite crystal [Ca
2CoO
3]
0.62CoO
2, known as Ca
3Co
4O
9, by a superspace group approach. Structural parameters were refined with a superspace group of Cm (0 1-p 0) using powder X-ray and neutron diffraction data. The compound consists of two interpenetrating subsystems of a CoO
2 sheet and a distorted triple-layered NaCl-type Ca
2CoO
3 block, being incommensurate parallel to the b-axis. The CoO
2 sheet is composed of a CdI
2-type triangular Co lattice with sharing an edge of the CoO
6 octahedra. In the Ca
2CoO
3 subsystem, “<”-shaped buckled arrangement of the atoms is found, due to the ordered arrangement of the Ca and Co atoms parallel to the c-axis. Both the subsystems have common a-, c-axes and β-angle with a=4.8339(3) Å, c=10.8436(7) Å and β=98.14(1)
º. The b-axis lengths are refined to be b
1=2.8238(2) Å for the [CoO
2] subsystem and b
2=4.5582(2) Å for the [Ca
2CoO
3] subsystem. An undulating arrangement of the O atom sites in the CoO
2 sheets is revealed but the modulation of the Co atom site is less marked. Remarkable displacive modulation of the Co and O sites in the [Ca
2CoO
3] subsystem has also been observed, suggesting that a regular NaCl-type coordination is very severe for the Co-O bonds in the present compound.
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Fumihito Shikanai, Masaru Komukae, Zbigniew Czapla, Toshio Osaka
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
498-503
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
X-ray investigation was carried out to examine the ferroelectric phase transition in glycinium phosphite, NH
3CH
2COOHH
2PO
3, from the structural point of view. The result indicates that the crystal belongs to the space group P2
1 in the ferroelectric phase and the unit cell parameters obtained at 198 K are a=9.758(2) Å, b=8.510(1) Å, c=7.375(1) Å and β=100.47(1)
º. The crystal structure in ferroelectric phase was determined using an automatic four-circle diffractometer and refined to R=0.032 and R
w=0.023 for 2685 independent reflections. Structure analysis clarified that in the ferroelectric phase, the hydrogen atoms between neighboring phosphite tetrahedra are in the ordered state and phosphite tetrahedra deform from those in the paraelectric phase.
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Ayano Chiba, Yoshinori Ohmasa, Makoto Yao, Oleg Petrenko, Yukinobu Kaw ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
504-508
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We have carried out neutron scattering experiments for liquid Te
50Se
50 at 700 K (semiconducting regime), 900 K (transition regime) and 1100 K (metallic regime). The quasielastic scattering peak is comparatively narrow at the peak positions of S(Q). A remarkable increase in the peak width is observed near the first minimum of S(Q), when the semiconductor-to-metal transition occurs. Since the first peak of S(Q) in this system proves to mainly reflect the inter-chain correlation and the second peak to the intra-chain correlation, the observed broadening may suggest frequent bond-switching between the chains in the metallic regime.
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Hiroyuki Uehara, Jun Hatano
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
509-512
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The pressure-temperature phase diagrams of the ferroelectric liquid crystals FLC-031 and FLC-032 were obtained from the complex dielectric constant. As the pressure increases, all the transition temperatures increase. On heating, the temperature width of the smectic phase is almost independent of the pressure, while the width of the ferroelectric chiral smectic C (SmC
*) phases reduces with pressure and disappears at 300 MPa and 125
ºC for FLC-031 and 160 MPa and 102
ºC for FLC-032. On the other hand, the width of the paraelectric smectic A (SmA) phase increases with increasing pressure. Therefore, this indicates that, for FLC-031 and FLC-032, the application of pressure reduces the stability of the SmC
* phase, while the stability of the SmA phase increases. Moreover, there is no systematic relation between the length of the non-chiral alkyl chain in molecules and the decreasing rate of the width of the SmC
* phase with pressure.
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Yoshinori Shibata, Yukinori Ohta
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
513-518
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We consider the possible charge and orbital ordering in a Hollandite compound Bi
xV
8O
16, which is a new one-dimensional triangular-lattice t
2g-orbital system. Using the strong-coupling perturbation theory, we derive the effective spin-orbit Hamiltonian in the approximation neglecting the small off-diagonal hopping parameters or orbital fluctuation, whereby we obtain the spin Hamiltonians in the partial space of each orbital-ordering pattern. We then apply an exact-diagonalization technique on small clusters to these spin Hamiltonians and calculate the ground-state phase diagram. We find that a variety of orbital-ordering patterns appear in the parameter space, which include the state characterized by the partial spin-singlet formation consistent with recent NMR experiment.
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Tatsuki Oda
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
519-524
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We have implemented a new Car-Parrinello dynamics for metallic systems. In this scheme, including fractional occupations of Kohn-Sham orbitals, the dynamical variables representing electronic wave functions are extended to two kinds of freedom, the conventional fictitious variables and the variables related with the unitary transformation among the orbitals. The applications to liquid Si and Al yielded the satisfactory results, compared with the previous works. The trajectory of electronic freedoms was shown to always evolve just above the Born-Oppenheimer surfaces.
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Tadahiko Chida, Shugo Suzuki, Kenji Nakao
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
525-537
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We study the spectral densities for alkali-metal-doped C
60, A
xC
60 (A=K, Rb, etc), at zero temperature to elucidate the origin of anomalous behaviors in photoemission spectra, based on the dynamical mean-field theory by using the exact diagonalization method. The results for A
2C
60 and A
4C
60 agree qualitatively with the results of Hartree-Fock calculations; these materials are insulating due to the cooperation between the electron-electron and electron-phonon interactions. On the contrary, in A
3C
60, the competition between the electron-electron and electron-phonon interactions results in the charge fluctuation and consequently the material remains metallic. We find satellites at about 1.6 eV below and above the Fermi level and the enhancement of the spectral intensity at the Fermi level in the spectral density for A
3C
60. These originate from the charge fluctuation. Furthermore, it is found that continuous features ranging from -1 eV to +1 eV are derived from the multiplet splitting of C
602- and C
604- molecules. Our results for A
3C
60 successfully explain the anomalous behaviors in the photoemission spectra of A
3C
60. Moreover, we study the photoemission spectra of a C
603- molecule in a particle bath at finite temperature. The result is in qualitative agreement with the observed temperature dependence of the photoemission spectra of A
3C
60.
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Makoto Ambai, Yoshiaki Kobayashi, Satoshi Iikubo, Masatoshi Sato
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
538-542
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Transport and Cu-NQR studies have been carried out for the T
*-type high temperature superconducting Cu oxide Nd
1.6-xCe
xSr
0.4CuO
4 with single layered CuO
2 planes formed by CuO
5 pyramids. No anomaly related to the static or quasi static “stripe” order has been observed in the temperature T and x dependence of the thermoelectric powers S. We have not found such kind of anomaly in the x dependence of the superconducting transition temperature T
c, either. Although the decrease of the Cu NQR intensity with decreasing T (wipeout) has been observed in this system, it can be understood by considering the loss of the itinerant nature of the electrons, which takes place in the proximity region of the metal-insulator phase boundary, and cannot be connected with the static or quasi static “stripe” order.
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Masahiro Hara, Akira Endo, Shingo Katsumoto, Yasuhiro Iye
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
543-549
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We have studied the transport in two-dimensional electron gas (2DEG) subjected to two different types of magnetic barriers-dipolar and monopolar barriers-using fringing magnetic field from ferromagnetic film on the surface of GaAs/AlGaAs heterostructures. Resistivity of 2DEG increases as the magnetic barriers are turned on. We measured amplitude dependence and temperature dependence of the excess resistivities due to those magnetic barriers. The resistance as a function of the uniform component of the magnetic field exhibits a positive magnetoresistance and a beating pattern of the Shubnikov-de Haas oscillations. They are qualitatively explained by considering the various cyclotron trajectories in the region of the magnetic barriers.
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Yositake Takane
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
550-568
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
The dc Josephson effect in a one-dimensional Tomonaga-Luttinger (TL) liquid is studied on the basis of two bosonized models. We first consider a TL liquid sandwiched between two superconductors with a strong barrier at each interface. Both the interfaces are assumed to be perfect if the barrier potential is absent. We next consider a TL liquid with open boundaries, weakly coupled with two superconductors. Without putting strong barriers, we instead assume that the coupling at each interface is described by a tunnel junction. We calculate the Josephson current in each model, and find that the two models yield same results. The Josephson current is suppressed by repulsive electron-electron interactions. It is shown that the suppression is characterized by only the correlation exponent for the charge degrees of freedom. This result is inconsistent with a previously reported result, where the spin degrees of freedom also affects the suppression. The reason of this inconsistency is discussed.
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Kazuhiko Hasegawa, Wilson Agerico Diño, Hideaki Kasai, Ayao Oki ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
569-573
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
A model is presented to describe the dynamics of an acetylene on Cu(100) induced by STM, where the relation between the change of the corresponding electron system caused by an electron tunneling from an STM tip to the metal substrate via the adsorbed acetylene, and the transition of the vibrational state for the intramolecular motion is taken into account. With this model, we can reproduce the experimentally measured dissociation probability of C
2H
2(C
2D
2) into C
2H(C
2D) and H(D) when the STM tip is set at a position above the center of the C-C bond of an adsorbed C
2H
2(C
2D
2).
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Akinori Irizawa, Tomohiko Ohmura, Tomohiko Shibata, Masaki Kato, Kazuy ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
574-581
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Magnetic susceptibility and electric resistivity were measured on Y
2Ba
4Cu
7O
15-δ over the whole oxygen deficiency range, 0≤δ≤1. Complete collapse of superconductivity was observed for Y
2Ba
4Cu
7O
14 in both resistivity and susceptibility measurements, although there still reside the metallic conduction. This is the first observation of under-doped
normal metallic state in high-T
c cuprates without applying any external factors such as magnetic field, hydrostatic pressure or substitution of impurity for plane-Cu site for breaking the superconducting state. The behavior of electric conduction due to the CuO
2 plane was observed in resistivity measurement as changing from the
T-linear dependence to the under-doped
S-shaped temperature dependence, giving the spin-gap temperature which agree well with the results from the spin-lattice relaxation rate 1/T
1 for Cu NQR at plane-site in various YBCO compounds. The temperature dependence of 1/T
1 on plane-site Cu in Y
2Ba
4Cu
7O
14 is discussed to be of itinerant-electron type with finite magnetic correlation between them as in the case of nearly and/or weak magnetic systems. The temperature dependence of 1/T
1 on chain-site is also discussed among various YBCO compounds.
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M. El Massalami, R. E. Rapp, E. F. Chagas, H. Takeya, J. Flores, C. M. ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
582-586
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Using magnetic specific heat [C
M(T)], we investigated the character and dimensionality of the spin wave excitations within the coexistence phase of single crystal ErNi
2B
2C. As known, the magnetic structure of ErNi
2B
2C consists of a transversely polarized sinusoidally modulated state that is squared-up, presumably, below the onset point of the weak ferromagnetic state T
WF ≈ 2.2 K. We observed that the thermal evolution of C
M(T) within the sinusoidally modulated state (T
WF<T<T
N) is distinctly different from the one below T
WF: for T
WF<T<T
N, C
M(T) evolves as 0.45 T
2 J/mol K suggesting a 2d excitations with a gapless linear dispersion relation. On the other hand, for T< T
WF, C
M(T) is dominated by an exponential factor, indicative of gapped AF excitations. The gap (∼6 K) is approximately equal to T
N and to the separation between the lowest lying Kramer doublets. Finally, based on entropy arguments and on features of the exchange striction, we comment on the influence of the magnetoelastic coupling on the low-temperature magnetic properties of this compound.
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Ryusuke Ikeda
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
587-593
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Motivated by recent resistance data in high T
c superconductors under magnetic fields parallel to the CuO layers, we address two key issues on the Josephson-vortex phase diagram, an appearance of structural transitions on the observed first order transition (FOT) curve in intermediate fields and of a lower critical point of the FOT line. The structural transitions reflected on the thermal transition curve in YBCO are identified based on our mean field calculation, and it is argued that a lower critical point more easily occurs in the present B ⊥ c case compared with that in B || c case.
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Takayuki Asano, Hiroyuki Nojiri, Wataru Higemoto, Akihiro Koda, Ryosuk ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
594-598
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Zero-, longitudinal- and transverse-field μSR experiments are performed for a linear chain antiferromagnet Cu benzoate, Cu(C
6H
5COO)·3H
2O, and no long range order (LRO) is found down to 20 mK. The upper limit of the ratio of the Néel temperature to the exchange coupling, k
BT
N/J<0.002, is even better than that of Sr
2CuO
3, which is known as the best candidate of S=1/2 antiferromagnetic Heisenberg quantum spin chain. Significance of our findings is discussed in view of whether there is a non-zero critical coupling ratio necessary for LRO in coupled Heisenberg chains.
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Yukio Yasui, Masaki Kanada, Masafumi Ito, Hiroshi Harashina, Masatoshi ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
599-606
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Static and dynamical properties of the magnetic moment system of pyrochlore compound Tb
2Ti
2O
7 with strong magnetic frustration, have been investigated down to the temperature T=0.4 K by neutron scattering on a single crystal sample. The scattering vector (Q)-dependence of the magnetic scattering intensity becomes appreciable with decreasing T at around 30 K, indicating the development of the magnetic correlation. From the observed energy profiles, the elastic, quasi elastic and inelastic components have been separately obtained. The quasi elastic component corresponds to the diffusive motion of the magnetic moments within the lowest states, which are formed of the lowest energy levels of Tb
3+ ions. Magnetic correlation pattern which can roughly reproduce the Q-dependence of the scattering intensities of the elastic and quasi elastic component is discussed based on the trial calculations for clusters of 7 moments belonging to two corner-sharing tetrahedra. A possible origin of the glassy state, which develops at around 1.5 K with decreasing T is discussed.
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Yoshiki Yonamoto, Toshihiko Yokoyama, Kenta Amemiya, Daiju Matsumura, ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
607-612
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
N K-, O K- and Co L
III,II-edge X-ray magnetic circular dichroism (XMCD) was investigated for NO adsorbed on ultrathin
fcc-Co(001) films which show both in-planar and perpendicular magnetic anisotropies. Large suppression of spin and orbital magnetic moments of Co was observed upon NO adsorption. Both N and O K-edge XMCD spectra show negative signs at the NO 2π
* resonance, irrespective of in-plane and perpendicular magnetic anisotropies. This finding implies the parallel alignment of the NO 2π
* orbital magnetic moments with the total magnetization. The results are comparatively discussed with the previous works on CO on Co and Ni films and are interpreted by a simple chemical bonding scheme.
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Yoichi Okimoto, Yoshinori Konishi, Makoto Izumi, Takashi Manako, Masas ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
613-617
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Optical conductivity spectra (σ(ω)) were investigated for coherently strained epitaxial films of tetragonal La
1/2Sr
1/2MnO
3 with various c/a ratios (1.04, 1.00, and 0.98). With decreasing c/a, σ(ω) in the ground state shows a successive dramatic change from an insulating gap-like to metallic but highly incoherent spectrum, then to a pseudo-gap one, which reflects the strain-induced e
g orbital ordering/disordering and the resultant different spin structures. The variation of the electronic structure induced by such a strain-orbital coupling is discussed in comparison with some theoretical models.
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Tatsuya Nagao, Jun-ichi Igarashi
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
618-624
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
We theoretically investigate the Raman scattering in the quadrupolar ordering phase of CeB
6, on the basis of the model Hamiltonian of Shiba
et al. Approximating the total susceptibility by a sum of quadrupole moments of each Ce atom, we calculate the Raman spectra corresponding to the orbital excitations in the Γ
8 states within the random phase approximation. We obtain the spectra consisting of several peaks as a function of frequency shift. They are found to depend strongly on the polarization of light. We discuss also the temperature and the magnetic field dependences of the spectra.
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Hitoshi Takemura, Chisato Ogihara, Kazuo Morigaki
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
625-629
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Lifetime resolved measurements of photoluminescence (PL) have been done under pulsed excitation for a-Si:H based films including those having nanometer sized structure. The results of the lifetime resolved PL are understood by considering two components. We observed a component of lifetimes longer than 1 μs which is considered to be due to localized electron-hole pairs. Another component was observed around 10 ns in the lifetime distributions. In the case of a-Si:H the PL is dominated by the longer lifetime component and the 10 ns component is observed only for high energy PL. On the other hand, the 10 ns component is dominant and stable against raising temperature in the case of the films in which the confinement effect of electrons and holes is significant. In the case of a-Si
1-xN
x:H alloy films, the 10 ns component is also dominant and stable against raising temperature. These results suggest that the 10 ns component is due to singlet excitons being stable by confinement effect or decreasing dielectric constant. These results are also consistent with triplet exciton model which was used to explain the results of lifetime resolved PL in millisecond region in a-Si:H based films in our previous paper.
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Ikuko Akimoto, Ken-ich Kan'no
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
630-643
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Photoluminescence and near-band-edge electronic structure of pristine C
60 single crystals have been investigated in the low temperature phase below 90 K. By applying two-photon excitation spectroscopy, a monomorphic spectrum is extracted from the several crystals which exhibit apparent diversity for ordinary one-photon excitation. Also, a localized absorption band with discrete vibronic sub-peaks is clearly confirmed at 1.685 eV below the fundamental absorption edge (1.815 eV). Overall features of the luminescence-line-narrowing spectrum obtained by site-selective excitation into the localized absorption band are assigned to the vibronic progressions coupled with the Raman-active gerade-symmetry modes of individual C
60 molecules (i.e., eight h
g, two a
g, and their combinations), accompanied by phonon-sidebands due to cooperative librations and intermolecular translations. The origin of photoluminescence and its relaxation kinetics are fully discussed in connection with the inhomogeneously broadened localized states which are presumably due to perturbed Frenkel excitons stabilized with symmetry-lowering by adjacent intrinsic defect or some lattice disorder.
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Shin-ichiro Kondo, Seiichiro Nakabayashi, Antonis Karantonis
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
644-649
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
A prediction method is proposed for one-step and multi-step forecasting of the chaotic response. The method is based on the determination of the transition matrix from experimental data by a linearization procedure. The procedure is applied to various chaotic time series obtained from the electrochemical oscillator Fe/H
2SO
4. The one-step prediction results are good in the case of smooth time series. Regions of poor prediction are analyzed and it is found that the forecasting is limited due to the presence of a high frequency component in the time series causing a virtual increase of the measuring interval, Δ t. The method is also applied successfully for multi-step prediction. The performance is increased by implementing a false neighbors detection routine.
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Kazuhiko Watanabe, Jun-ichi Wakita, Hiroto Itoh, Hirotoshi Shimada, Sa ...
原稿種別: General Physics
専門分野: Mathematical methods in physics.
2002 年 71 巻 2 号 p.
650-656
発行日: 2002年
公開日: 2003/04/25
ジャーナル
認証あり
Spatio-temporal patterns emerged inside a colony of bacterial species
Proteus mirabilis on the surface of nutrient-rich semisolid agar medium have been investigated. We observed various patterns composed of the following basic types: propagating stripe, propagating stripe with fixed dislocation, expanding and shrinking target, and rotating spiral. The remarkable point is that the pattern changes immediately when we alter the position for observation, but it returns to the original if we restore the observing position within a few minutes. We further investigated mesoscopic and microscopic properties of the spatio-temporal patterns. It turned out that whenever the spatio-temporal patterns are observed in a colony, the areas are composed of two superimposed monolayers of elongated bacterial cells. In each area they are aligned almost parallel with each other like a two-dimensional nematic liquid crystal, and move collectively and independently of another layer. It has been found that the observed spatio-temporal patterns are explained as the moiré effect.
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