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Tomotsugu Wakasa, Hideyuki Sakai, Hiroyuki Okamura, Hideaki Otsu, Taka ...
2004 Volume 73 Issue 7 Pages
1611-1614
Published: July 15, 2004
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A complete set of polarization transfer observables has been measured for the
90Zr(
p,
n) reaction at
Tp=295 MeV and θ
lab=0°. The measurement can yield the total spin transfer Σ(0°) which is independent of nuclear reaction mechanisms such as the effective nucleon–nucleon interaction or distortions. The deduced Σ(0°) values indicate the strong spin-flip characteristics of the continuum up to 50 MeV excitation. A predominance of unnatural-parity transitions in the continuum is also observed from polarization transfer observables.
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Takashi Kamiyama, Shinya Hosokawa, Alfred Q. R. Baron, Satoshi Tsutsui ...
2004 Volume 73 Issue 7 Pages
1615-1618
Published: July 15, 2004
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The dynamic scattering factor
S(
Q,ω) was measured by high-resolution inelastic X-ray scattering using intense X-rays from a third-generation synchrotron radiation facility. The observed spectra demonstrate the existence of longitudinal propagating modes at small
Q values, although the collective excitations are highly damped (not overdamped) as in the classical van der Waals liquid Ar. The
Q–ω relation of the excitation shows a positive dispersion of about 37%, much larger than in liquid metals but similar to that in liquid Ar. The collective dynamics of liquid CCl
4 at small
Q values can be interpreted in the framework of classical dense liquids.
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Shun-ichi Yoshida, Koji Nemoto, Koh Wada
2004 Volume 73 Issue 7 Pages
1619-1622
Published: July 15, 2004
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We found that the true ground state of a dipolar spin ice system under a [110] magnetic field is a “
Q=
X” structure, which is consistent with both experiments and Monte Carlo simulations. We performed a Monte Carlo simulation to confirm the existence of a first-order phase transition under a [110] magnetic field. The result indicates the existence of the first-order phase transition to the “
Q=
X” phase in a magnetic field above 0.35 T for Dy
2Ti
2O
7. In this letter we show a magnetic field-temperature phase diagram to summarize the ordered states of this system.
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Yoshihiro Shimomura, Shin Miyahara, Nobuo Furukawa
2004 Volume 73 Issue 7 Pages
1623-1626
Published: July 15, 2004
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We investigated the double-exchange spin ice (DESI) model on a kagomé lattice by Monte Carlo simulation to study the effects of a geometrical frustration, and the mechanism that generates an ordered state in a metallic system. The DESI model on the kagomé lattice is a frustrated metallic system due to an effective ferromagnetic interaction between localized spins caused by the double-exchange (DE) mechanism and a uniaxial anisotropy for the localized spins. A dodecagonal spin cluster (named dodecamer), which consists of twelve localized spins, appears at low temperature when the number of particles per site
n\\simeq1⁄3–1⁄2. Such a dodecamer order is driven by both the kinetic energy gain due to the DE mechanism and the geometrical frustration. We discuss that cluster orders, in general, may be a common feature in itinerant electron systems coupled with frustrated adiabatic fields.
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Nobuhiro Shiotani, Isao Matsumoto, Hiroshi Kawata, Jinya Katsuyama, Ma ...
2004 Volume 73 Issue 7 Pages
1627-1630
Published: July 15, 2004
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Direct experimental information about the geometry of the Fermi surface of Ti
48.5Ni
51.5 whose martensitic transformation temperature is 170 K is presented for the first time. The present results have shown four sheets of the Fermi surface with the same topology, but with different shapes and sizes, as those predicted previously by band structure computations. From geometrical features of the Fermi surface, new possible nesting features of the electron surface at R and the hole surface at Γ are suggested for future theoretical computations of the generalized susceptibility and phonon spectra of this alloy system.
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Koichi Hamada, Daijiro Yoshioka
2004 Volume 73 Issue 7 Pages
1631-1634
Published: July 15, 2004
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The doping and temperature dependences of the Fermi arc in the staggered-flux, or the
d-density wave, ordered phase of the
t–
J model are analyzed using the U(1) slave boson theory. Nontrivial behavior is revealed by the self-consistent calculation. In the low doping and finite-temperature region, both the length of the Fermi arc and the width of the Fermi pocket are proportional to δ and the area of the Fermi pocket is proportional to δ
2. This behavior is completely different from that at zero temperature, where the area of the Fermi pocket becomes π
2δ. This behavior should be observed by detailed experiments of angle-resolved photoemission spectroscopy in the pseudogap phase of high-
Tc cuprates if the pseudogap phase is the staggered-flux ordered phase.
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Tadahiko Ishikawa, Masaaki Kurita, Hiroaki Shimoda, Yohei Sakano, Shin ...
2004 Volume 73 Issue 7 Pages
1635-1638
Published: July 15, 2004
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Photoconductivity and various photo-magnetotransport properties have been studied in quantum paraelectric SrTiO
3 crystals. SrTi
16O
3 shows giant photoconductivity, as reported before. The photodoped carrier in the
16O system is of electron type and has high mobility beyond 10
4 cm
2 V
−1 s
−1 at 5 K. Its number can reach the order of 10
15 cm
−3. In contrast, isotope-substituted SrTi
18O
3 is not a good photoconductor. In addition, the photocarrier’s mobility in the
18O sample is negligibly small. These results suggest a strong correlation between the quantum fluctuation and the giant photoconductivity in this quantum paraelectric system. In other words, the study of photocarrier dynamics is a novel approach to the investigation of quantum fluctuation in dielectric materials.
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Daijiro Yoshioka
2004 Volume 73 Issue 7 Pages
1639-1642
Published: July 15, 2004
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A shot noise at filling factor ν=2⁄5 is investigated theoretically. It is argued that the “charge”
e* measured by the noise at absolute zero is not the quasiparticle charge but simply the filling factor times the electron charge
e, namely
e*=2
e⁄5. At a higher temperature, quasiparticles with charge
e*=±
e⁄5 begin to contribute to backscattering, and the shot noise provides charge
e*=
e⁄5. This theory explains the recent experiment by Chung
et al. [Phys. Rev. Lett.
91 (2003) 216804].
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Mitake Miyazaki, Takashi Yanagisawa, Kunihiko Yamaji
2004 Volume 73 Issue 7 Pages
1643-1646
Published: July 15, 2004
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We studied the ground state of the two-dimensional Hubbard model near half filling on the square lattice. Using Variational Monte Carlo method, we show that the diagonal stripe state of bond-centered type, in which the domain wall is located between two sites, becomes more stable than the vertical stripe state when the doping hole density
x is as low as
x\\simeq0.06. The inverse of stripe periodicity δ and the hole density
x are observed to have the relationship δ∼
x (δ<
x) for the bond-centered diagonal stripe state (the vertical stripe state) in the light-doping region. These results are in good agreement with elastic neutron scattering experiments in La
2−xSr
xCuO
4.
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S. Kawasaki, T. Mito, Y. Kawasaki, H. Kotegawa, G.-Q. Zheng, Y. Kitaok ...
2004 Volume 73 Issue 7 Pages
1647-1650
Published: July 15, 2004
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We report the discovery of new superconducting and novel magnetic phases in CeIn
3 on the verge of antiferromagnetism (AFM) under pressure (
P) through the In-nuclear quadrupole resonance (NQR) measurements. We have found a
P-induced phase separation of AFM and paramagnetism (PM) without any trace of a quantum phase transition in CeIn
3. A new type of superconductivity (SC) was found, under
P=2.28–2.5 GPa, to coexist with AFM. It is magnetically separated from PM where the heavy fermion SC takes place. We propose that the magnetic excitations such as spin-density fluctuations induced by the first-order magnetic phase transition might mediate attractive interaction to form Cooper pairs.
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Zenji Hiroi, Shigeki Yonezawa, Yuji Muraoka
2004 Volume 73 Issue 7 Pages
1651-1654
Published: July 15, 2004
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Superconductivity in the potassium osmium oxide KOs
2O
6 crystallizing in the β-pyrochlore structure is studied by electrical resistivity, magnetic susceptibility and specific heat measurements. It is the second superconductor in the family of pyrochlore oxides, following the α-type pyrochlore oxide Cd
2Re
2O
7 which is believed to be a conventional
s-wave superconductor. The superconducting transition temperature
Tc of KOs
2O
6 is 9.6 K, almost one order higher than the
Tc=1.0 K of Cd
2Re
2O
7. Moreover, the superconductivity of KOs
2O
6 is markedly robust under high magnetic fields, with a large upper critical magnetic field
Hc2 of about 38 T, which seems to exceed Pauli’s limit expected for conventional superconductivity. This is also in contrast to the case of Cd
2Re
2O
7, in which the
Hc2 is 0.29 T, much smaller than the corresponding Pauli’s limit. These distinct contrasts strongly suggest that the mechanism of superconductivity is essentially different between the two pyrochlore oxides.
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Shigeki Yonezawa, Yuji Muraoka, Zenji Hiroi
2004 Volume 73 Issue 7 Pages
1655-1656
Published: July 15, 2004
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The discovery of the new β-pyrochlore oxide superconductor CsOs
2O
6 with
Tc=3.3 K is reported. It is the third superconductor in the family of β-pyrochlore oxides, following KOs
2O
6 with
Tc=9.6 K and RbOs
2O
6 with
Tc=6.3 K. The
Tc of this series decreases with increasing ionic radius of alkaline metal ions, imposing a negative chemical pressure upon the Os pyrochlore lattice.
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Takashi Yasuda, Hiroaki Shishido, Taiki Ueda, Shin Hashimoto, Rikio Se ...
2004 Volume 73 Issue 7 Pages
1657-1660
Published: July 15, 2004
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We have studied the superconducting property by measuring the electrical resistivity under the magnetic field and pressure for CePt
3Si, which is the first antiferromagnetic heavy fermion superconductor without inversion symmetry in its tetragonal crystal structure. The upper critical field
Hc2(0) is found to be approximately isotropic:
Hc2(0)=2.7 T for
H||[100] and 3.2 T for
H||[001]. The Néel temperature
TN=2.3 K and the zero resistivity superconducting transition temperature
Tsc\\simeq0.65 K decrease markedly with increasing pressure, suggesting that the present superconductivity is correlated to the antiferromagnetic state.
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Takahiro Fukui
2004 Volume 73 Issue 7 Pages
1661-1664
Published: July 15, 2004
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A double-exchange model with quenched disorder for conduction electrons is studied by field theoretical methods. Using a path integral formalism and replica techniques based on it, an ensemble-averaged spin wave dispersion of localized spins is derived. It is shown that the spectrum of the spin wave has gaps at the multiple of the Fermi wave number of the conduction electrons in the presence of disorder, and hence, quenched disorder for electrons adds a striking effect to the dynamics of localized spins. In the strong disorder limit, the present results suggest a spin-glass-like behavior due to the frustration of the exchange coupling.
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Dai Aoki, Yoshiya Homma, Yoshinobu Shiokawa, Etsuji Yamamoto, Akio Nak ...
2004 Volume 73 Issue 7 Pages
1665-1668
Published: July 15, 2004
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We succeeded in growing a high-quality NpCoGa
5 single crystal by the Ga-flux method and measured its electrical resistivity, specific heat, magnetic susceptibility and magnetization. NpCoGa
5 is an antiferromagnet with a Néel temperature of 47 K. The magnetic moment of Np is directed along the [001] direction of a tetragonal crystal structure. A sharp metamagnetic transition was observed at
Hm=43 kOe for
H||[001], where the antiferromagnetic state is changed to the paramagnetic state above
Hm. The ordered moment was determined to be 0.74μ
B⁄Np. The magnetic properties were discussed on the basis of the crystalline electric field scheme of the 5
f4 configuration.
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Makoto Seto, Jobu Matsuno, Atsushi Fujimori, Takaya Mitsui, Yasuhiro K ...
2004 Volume 73 Issue 7 Pages
1669-1672
Published: July 15, 2004
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We have observed the extreme enhancement of elastic peak intensity in the energy spectrum of nuclear resonant scattering by
57Fe in CaFeO
3 following magnetic phase transition, while the inelastic scattering part of the spectrum hardly changed. This enhancement effect clearly indicates that the sum of the elastic and inelastic parts changes as the temperature changes, that is, it is not conserved. This effect is thought to be due to the change of the coherent scattering channel caused by the splitting of the nuclear energy level induced by magnetic phase transition without structural phase transition. This effect shows that the splitting in the energy ranges on the neV order emerges in the energy spectrum of the nuclear resonant scattering spectrum measured with the resolution function on the meV order. Therefore, the energy spectra of incoherent nuclear resonant scattering can be applied to the study of the phase transition of electronic states in addition to phonon states, and the origin of the phase transition will be distinguished clearly.
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Kazuhiro Marumoto, Yasuhito Muramatsu, Sota Ukai, Hiroshi Ito, Shin-ic ...
2004 Volume 73 Issue 7 Pages
1673-1676
Published: July 15, 2004
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Electron spin resonance (ESR) measurements are performed on field-induced carriers in regioregular poly(3-octylthiophene) (RR-P3OT) using metal–insulator–semiconductor (MIS) diode structures with RR-P3OT and Al
2O
3 as the active semiconductor and insulating layers, respectively. Clear ESR signals (
g∼2.002) are observed, which increase as the absolute value of the gate bias increases in the accumulation mode. The ESR signal is consistent with that of the photogenerated positive polarons in RR-P3OT detected by the light-induced ESR of RR-P3OT/C
60 composites, providing direct evidence that the field-induced carriers are polarons. Moreover, the molecular orientation of RR-P3OT’s in the diode structures, which is consistent with the self-organized lamellae reported, is confirmed by the anisotropy of the ESR signal.
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Takuji Nomura, Jun-ichi Igarashi
2004 Volume 73 Issue 7 Pages
1677-1680
Published: July 15, 2004
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We study theoretically the resonant inelastic x-ray scattering in quasi-one-dimensional insulating copper oxides, where the incident photon energy is tuned to the Cu 1
s–4
p absorption energy. Our attention is focused particularly on the strong momentum-transfer dependence of the spectral shape observed in recent experiments. We describe the antiferromagnetic ground state within the Hartree–Fock theory, and consider charge excitations from the ground state within the random phase approximation. By taking account of the electron correlation effects perturbatively, we obtain the detailed momentum-transfer dependence of the spectra in semiquantitative agreement with the experiments.
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Kozo Okada
2004 Volume 73 Issue 7 Pages
1681-1684
Published: July 15, 2004
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The electronic structure of quasi-one-dimensional nickelates, where the formal electron configuration of Ni ions is
d8, is discussed on the basis of numerically-exact diagonalization calculations of the O 1
s X-ray absorption spectrum (XAS) and X-ray emission spectrum (XES) using a four-site one-dimensional cluster model. In the undoped nickelate, the band dispersion along the chain direction is suppressed owing to the intra-atomic Coulomb interaction (
U) and Hund’s coupling (
J) on the Ni 3
d shell. As a result, the width of the O 1
s XAS peak that corresponds to the transition to the upper Hubbard band (UHB) is very narrow. Upon hole-doping, two new peaks that are split by
J appear about 2 eV below the UHB peak in accordance with the recent experiment of Y
2−xCa
xBaNiO
5. In the O 1
s XES of the undoped nickelate, we expect a peak that is caused by the spin exchange between neighboring Ni sites.
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Yukio Saito, Hiroyuki Hyuga
2004 Volume 73 Issue 7 Pages
1685-1688
Published: July 15, 2004
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To understand the chirality selection in the biological organic system, a simple lattice model of chemical reaction with molecular diffusion is proposed and studied by Monte Carlo simulations. In addition to a simple stochastic process of conversion between an achiral reactant A and chiral products, R and S molecules, a nonlinear autocatalysis is incorporated by enhancing the reaction rate from A to R (or S), when A is surrounded by more than one R (or S) molecules. With this nonlinear autocatalysis, the chiral symmetry between R and S is shown to be broken in a dense system. In a dilute solution with a chemically inactive solvent, molecular diffusion accomplishes chirality selection, provided that the initial concentration is higher than the critical value.
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Ning Wang, Miki Wadati
2004 Volume 73 Issue 7 Pages
1689-1698
Published: July 15, 2004
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We study τ-function representation of solutions and deformation of Hirota bilinear relations for a noncommutative Kadomtsev–Petviashvili (NC KP) hierarchy. An operator-valued τ-function representation of solutions for the NC KP hierarchy is presented. In contrast to the commutative case, the admissible τ-function satisfies an additional triangle-like relation. Furthermore, instead of the commutative Hirota bilinear relations, a set of triple-product relations such as Hirota triple-product differential/difference equations is found. Noncommutative deformation of multi-line soliton solutions of the NC KP hierarchy is also investigated. It is shown that for an arbitrary noncommutative parameter, the corresponding operator-valued τ-function in general is expressed in the form of infinite series.
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Hiroshi Iwasawa, Kuniaki Matsuo
2004 Volume 73 Issue 7 Pages
1699-1702
Published: July 15, 2004
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The exact solutions for the non-degenerate tow-photon Jaynes–Cummings model in the presence of the dynamic Stark-shifts are investigated. The Heisenberg equations of motion for the respective operators are established and the exact solutions are obtained. It will be shown how the presence of the Stark-shifts in the model influences the solutions of the operator differential equation.
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Yoshihito Ogasawara
2004 Volume 73 Issue 7 Pages
1703-1705
Published: July 15, 2004
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This paper discusses the flattening properties of the classical solution of the nonlinear evolution equation, which is derived from the model for the development of a solid surface controlled by the mechanism of evaporation–condensation under a vertical temperature gradient.
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Nobuhiko Saitô, Hironori Makino
2004 Volume 73 Issue 7 Pages
1706-1722
Published: July 15, 2004
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In contrast to the classical Hamiltonian mechanics whose chaotic behaviors are now well established, quantum mechanics is still obscure about the origin of its random behavior. It is shown in this paper that in case of the stadium billiard, the fact that the nodal lines are smooth but are randomly oscillating, as first described by Heller, and MacDonald and Kaufman, can be interpreted as due to the irregular pseudochaotic behavior of the phase. To do this, we employ the path integral representation of propagator and the reinterpreted Bohm’s formulation of quantum mechanics. Thus we reach the conclusion that although the chaotic behavior in quantum mechanics is suppressed by the Einstein quantization condition, it is observed in the properly defined phase of the propagator, or of the wave function, as a pseudochaos. In other words quantum mechanics has the counterpart of classical chaos in the phase of the propagator, and consequently, the wave function is also, pseudochaotic (random) with respect to
q, but it does not exhibit exponential instability. The essential feature of quantum chaos manifests itself in the vanishings of the average of the wave function and the two-point correlation of the wave function at high energies. They are closely related to ergodicity and quantum measurement, and in particular new light will be shed on the measurement theory. The basic assumptions in the random matrix theory are discussed, confirming the universality of level spacing distribution.
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Hidetsugu Sakaguchi, Masako Ohtaki
2004 Volume 73 Issue 7 Pages
1723-1727
Published: July 15, 2004
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Dendrites with developed sidebranches are numerically studied with a coupled map lattice model. The competitive dynamics among sidebranches determines the shape of the envelope. The envelope has a parabolic shape near the tip of the dendrite and the envelope angle with respect to the main branch increases up to 45° finally. In an intermediate region, the envelope grows roughly in a power law, however, the exponent increases gradually as a function of the distance from the tip. The competitive dynamics among many branches is also observed in a unidirectional growth from a linear seed, and it is compared with the competitive dynamics of sidebranches.
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Chiaki Yamaguchi, Naoki Kawashima, Yutaka Okabe
2004 Volume 73 Issue 7 Pages
1728-1733
Published: July 15, 2004
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We propose an efficient method for Monte Carlo simulation of quantum lattice models by generalizing the method [Phys. Rev. E
66 (2002) 036704] proposed for classical models by the present authors. In particular, we derive an exact relation between the density of states and the microcanonical averages of some macroscopic quantities. The simulation method consists of the graph construction by the loop/cluster algorithm and the estimation of the density of states by the relation. While there may be a few variants for the graph construction, we consider the one proposed by Troyer
et al. [Phys. Rev. Lett.
90 (2003) 120201]. The performance of the method is examined for
S=1⁄2 antiferromagnetic Heisenberg chain, and compared with other algorithms.
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Riki Kawashima, Naoki Takigashira, Hiroshi Isoda
2004 Volume 73 Issue 7 Pages
1734-1737
Published: July 15, 2004
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Time series of electric property for the triglycine sulfate crystal were measured at temperatures, 50K≤
T≤324K on heating. The time series data were analyzed by both statistical and non-linear dynamical procedures. Nonlinear dynamical fluctuation was observed in the vicinity of the ferroelectric phase transition.
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K. Morita, K. Morimoto, D. Kaji, H. Haba, E. Ideguchi, J. C. Peter, R. ...
2004 Volume 73 Issue 7 Pages
1738-1744
Published: July 15, 2004
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The production and decay of
272111 has been investigated using a gas-filled recoil ion separator in irradiations of
209Bi targets with
64Ni beam at 320, 323 and 326 MeV. We have observed 14 α-decay chains in total, that can be assigned, on the basis of their time correlations, to subsequent decays from
272111 produced in the
209Bi(
64Ni,1n) reaction. The present result is the first clear confirmation for the discovery of
272111 and its α-decay products,
264Bh and
268Mt, reported previously by a GSI group. New information on their half-lives and decay energies as well as the excitation function is presented.
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Jun-Hoi Lee, Ki-Hong Kwon, Jae-Soo Shin
2004 Volume 73 Issue 7 Pages
1745-1747
Published: July 15, 2004
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The optogalvanic line shapes are observed in a commercial hollow cathode discharge tube containing neon buffer gas. Anomalous optogalvanic line shape is particular for transition originating from the 3P
2 (1S
5 in Paschen notation) metastable level of neon. The anomalous line shape is interpreted as being due to two competing atomic processes, which are the collisional ionization and the depletion of metastable atoms. When the competition is almost comparable at discharge current of 15 mA, the differences in the polarity and the magnitude of the optogalvanic signal of the transition result in the anomalous line shape.
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Rakesh Kumar Pandey, Deep Narayan Tripathi
2004 Volume 73 Issue 7 Pages
1748-1753
Published: July 15, 2004
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An analytic solution of Ornstein–Zernike (OZ) equation for the structure factor for plasmas has been obtained using Sogami–Ise (SI) potential amongst plasma particles that contains attractive tail at large distances. Pastore
et al.’s criterion and a characteristic feature of the pair interaction potential have helped in reaching to the final expressions. The calculated structure factors compare well with that obtained by using Pastore
et al.’s expressions derived with the Derjaguin, Landau, Verwey and Overbeek (DLVO) potential in case of H
+-plasmas. The excess energy per particle and the values of the compressibility determined with the help of the calculated structure factors in the limit of momentum transfer becoming zero have been reported.
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Jun-ichi Sakai, Takamasa Masuda, Igor Sokolov
2004 Volume 73 Issue 7 Pages
1754-1763
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We present numerical simulations of plasma jet formation by using a novel 2.5 dimension MHD code, employing the Artificial Wind concept which allows to construct simple upwind shock-capturing schemes. Firstly we investigate the formation process of a plasma jet by the collision of two shock waves propagating at some angle between the fronts and we compare our results with the theory. We found that there appear three cases for the jet formation: (1) Heat dominated, (2) Jet-Heat, and (3) Jet dominated case, depending on the parameters of the collision angle and the shock velocity. We also found that even in the case where the two flows behind the colliding shock fronts are both a sub-sonic, the super-sonic plasma jet still appears there. Next we investigate the generation process of super-sonic plasma jet during direct collision of two magnetic flux tubes. We found that super-sonic plasma jets appear in a wide range of parameters. From many parameter runs we concluded that there are three important physical parameters governing the condition of super-sonic jet formation, namely, the colliding velocity, the colliding angle and the density in the flux tubes. The most important condition among them is that the density in the colliding flux tubes exceeds about 50 times the background density. We also found that the super-sonic plasma jets can be generated through magnetic reconnection, when two magnetic flux tubes with densities about 9 times higher than their surround are colliding. Our findings will help to better understand the complicated dynamics of the solar transition region.
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Hiroki Hasegawa, Yukiharu Ohsawa
2004 Volume 73 Issue 7 Pages
1764-1774
Published: July 15, 2004
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Magnetohydrodynamic waves propagating obliquely to an external magnetic field are theoretically studied. There exist three different modes in the frequency regime lower than the electron cyclotron frequency. Linear dispersion relations of these modes are discussed in detail. Nonlinear properties of the magnetosonic wave, which is one of the three modes, are then investigated. Positron velocities accelerated in a magnetosonic solitary wave are also discussed.
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Takayoshi Ishimoto, Masanori Tachikawa, Miho Yamauchi, Hiroshi Kitagaw ...
2004 Volume 73 Issue 7 Pages
1775-1780
Published: July 15, 2004
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The isotope effect in Pd nanoparticles that absorb hydrogen or deuterium (i.e., H/D isotope effect) was studied experimentally and theoretically. First, the geometries (i.e., lattice parameters) of such Pd nanoparticles exposed to hydrogen or deuterium gas were measured by using X-ray powder diffraction to determine the lattice parameters. Then, the geometrical and electronic relaxations of Pd
nH
− and Pd
nD
− (
n=1–6) clusters, which modeled Pd nanoparticles exposed to hydrogen or deuterium gas, were calculated by using a multi-component molecular orbital (MC_MO) method, which uses first principles of quantum mechanics to account for the quantum effect of proton/deuteron. Experimental results from the diffraction patterns show that the bond distances of Pd nanoparticles exposed to hydrogen gas (and thus had absorbed hydrogen) were about 0.005 Å longer than those of exposed to deuterium gas. These results were confirmed by analytical results from the MC_MO calculation for Pd
nH
− and Pd
nD
− clusters. Therefore, the local geometrical changes due to the H/D isotope effect control the geometrical changes of the entire nanoparticle. Both the experimental and analytical results also show that the nanoparticle (cluster) size influences the extent of the H/D isotope effect on the geometrical changes. Based on the analytical results, the electronic charge densities are only slightly influenced by the H/D isotope effect.
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Mongi Amami, Abdelhamid Ben Salah
2004 Volume 73 Issue 7 Pages
1781-1785
Published: July 15, 2004
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The structural instability of the [NH
4−n(CH
3)
n]
2HgCl
4 group have been investigated. Consideration of different crystals of this family shows that the H-bonds, obviously, hinder the appearance of incommensurately modulation. The dependence of phase transition sequence from the sizes of cation and anion may be obtained only for crystal with simple cation. The appearance of H-bonds complicates the situation and, leads to gradual disappearance of IC phase in the A
2BX
4 family.
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Koh Saitoh, Tadahiro Yokosawa, Michiyoshi Tanaka, An Pang Tsai
2004 Volume 73 Issue 7 Pages
1786-1792
Published: July 15, 2004
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A structural change of an Al
72Ni
20Co
8 decagonal quasicrystal into the S1-type superlattice ordered phase has been observed at about 450°C by
in-situ high-resolution electron microscopy. The Al
72Ni
20Co
8 alloy, prepared by water quenching from 900°C, is composed of mirror-symmetric atom-clusters (
m-cluster) with a 2-nm diameter, which form the Penrose pentagon tiling with an edge length of 2.0 nm. It has been found that above 400°C, most of the
m-clusters transformed into fivefold-symmetric cluster (
f-cluster) and the arrangement of the
f-cluster formed the S1-type superlattice. It is considered that the formation of the S1 superlattice order is attributed to the disappearance of the 1.2-nm intercluster bond and to the preferential order of the sense of the
f-cluster, which takes opposite senses between the neighboring clusters with a 2-nm intercluster distance. The phason flip of the positions of the 2-nm atom-clusters, which was first reported by Edagawa
et al. [Phys. Rev. Lett.
85 (2000) 1674], has been observed with an atomic scale resolution. It has been found that the phason flip is caused by a flip between the fivefold-symmetry cluster and the mirror symmetric cluster. Structural models of the
m- and
f-clusters were reexamined.
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Shuichiro Miyata, Takashi Itoh, Yasuo Saruyama, Yoshinobu Kawasaki, Te ...
2004 Volume 73 Issue 7 Pages
1793-1797
Published: July 15, 2004
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The thermal and structural properties at normal and high pressures of vinylidene fluoride–trifluoroethylene (VDF/TrFE) copolymer crystals with VDF molar contents between 59 and 77% are examined using several types of thermal analysis systems as well as X-ray measurement. Although temperature changes in the crystal structures transform from a continuous [cooled phase (CP) to high-temperature phase (HP)] to a discontinuous one [low-temperature phase (LP) to HP] with increasing VDF molar content or external pressure for 65% VDF sample, the second-order phase transition does not appear but the transition from CP to LP occurs prior to the first-order phase transition from LP to HP. The sample with 65% VDF is composed of only CP, and LP suddenly appears in the 68% VDF sample and another LP is expected to exist in 71 and 77% VDF samples. The percolation theory may be used to explain such structural transformation which is very sensitive to VDF content.
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Shin-ichiro Yoshikawa, Kouichi Okunishi, Makoto Senda, Seiji Miyashita
2004 Volume 73 Issue 7 Pages
1798-1804
Published: July 15, 2004
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The selection of the ground state among nearly degenerate states due to quantum fluctuations is studied for the
S=1⁄2 XY-like Heisenberg antiferromagnets on the triangular lattice in the magnetic field applied along the hard axis, which was first pointed out by Nikuni and Shiba. We find that the selected ground state sensitively depends on the degree of the anisotropy and the magnitude of the magnetic field. This dependence is similar to that in the corresponding classical model at finite temperatures where various types of field induced phases appear due to the entropy effect. It is also found that the similarities of the selected states in the classical and quantum models are not the case in a two-leg ladder lattice, although the lattice consists of triangles locally and the ground state of this lattice in the classical case is the same as that of the triangular lattice.
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Takuya Yoshioka, Akihisa Koga, Norio Kawakami
2004 Volume 73 Issue 7 Pages
1805-1811
Published: July 15, 2004
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We investigate a frustrated Ising spin system on the garnet lattice composed of a specific network of corner-sharing triangles. By means of Monte Carlo simulations with the heat bath algorithm, we discuss the magnetic properties at finite temperatures. It is shown that the garnet spin system with the nearest-neighbor couplings does not exhibit any magnetic transitions, yielding the large residual entropy at zero temperature. We also investigate the effect of the long-range dipolar interaction systematically to determine the phase diagram of the Ising model on the garnet lattice. We find that there appear a variety of distinct phases depending on the cutoff length of the long-range interaction, in contrast to the pyrochlore spin-ice systems.
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Fumihito Shikanai, Junko Hatori, Masaru Komukae, Zbigniew Czapla, Tosh ...
2004 Volume 73 Issue 7 Pages
1812-1815
Published: July 15, 2004
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Heat capacity of glycinium phosphite was measured by adiabatic calorimetry in a temperature range from 90 K to 300 K. A λ-type anomaly characteristic of the second order phase transition was observed at 224.3 K (
TC). The jump of the heat capacity at
TC is estimated as Δ
c=7.1±0.2 J K
−1 mol
−1. The transition enthalpy and transition entropy were estimated as Δ
H=82.20±0.07 J mol
−1 and Δ
S=0.40±0.01 J K
−1 mol
−1 respectively. Thermal expansions of the crystal were also measured along the crystallographic
a,
b and
c axes using the strain gages. The volume thermal expansion shows clear anomaly at
TC. The jump of thermal expansion coefficient at
TC is estimated as Δα
v=−2.7±0.3×10
−5 K
−1.
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Yukio Saito
2004 Volume 73 Issue 7 Pages
1816-1826
Published: July 15, 2004
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The elastic lattice Green’s function for a simple cubic substrate with a semi-infinite thickness is obtained numerically in the isotropic case. This allows us to replace the bulk substrate by a single surface layer in the study of epitaxial adsorption. Its application to the homoepitaxial adsorption systems with various surface defects, as adatoms, steps or islands, results in the evaluation of their formation and interaction energies. Interactions approach to the asymptotic limit by the continuum elasticity theory even at short distances, except the step–step interaction. The latter has a large transient region before the final asymptotics sets in. This shows that the continuum elasticity is insufficient to describe the structural details of the atomic scale when forces are distributed over two atomic layers, such as, at the step edge.
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Masahide Sato, Tomonori Mori, Makio Uwaha, Yukio Hirose
2004 Volume 73 Issue 7 Pages
1827-1832
Published: July 15, 2004
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On a Si(001) vicinal face, where the direction of fast surface diffusion alternates on consecutive terraces, step bunching has been observed under direct current heating. By using a one-dimensional step model with drift of adatoms, we study growth laws of step bunches. If evaporation is negligible, the average number
N of steps in a bunch increases with time as
N∝
tβ with β\\lessapprox1⁄2. The growth exponent β weakly depends on the repulsive interaction potential between steps. When steps at a distance
l interact with the repulsive potential ζ∝1⁄
lν, the average step distance in a bunch
lb decreases as
lb∝
N−α with α≈3⁄2(ν+2). The exponents α and β are related as β≈1⁄(2+α). The simulation results are consistent with experiment if we take account of both logarithmic and ν=2 potentials, which are expected in this system. The growth rate of the bunch size with step-down drift is faster than that with step-up drift. If evaporation of adatoms is significant, the difference of the growth rate in the opposite drift directions becomes small. The apparent exponent β depends on the drift direction, and is larger with step-up drift.
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Masahito Mochizuki, Masatoshi Imada
2004 Volume 73 Issue 7 Pages
1833-1850
Published: July 15, 2004
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The origin of the antiferromagnetic order and puzzling properties of LaTiO
3 as well as the magnetic phase diagram of the perovskite titanates are studied theoretically. We show that in LaTiO
3, the
t2g degeneracy is eventually lifted by the La cations in the GdFeO
3-type structure, which generates a crystal field. This allows the description of the low-energy structure of LaTiO
3 by a single-band Hubbard model as a good starting point. The lowest-orbital occupation in this crystal field stabilizes the AFM(G) state, and well explains the spin-wave spectrum of LaTiO
3 obtained by the neutron scattering experiment. The orbital-spin structures for
RTiO
3 where
R=Pr, Nd and Sm are also accounted for by the same mechanism. We point out that through generating the
R crystal field, the GdFeO
3-type distortion has a universal relevance in determining the orbital-spin structure of the perovskite compounds in competition with the Jahn–Teller mechanism, which has been overlooked in the literature. Since the GdFeO
3-type distortion is a universal phenomenon as is seen in a large number of perovskite compounds, this mechanism may also play important roles in other compounds of this type.
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Masatoshi Imada
2004 Volume 73 Issue 7 Pages
1851-1863
Published: July 15, 2004
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Phenomenological theory of the Mott transition is presented. When the critical temperature of the Mott transition is much higher than the quantum degeneracy temperature, the transition is essentially described by the Ising universality class. Below the critical temperature, phase separation or first-order transition occurs. However, if the critical point is involved in the Fermi degeneracy region, a quantum critical point appears at zero temperature. The originally single Mott critical point generates subsequent many unstable fixed points through various Fermi surface instabilities induced by the Mott criticality characterized by the diverging charge susceptibility or doublon susceptibility. This occurs in marginal quantum-critical region. Charge, magnetic and superconducting instabilitites compete severely under these critical charge fluctuations. The quantum Mott transition triggers multi-furcating criticality, which goes beyond the conventional concept of multicriticality in quantum phase transitions. Near the quantum Mott transition, the criticality generically drives growth of inhomogeneous structure in the momentum space with singular points of flat dispersion on the Fermi surface. The singular points determine the quantum dynamics of the Mott transition by the dynamical exponent
z=4. We argue that many of filling-control Mott transitions are classified to this category. Recent numerical results as well as experimental results on strongly correlated systems including transition metal oxides, organic materials and
3He layer adsorbed on a substrate are consistently analyzed especially in two-dimensional systems. The mechanism of cuprate high-
Tc superconductivity is also discussed in the light of the present insight and interpreted from the multi-furcation instability.
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Ryota Sato, Takuma Ohashi, Akihisa Koga, Norio Kawakami
2004 Volume 73 Issue 7 Pages
1864-1869
Published: July 15, 2004
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We investigate a multi-orbital extension of the periodic Anderson model with particular emphasis on electron correlations including orbital fluctuations. By means of a linearized version of the dynamical mean-field theory, we compute the renormalization factor, the density of states, the spectral gap and the local correlation functions for a given set of the intra- and inter-orbital Coulomb interactions as well as the Hund coupling. It is found that when a certain condition is met for the intra- and inter-orbital interactions for
f electrons, orbital fluctuations are enhanced, thereby enlarging the Kondo insulating gap. This effect is suppressed in the presence of the Hund coupling. We also clarify how the Kondo insulator is continuously changed to the Mott insulator when electron correlations among conduction electrons are increased.
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Makoto Matsumoto, Maki Tokii, Shinya Wakoh
2004 Volume 73 Issue 7 Pages
1870-1874
Published: July 15, 2004
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An improvement of the linear tetrahedron method for the Compton profile calculation is proposed. Analytical formulae are given for the two dimensional integration of the Brillouin zone along an arbitrary scattering vector. Consequently, programming code becomes very simple and the calculation time is improvable about 70% faster. Although we examine to the cubic system in this work, this idea can be applied to the other structures similarly.
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Taizo Sasaki, Masao Arai, Takao Furubayashi, Takehiko Matsumoto
2004 Volume 73 Issue 7 Pages
1875-1880
Published: July 15, 2004
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The LDA band-structure calculations have been performed for the insulating triclinic phase of the thio-spinel compound, CuIr
2S
4, which appears below the metal–insulator transition temperature, 230 K. While the properties of transition-metal spinel compounds have been discussed with the electron correlation theory in many cases, we found that the electronic structure of CuIr
2S
4 can be analyzed within the band-structure theory. In the results we obtained the small energy gap at the Fermi energy with the magnitude comparable to the measured ones. It has been also shown that the calculated density of states can explain the experiments, such as the photo-emission and optical spectra. Although the charge ordering model was proposed in the previous studies, the charge segregation in the atomic scale was not observed within the present calculations.
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Abdul Hannan, Kazuaki Iwasa, Masahumi Kohgi, Toyotaka Osakabe, Hideaki ...
2004 Volume 73 Issue 7 Pages
1881-1887
Published: July 15, 2004
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Various properties of the strongly correlated electron system CeSb at ambient pressure as well as under high pressures have been investigated employing X-ray as a probe. The satellite peaks caused by the lattice modulation of CeSb in its AFP3 phase at ambient pressure have been analyzed successfully. The satellite peak intensity pattern was explained based on a model considering different effective ionic sizes and the scattering form factors for Γ
7 and Γ
8-like Ce
3+ ions which appear in the ordered phase. The wave function for the Γ
8-like Ce ion with larger moment was found almost the same as that of
Jz=5⁄2, which is consistent with the neutron diffraction experiment. At high pressures above about 1.9 GPa, rapid decrease of lattice constant was found below a certain critical temperature
TL, below which a sudden increase of electrical resistivity appears. This phenomenon can be explained by the formation of magnetic polaron state below this temperature.
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Yusuke Nishihara, Eugene Frankevich, Akihiko Fujii, Masanori Ozaki, Ka ...
2004 Volume 73 Issue 7 Pages
1888-1894
Published: July 15, 2004
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Picosecond time-resolved measurements utilizing a two-correlated-pulses technique have been applied for studying the temperature and electrical field strength dependences of second-order process responsible for the formation of free charge in poly(3-octylthiophene) (PAT8) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV). We have observed maximum photocurrent at the superposition of pulses (Δ
t=0), which originates from the formation of free charge carriers in the second-order process, and it was clarified that fast and delayed components of the lifetime of polaron pairs exist. The lifetime of thermalized or trapped polaron pairs (τ
delay) was shown to increase at low temperature and low electrical field strength. The fast-decaying component of a polaron pair with the lifetime τ
fast of about 10 ps, which is prescribed to pretrapped polaron pairs, is insensitive to temperature and electrical field strength changes. Polaron pairs with short intercharge distances became remarkable at low temperature and high electrical field strength. For photoluminescence intensity, we obtained the opposite property: quenching of the photoluminescence intensity was maximal at the superposition of the pulses (Δ
t=0). We clarified that exciton dissociation hardly contributed to second-order photocurrent.
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Tsuneya Ando, Koichi Akimoto
2004 Volume 73 Issue 7 Pages
1895-1901
Published: July 15, 2004
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Numerical calculations of the conductance are performed to study effects of short-range scatterers on a perfectly conducting channel in metallic carbon nanotubes existing unless the potential range of scatterers is smaller than the lattice constant. The perfect channel can easily be destroyed in the presence of small amount of short-range scatterers when there are several bands at the energy, while it is much more robust in the energy range of metallic linear bands.
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Tomoaki Takasaki, Toshikazu Ekino, Takahiro Muranaka, Takayuki Ichikaw ...
2004 Volume 73 Issue 7 Pages
1902-1913
Published: July 15, 2004
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Tunneling spectroscopy measurements on polycrystalline MgB
2 have been carried out with a break-junction technique. The observed spectra exhibit the multiple-gap feature, which can be expressed by the correlated two-gap model. From the conductance fittings at 4.2 K, the gap parameters can be classified into Δ
S=2.2±0.3 meV, Δ
M=6.0±1.5 meV, and Δ
L≅10 meV. All these gaps exist up to the same critical temperature
Tc. The Δ
M undergoes various ways of temperature dependence, which can be attributed to the proximity-induced gap. We have also observed the conductances showing the features of normal conducting and/or low-
Tc phases. Our tunneling data can be explained by the proximity effect combined with the bulk multiple-gap features.
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