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Hiroshi Tsukahara, Takeo Inami
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 2 Pages
319-321
Published: February 01, 1999
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We show that the continuum limit of the integrable XYZ spin-1/2 chainon a half-line gives rise to the boundary sine-Gordon theory using theperturbation method.
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Kazuhito Itoh
Subject area: Statistical physics and thermodynamics.
1999 Volume 68 Issue 2 Pages
322-325
Published: February 01, 1999
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We present exact ground states in spin models with orbital degeneracy in one and higher dimensions. A method to obtain the exact ground states of the models when the Hamiltonians are composed of the products of two commutable operators is proposed. For the case of the spin-1/2 model with two-fold degeneracy some exact ground states are given, such as the Valence-Bond (VB), the magnetically ordered, and the orbitally ordered states under particular parameter regimes. We also find models with the higher spin and degeneracy which have the new type VB ground states in the spin and the orbital sectors.
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Tomomi Tao, Kei–ichi Tainaka, Hiraku Nishimori
Subject area: Statistical physics and thermodynamics.
1999 Volume 68 Issue 2 Pages
326-329
Published: February 01, 1999
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To know the effect of local destruction of habitat, we perform thecontact process on a destructed lattice.This system exhibits a phase transition.It is found that the phase-transition point can be represented by a scaling law of mean-field theory.However, such a law never holdsfor steady-state density of species;this is because the local destruction leads to an increasedfragmentation of habitat.
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Masayuki Tokita, Sayaka Suzuki, Keiichi Miyamoto, Takashi Komai
Subject area: Equations of state, phase equilibria, and phase transitions.
1999 Volume 68 Issue 2 Pages
330-333
Published: February 01, 1999
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Pattern formation in a shrinking gel is studied using the confocal laser scanning microscope to reveal the time evolution of the spatial distribution of the polymer network in the gel. The polymer network is distributed uniformly in the gel at the early stage of bubble pattern formation. The distribution of the polymer network in the gel, however, rapidly changes with time. Finally, hollow bubbles are built up in the gel. This process occurs much faster than the cooperative diffusion of the gel.
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Takashi Manago, Teruo Ono, Hideki Miyajima, Kenji Kawaguchi, Mitsugu S ...
Subject area: Electronic structure and electrical properties of surfaces, interfaces and thin films.
1999 Volume 68 Issue 2 Pages
334-337
Published: February 01, 1999
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The Pd metal in the multilayer consisting of NiO and Pd exhibits ferromagnetism, due to the proximity effect between NiO and Pd, and has ferromagnetic order at distances greater than 35, Å from the interface. The magnetic moment of Pd atom at the interface is 0.59, μ
B/Pd and decreases with increasing distance from the NiO layer.
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Tetsuo Honma, Yoshinori Haga, Etsuji Yamamoto, Naoto Metoki, Yoshihiro ...
Subject area: Superconductivity.
1999 Volume 68 Issue 2 Pages
338-341
Published: February 01, 1999
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Neutron scattering experiments have been carried out for a heavy fermion superconductor URu
2Si
2. We found that the (1 0 0) magnetic Bragg peak intensity is reduced by 1--2 superconducting transition temperature of 1.15, K. This is direct evidence of the interplay between magnetism and superconductivity in URu
2Si
2.
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Yoshinori Haga, Yoshihiko Inada, Kenji Sakurai, Yoshihumi Tokiwa, Etsu ...
Subject area: Superconductivity.
1999 Volume 68 Issue 2 Pages
342-345
Published: February 01, 1999
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We succeeded in growing a high-quality single crystal of the heavyfermion superconductor UPd
2Al
3 and observed the de Haas-van Alphen(dHvA) oscillation in both the normal and superconducting mixed states. The dHvA frequency, which is proportional to a maximum cross-sectional areaof the electron Fermi surface labelled α, does not change inmagnitude between the normal and mixed states, while the cyclotron mass of5.7, m
0 in the normal state is reduced to 3.5, m
0 at 0.7, H
c2, and the corresponding Dingle temperature of 0.20, K in the normalstate is increased to 0.39, K at 0.7, H
c2. Here, H
c2 of 39, kOe is the upper critical field along the [0001]direction in the hexagonal structure.
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Yuji Furukawa, Shinji Wada, Tsuyoshi Kajitani, Shoichi Hosoya
Subject area: Magnetics resonances and relaxations in condensed matter; MÖssbauer effect.
1999 Volume 68 Issue 2 Pages
346-349
Published: February 01, 1999
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In the low-temperature tetragonal phase of antiferromagnetic La
2CoO
4 (T
N=270, K), we have observed a
59Co zero-field nuclear-magnetic-resonance spectrum that consists of three lines: two dominant well-discriminative lines at 195, MHz (Co
I) and 227, MHz (Co
II) of nearly equal intensity; and a fractional broad line in the 250 to 325, MHz range with a complicate structure. The former was assigned to the Co atoms with six nearest-neighbor oxygen atoms, and the latter to those with oxygen vacancies in the neighborhood generated by the oxygen nonstoichiometry. At low temperatures, the nuclear spin-lattice relaxation rate T
1-1 of both Co
I and Co
II increases in proportion to T
3, indicating that the system is in a long-range antiferromagnetic ordered state. With increasing temperature, T
1-1 of Co
I shows a divergence increase at T
C4=12, K, and that of Co
II exhibits a cusp at T
C4=12, K and the divergence increase at T
C3=50, K, respectively, which are suggestive of successive transitions of the spin structure. We conclude that the difference in the resonance frequency of Co
I and Co
II is caused by a difference in the transferred hyperfine and/or dipolar fields from the adjacent Co spins. An orbital ordering of the d
xy wave with q=0.25 is proposed to be the most plausible ground state of Co
2+ ions, which may give two inequivalent Co sites in the hyperfine field.
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Masaya Ishihara, Masao Ogata
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1999 Volume 68 Issue 2 Pages
350-353
Published: February 01, 1999
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The effect of a spin gap on the photoemission spectral functions is studied in the one-dimensional t-J
XXZ model. We find that spinon bands show up in the spectral functions but holon bands are obscured in the spin-gap cases. The reason for this is studied using a simple interpretation of the spectral functions, which is a convolution between the spectral function of spinless fermions and a spin excitation weight Z(Q). The spin gap suppresses the singularity of Z(Q), and as a result, only the holon bands are obscured. It is also shown that the spinon peaks lie along a cosine band and extend over the region |k|>k
F. Finally, the momentum-dependent critical exponents of the power-law singularity at the spinon bands are determined.
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Kenji Imai
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 2 Pages
355-359
Published: February 01, 1999
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In this paper the Kaup-Newell (KN) inverse scattering formulation are generalized, and a new Darboux transformation is introduced for it. Some Darboux covariant (1+1) dimensional soliton equations associated with the generalized KN formulation are derived systematically, which include not only the derivative nonlinear Schrödinger (DNLS), the modified KdV, the sine-Gordon and the massive Thirring equations but also some new nonlinear time evolution equations. Multi-soliton solutions of the DNLS equation are constructed in the determinant form using the Darboux transformation, which include some new solutions, such as quasi-periodic solutions and soliton solutions under the quasi-periodic backgrounds.
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Effat A. Saied, Reda G. Abd El–Rahman
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 2 Pages
360-368
Published: February 01, 1999
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The paper considers the general form of the porous Medium Equation f(x)u
t=(g(x)D(u)(u
x)
m)
x+H(u)u
x, where the probability density and flux obey the modified Fourier's law and the drift terms are not omitted. The conditions for invariance are applied to determine the functional forms of the arbitrary functions f, g and H which admit the symmetry reduction transformations. We have studied models depending on the functional form of D(u): 1-D(u)=u
n and 2-D(u)=e
nu. A catalogue of symmetry reduction, to ordinary differential equation ODE, is given to each system including its integrability.
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Hon–Wah Tam, Xing–Biao Hu, Dao–Liu Wang
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 2 Pages
369-379
Published: February 01, 1999
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Motivated by Hirota and Satsuma's results on their coupled KdV equation, two integrable coupled nonlinear systems are considered. One of them is a coupled Ito system. It is shown that the coupled Ito system is a special case of the (6,2)-reduction of the two component BKP hierarchy while the other coupled system can be obtained from the (5,1)-reduction of the two component BKP hierarchy. By using MATHEMATICA, we obtain the 3- and 4-soliton solutions of the coupled Ito system. In addition, starting from bilinear equations of the other coupled system, a Bäcklund transformation is found and nonlinear superposition formulae are established. Soliton solutions and rational solutions are also derived from these results.
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Kazuhiro Hikami, Rei Inoue
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 2 Pages
380-385
Published: February 01, 1999
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We investigate the integrable structure of thequantum Volterra model, which is a discretization of theKorteweg--de Vries equation.Based on Sklyanin's method we derive the Baxter equation, and thenclarify a role of the “fundamental transfer matrix”.We show that the fundamental transfer matrix also generates theintegrals of motionfor a lattice analogue of the sine--Gordon system.
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Rei Inoue, Kazuhiro Hikami
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 2 Pages
386-390
Published: February 01, 1999
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Studied arethe integrable difference-difference equations for the lattice W currents, which can be regarded as the full-discretized (reduced) KP equations.We find explicit forms ofthe time-discretization for the lowest equations of the hierarchyby making use of the relation with the Bogoyavlensky lattice.
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Hideaki Ujino, Miki Wadati
Subject area: Mathematical methods in physics.
1999 Volume 68 Issue 2 Pages
391-395
Published: February 01, 1999
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Applying a method developed by Takamura and Takano for thenonsymmetric Jack polynomial, we present the Rodrigues formula forthe nonsymmetric multivariable Hermite polynomial.
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Tomoo Katsuyama, Ken–ichi Nagata
Subject area: Statistical physics and thermodynamics.
1999 Volume 68 Issue 2 Pages
396-400
Published: February 01, 1999
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The time interval of successive water-drips from a faucet was examined over a wide range of the flow rate. The dripping interval alternately exhibits a stable state and a chaotic state as the flow rate increases. In the stable state, the volume of the drip is kept constant at fixed flow rates, and the constant volume increases with the flow rate. In the chaotic state, in addition to a mechanics that the drip is torn by its own weight, the vibration of the drip on the faucet takes part in the strange behavior of the interval.
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Katsumi Hagita, Hiroshi Takano
Subject area: Statistical physics and thermodynamics.
1999 Volume 68 Issue 2 Pages
401-407
Published: February 01, 1999
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Relaxation modes and rates of a single polymer chainconfined in a straight tube by repulsive wallsare studied by Monte Carlo simulations of the bond fluctuation model, where only the excluded volume interaction is taken into account.The relaxation modes and rates are estimatedby solving generalized eigenvalue problems forthe equilibrium time correlation matrices C
//i, j(t) = ‹ (z
i(t) - z
c(t)) (z
j(0) - z
c(0)) ›
c and C
⊥i, j(t) = ½‹ r
i⊥ (t) · r
j⊥ (0) ›
c, where z
i and r
i⊥ are the components of the position vector of the ith segmentparallel and perpendicular to the tube axis, respectively, and z
c is the parallel component of the center of mass of the polymer chain.For the parallel component, the behavior of the pth slowest relaxation rateλ
//p of a polymer chain of N segments agrees with the scaling prediction λ
//p ~= λ
b (gp/N)
2for gp/N << 1, where λ
b and g arethe slowest relaxation rate within each blob andthe number of segments per blob, respectively.The corresponding relaxation modes show the Rouse-like behavior.For the perpendicular components, the behavior of the pth slowest relaxation rate λ
⊥pis consistent with the scaling prediction{λ}
⊥p ~= λ
b for gp/N < 1.The behavior of the corresponding relaxation modes is consistent with the blob picture.
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Wei–Guo Jin, Takashi Wakui, Kenji Hasegawa, Hiroharu Saito, Tats ...
Subject area: Atomic spectra and interactions of atoms with photons.
1999 Volume 68 Issue 2 Pages
408-413
Published: February 01, 1999
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High-resolution laser spectroscopy in Sm I has been performed by using a tunable diode laser together with a highly collimated atomic beam. Hyperfine structures and isotope shifts of Sm isotopes have been measured for four transitions in the wavelength region of 636--687, nm; the largest isotope shift has been observed. Hyperfine constants A and B of
147Sm and
149Sm have been determined for six levels. By using the purest s
2-sp transition with the largest isotope shift, nuclear parameters λ, changes in mean-square nuclear charge radii δ ‹ r
2›, and nuclear deformation parameters δ ‹ β
2› have been derived and discussed.
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Young–lTak Chough
Subject area: Atomic spectra and interactions of atoms with photons.
1999 Volume 68 Issue 2 Pages
414-427
Published: February 01, 1999
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We modeled an atomic beam micromaser experiment [G. Rempe et al.: Phys. Rev. Lett. 58 (1987) 353] as well as a more recently reported cavity-QED experiment of a similar type [M. Brune et al.: Phys. Rev. Lett. 76 (1996) 1800] using the theory of quantum trajectories in order to see to what degree agreement between theory and experiment can be achieved. We compared our computations with the analysis based upon a “quantum theory of micromaser” [P. Filipowicz et al.: Phys. Rev. A 34 (1986) 3077] for the purpose of reliability check. We found rather nonnegligible differences between the results of theories and of experiments.
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Youichi Ogawa, Osamu Kujirai
Subject area: Atomic spectra and interactions of atoms with photons.
1999 Volume 68 Issue 2 Pages
428-433
Published: February 01, 1999
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Autoionization states of neutral lutetium atom (Lu I) were investigated using atomic beam and two-color two-step laser resonance ionization spectroscopy (RIS). The Lu I was excited to the 5d6s(
1D)6p
2D
3/2o (29607.98, cm
-1) and 6s
2(
1S)7p
2P
1/2o (29430.90, cm
-1) states by the first step excitation and their channels were studied for the autoionization states. Twelve dyes were used at the second step excitation. Eighty-six autoionization states were found through the former channel and 49 states through the latter channel. There were 102 even-parity autoionization states after the elimination of the overlap of the states and 98 were new ones. Their total angular momentum (J) values were estimated.
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Toshiyuki Takagi, Yosuke Kayanuma, Satoshi Tanaka
Subject area: Molecular spectra and interactions of molecules with photons.
1999 Volume 68 Issue 2 Pages
434-439
Published: February 01, 1999
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The effect of localization of core holes due to dephasing in the resonantx-ray emission spectrum is investigated theoretically by applying thestochastic theory to a simplified model of diatomic molecule.The x-ray emission spectrum from the occupied molecular orbitals iscalculated under the condition that the core electron is excited resonantlyto one of the unoccupied molecular orbitals.It is found that, as the relaxation time of the relative phase between theatomic wave functions of the core orbitals becomes short as compared withthe core hole lifetime, the parity-broken luminescence gains its intensityindicating the partial localization of the core hole.Although the dephasing in the outer orbitals also contributes to thesymmetry breaking, its influence is relatively small due to the motionalnarrowing effect.
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Sakir Erkoç, Turgut Bastug, Masaru Hirata, Shoichi Tachimori
Subject area: Studies of special atoms and molecules.
1999 Volume 68 Issue 2 Pages
440-445
Published: February 01, 1999
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Structural stability and energetics of uranium microclusters, U
n (n=3--13, , 27--137), have been investigated by molecular-dynamics simulations. An empirical modelpotential energy function has been parameterised for the uranium element byusing the dimer interaction potential energy profile of U
2, whichis calculated by relativistic density functional method. Stable structures ofthe microclusters for n=3--13 have been determined by molecular--dynamics simulation. It has been found that uranium microclusters prefer to form three--dimensionalcompact structures. Molecular--dynamics simulations have also been performedfor spherical uranium clusters with sizes n=27--137.
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Hideo Yahata
Subject area: Fluid dynamics.
1999 Volume 68 Issue 2 Pages
446-460
Published: February 01, 1999
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Thermal convection of air in two-dimensional vertical cavities is considered under the boundary conditions of the left and right vertical walls kept at different temperatures and the top and bottom horizontal walls subject to thermal insulation. Linear stability analysis of thermal convection is made with the aid of the Galerkin method in which the field variables are expanded in terms of Chebyshev polynomials and linear growth rates of steady states are computed using the QR algorithm. The results of the stability analysis for air with the Prandtl number 0.71 over the range of the cavity aspect ratio A from 1 to 10 show that with increase of the temperature difference between the two vertical walls the oscillatory motion first generated by the instability of steady convection is in the form of the Tollmien-Schlichting or the internal gravity waves according as A > 3.65 or A < 3.41 while for 3.41 < A < 3.65 the internal gravity waves are first generated after the preceding spatial flow transition of the hydraulic jump.
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Kenji Matsuo, Youichi Murakami
Subject area: Fluid dynamics.
1999 Volume 68 Issue 2 Pages
461-470
Published: February 01, 1999
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Linear stability of Bénard-Marangoni convection in two-layer system is analyzed theoretically. Special attention is paid to the effect of the Biot number in both rigid boundaries and the thickness of the upper gas layer on the critical Marangoni number and the critical wavenumber. The deformation of interface is assumed to be neglected for linearizing the basic equation to the quiescent state. On the assumption of the exchange of stabilities, the eigenvalue problem for the neutral Marangoni number is derived, the analytical expression of the neutral curve and the linear modes are presented and the condition for the long-wave instability is discussed based on the structure of the mode.
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Daisuke Gyobu, Jun–ichi Sakai, Masanori Eda, Torsten Neubert, Mi ...
Subject area: The physics of plasmas and electric discharges.
1999 Volume 68 Issue 2 Pages
471-477
Published: February 01, 1999
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Using a two-dimensional electromagnetic and relativistic particle code, we show that electromagnetic waves can be emittedfrom Langmuir waves generated by an electron beam instability in pairplasmas. It is confirmed that the presence of a magnetic field isessential for the emission mechanism of the electromagnetic waves. The lineargrowth rate of the generation of electromagnetic waves is studied by manyparameter runs changing theelectron beam density, the electron beam velocity and the intensity ofmagnetic field. The plasma maser process is the most possible emissionmechanism of the electromagnetic waves.
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Takuya Iwasaki, Sanae–I. Itoh, Masatoshi Yagi, Kimitaka Itoh, Ul ...
Subject area: The physics of plasmas and electric discharges.
1999 Volume 68 Issue 2 Pages
478-486
Published: February 01, 1999
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A new model equation which includes the non-local effectin the heat flux is introduced to study the transient transportphenomena. A non-local heat flux, which is expressed in terms of theintegral equation, is superimposed on the conventional form of theheat flux. This model is applied to describe theexperimental results from the power switching [U. Strothet al.: Plasma Phys. Control. Fusion 38 (1996) 1087] and thepower modulation experiments [L. Giannone et al.:Nucl. Fusion 32 (1992) 1985] in the W7-AS stellarator.A small fraction of non-local component in the heat fluxis found to be very effective in modifying the response against anexternal modulation. The transient feature of the transport property, which are observed in the response of heat pulse propagation, arequalitatively reproduced by the transport simulations based on thismodel. A possibility is discussed to estimate thecorrelation length of the non-local effect experimentally by use ofthe results of transport simulations.
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Tomoya Isoshima, Kazushige Machida
Subject area: Mechanical and acoustical properties of condesed matter.
1999 Volume 68 Issue 2 Pages
487-492
Published: February 01, 1999
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The stability of a quantized vortex state in Bose-Einstein condensationis examined within Bogoliubov theory for alkali atom gases confined in a harmonic potential under forced rotation.By solving the non-linear Bogoliubovequations coupled with the Gross-Pitavskii equation, the elementary excitations and the totalenergy of the systems are calculated as a function of rotation velocity.There are two distinct criteria of vortex stability;The position of the excitation energy levels relative to the condensate energy levelyields the local stability criterion, andthe total energy relative to that ofthe non-vortex stateyields the global stability criterion.The vortex stability phase diagram in the rotation velocity vs theparticle density of the system is obtained, allowing one to locate the appropriate regionto observe the singly quantized vortex.
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Jose Schneider, Horacio C. Panepucci, Maria C. dos Santos, Carlos A. M ...
Subject area: Lattice dynamics and crystal statistics.
1999 Volume 68 Issue 2 Pages
493-507
Published: February 01, 1999
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Bis(4-chlorophenyl)sulfone (BClPS) is one of the few organic molecular solids which exhibits a displacive normal-incommensurate phase transition involving spatial modulations of conformational parameters. In the present work, the room temperature phase of BClPS was taken as a prototype, in order to investigate the structural stability of a group of related solids. Lattice dynamics calculations were performed in order to detect possible soft mode instabilities in the phonon dispersion branches. An atomistic semiempirical approach was adopted in lattice calculations, in addition to a semirigid molecular model considering the possibility of coupling between lattice and low lying internal degrees of freedom. Also, free-molecule equilibrium structure and dynamics calculations were performed using ab initio 3-21G
* methods, to evaluate the extent of conformational distortions of the molecule in solid phase. The contribution of the internal potential and the molecular packing on the lattice instability of BClPS and related derivatives are discussed. The results suggest that a possible new group of unstable molecular solids with a common prototype packing at high temperature could be identified, in a situation resembling the A
2BX
4 family of ionic solids.
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Orie Umiguchi, Takeshi Inaoka, Masayuki Hasegawa
Subject area: Equations of state, phase equilibria, and phase transitions.
1999 Volume 68 Issue 2 Pages
508-514
Published: February 01, 1999
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A simple model is proposed for the equation of state of C
60 solid under pressure up to -- 12, GPa and used to analyze selected experimental data. The model consists of a semiempirical modification of the Girifalco potential and is constructed such that it complies with basic experimental results such as the volume change associated with the orientational order-disorder transition observed at 260, K under normal pressure. We primarily concentrate on the experimental data of Ludwig et al., which seem the most plausible at low pressure and are the most systematic at high pressure. It is shown that the model can actually be constructed to yield quite well the experimental result in the whole range of pressure.
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Masayoshi Itou, Shunji Kishimoto, Hiroshi Kawata, Makoto Ozaki, Hirosh ...
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 2 Pages
515-520
Published: February 01, 1999
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The coincidence measurement between the Compton scattered photonand the recoiled electron (X, , eX) provides direct information onthe three dimensional electron momentum density (3D-EMD).A new coincidence measurement system, which gives us the energyspectrum of the recoiled electron by the means of time of flight method, has been successfully developed. The obtained momentum spaceresolution of the 3D-EMD was 0.30 a.u., and thefeasibility of measuring the state-selective 3D-EMD has beendemonstrated by using an electron binding energy effect.The 3D-EMD of a graphite foil is compared with a theoretical bandcalculation, within a present statistical accuracy. The effectof multiple scattering of recoiled electrons was calculated by aMonte-Carlo simulation and the experimental data were compared with them.
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Keiichi Ohara, Katsurou Hanzawa, Kei Yosida
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 2 Pages
521-530
Published: February 01, 1999
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The metamagnetic behavior of CeRu
2Si
2 andthe non Fermi-liquid behavior of CeNi
2Ge
2are described by the periodic Coqblin-Schrieffer modelwith anisotropic c-f exchange interactionin the mean-field theory.Only the Kramers doublet of M
J=± 5/2for the 4f states of Ce ions is considered, for the case of which the density of quasi-particle stateshas singularity of | ω |
-1/2 around the effective f-level energy.In the asymmetric case applicable to CeRu
2Si
2, the chemical potential reaches the singularityat a finite magnetic field, at whichthe magnetization shows a metamagnetic-like increase.On the other hand, in the symmetric case applicable to CeNi
2Ge
2, the chemical potential is on the singularity at zero magnetic field, and non-Fermi-liquid-like behaviorsemerge in the susceptibility and the specific heat.
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Mikio Uruichi, Kyuya Yakushi, Yoshiro Yamashita
Subject area: Electron states in condensed matter.
1999 Volume 68 Issue 2 Pages
531-538
Published: February 01, 1999
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The polarized reflection spectrum indicates that the organic metal (BEDT-ATD)
2PF
6(THF) has a quasi-one-dimensional band structure with a narrow bandwidth of ca. 0.24, eV. The intra-HOMO-band transition of (BEDT-ATD)
2PF
6(THF) shows two broad peaks at ca. 1000, cm
-1 and 1700, cm
-1 which feature is quite different from the Drude-like metallic absorption. The vibronic bands interfering with this absorption band begin to grow as dips at 100, K, which means that the screw-axis symmetry of the space group P2
1/a is broken below 100, K. This broken symmetry is supported by the splitting of the Raman band of a charge-sensitive vibrational mode. It is suggested from the comparison with the thermopower's data that this structural change has no long-range-ordered modulation above 50, K. The intensity of some infrared-active vibrational modes is enhanced by the intra-molecular charge oscillation whose optical transition appears at 4600, cm
-1.
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Minoru Sasaki, Naoki Miyajima, Hiroshi Negishi, Wen–Xiu Gao, Mas ...
Subject area: Electronic transport in condensed matter.
1999 Volume 68 Issue 2 Pages
539-547
Published: February 01, 1999
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Magnetotransport measurements have been made for quasi-two-dimensional η -Mo
4O
11 crystals in its charge-density-wave (CDW) phases along the crystallographic a
*-, b-, and c-axes at low temperatures 0.3--4.2, K in magnetic fields up to 11, T. The diagonal components ρ
xx (or b-axis), ρ
yy (c-axis), and ρ
zz (a
*-axis) of the resistivity tensor are highly anisotropic (ρ
xx<ρ
yy<< ρ
zz; ρ
zz/ρ
xx-- 10
2). Computer simulations for the magnetic field dependence of ρ
xx, ρ
yy, and ρ
xy are made using a multicarrier model, in good agreement with the observations. From the in-plane anisotropy, we have estimated the anisotropic shape of the Fermi surfaces. These anisotropic properties are discussed by considering the characteristic crystal structure and conduction process via conducting and insulating layers along the z-axis. Furthermore, in view of the existing band model of this material and the data analyses, the observed quantum oscillations are not simply due to Shubnikov de-Haas oscillations but to some magnetic-field induced phase transition, as found for low-dimensional organic Bechgaard salts, the essence of which is the presence of hidden quasi-one-dimensional Fermi surface.
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Youichi Yanase, Kosaku Yamada
Subject area: Electronic transport in condensed matter.
1999 Volume 68 Issue 2 Pages
548-560
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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In this paper we point out that the anomalous transport phenomena in high-T
c cuprates are comprehensively understood on the basis of Fermi liquid theory by taking account of a strong anti-ferromagnetic spin fluctuation. We assume phenomenologically the spectrum of magnetic excitation from experiment and calculate the self-energy on the basis of the one loop approximation. We show that the T-linear term of damping rate, the momentum dependence of lifetime and the transformation of Fermi surface are important to explain the anomalous transport phenomena such as resistivity, Hall coefficient and c-axis resistivity. In particular, the strong spin fluctuation leads to the transformation of Fermi surface which leads to a form more appropriate to nesting. This effect plays an important role. At last we show that our theory is applicable to not only the normal state but also the pseudogap state.
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Takeshi Nakanishi, Tsuneya Ando
Subject area: Electronic transport in condensed matter.
1999 Volume 68 Issue 2 Pages
561-566
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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The transmission and reflection coefficients of a carbon nanotube with a scatterer are calculated in a tight-binding model.The result obtained in a k·p scheme is shown to be essentially valid, including the complete absence of back scattering for scatterers with range larger than the lattice constant, unless the strength of the potential becomes comparable to the band width.When the potential strength is comparable to the band width, a resonant enhancement of back scattering appears and the result becomes completely different from that in the k·p scheme.
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Katsuki Amemiya
Subject area: Electronic transport in condensed matter.
1999 Volume 68 Issue 2 Pages
567-575
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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The electron transport through the tunneling potentialin magnetic fields is studied.Systems that we consider are a two-terminal quantum wire with a potential anda four-terminal cross junction.The increase of the magnetic field suppresses the transmission of electronsand the conductance decreases rapidly with the magnetic field.The electron is totally reflected atcertain values of the magnetic field and we find that this phenomenonis attributed to the interference of subbands with complex wavenumbersin the tunneling region.In the four-terminal configuration, the calculated Hall resistance shows oscillation-like behavior and changes its sign repeatedly.The suppression of the transmission to the forward leadis again found in this configuration.The distribution of probability density and current densityin the tunneling barriers is also examined.
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Zyun F. Ezawa, Kenichi Sasaki
Subject area: Electronic transport in condensed matter.
1999 Volume 68 Issue 2 Pages
576-585
Published: February 01, 1999
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An improved composite-boson theory of quantum Hall ferromagnets is proposed.It is tightly related with the microscopic wave-function theory. Thecharacteristic feature is that the field operator describes solely thephysical degrees of freedom representing the deviation from the groundstate.It presents a powerful tool to analyze excited states within the lowest Landau level.Excitations include a Goldstone mode and nonlocal topological solitons.Solitons are vortices and Skyrmions carrying the U(1) and SU(2) topologicalcharges, respectively. Their classical configurations are derived fromtheirmicroscopic wave functions. The activation energy of one Skyrmion isestimated, which explains experimental data remarkably well.
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Nobuhisa Fujima, Shogo Sakurai
Subject area: Electronic structure and electrical properties of surfaces, interfaces and thin films.
1999 Volume 68 Issue 2 Pages
586-593
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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Magnetic properties of Co
N clusters for N=13-147 are discussed bycalculating the electronic states of the clusters with the localspin-density functional method. Two kinds of oscillatory behavior are observed in the magnetism of the Co clusters. First, the magnetic moment per atom oscillates with increasing the clustersize. This oscillatory size dependence is simulated by an electronic shellmodel, where the discreteness of the energy levels derived from4s/4p-electrons originates the oscillation. Second, the localmagnetic moment oscillates from the surface to the center of the clusters, that is, a large magnetic moment at the surface atomic shell decreases at the second shell, increases at the thirdshell and again decreases at the fourth shell from the surface. The local density of states of 3d electrons changes shell by shell, parallel to the oscillation of the local magnetic moment.
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Atsutaka Maeda, Hideaki Yasuda, Tetsuo Hanaguri
Subject area: Superconductivity.
1999 Volume 68 Issue 2 Pages
594-598
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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We investigated the magnetic-field dependence of penetration depth in the Meissner state in an electron-doped cuprate superconductor Nd
2-xCe
xCuO
4 with x = 0.16, to clarify the symmetry of the order parameter of the superconducting state of these materials.We found that the results are consistent with a gap with lines of nodes.Thus, it is speculated that the d
x2-y2 symmetry is common to all the cuprate superconductors, both for hole-doped and electron-doped materials.
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Ryusuke Ikeda, Kiyoshi Isotani
Subject area: Superconductivity.
1999 Volume 68 Issue 2 Pages
599-612
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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The ground states and the ordering behaviors on cooling in the liquid regime of vortices of a layered superconductor in fields parallel to the layers are theoretically examined using the lowest Landau level approximation for the Lawrence-Doniach model and neglecting randomness. The field-induced change of ground states is largely determined by the magnitude of Abrikosov factor β
A and the sign of shear energy in an assumed pinned hexagonal lattice. We find that, in a narrow field range below the stability region of the pinned rhombic solid with no vacant interlayer spacings, a waving structure suggested in a recent numerical simulation is indeed the true ground state, and that a thermal fluctuation correction to the mean field energy is necessary to stabilize other pinned hexagonal solids realizable in lower fields. It is shown by examining the ordering behaviors of vortices in the liquid regime with significant layering effect that the positional correlation in any situation with negligible magnetic screening tends to first develop in the direction parallel to the layers and perpendicular to the field, and concluded that the freezing to a pinned ground state occurs at any field through a single first order transition weakened by the intrinsic pinning effect in nonrandom case.
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Kenichi Katoh, Toshiro Takabatake, Isamu Oguro, Akira Ochiai, Akihiro ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 2 Pages
613-619
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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Measurements of resistivity ρ, Hall coefficient R
H, magnetic susceptibility χ, magnetization, specific heat C and magnetoresistance have been performed on the hexagonal ferromagnets CeTSb (T=Pd, , Pt) and the isostructural compounds LaTSb using single crystalline samples. Strong anisotropy in ρ, ρ
c>ρ
a, was observed for both the Ce compounds as well as the La compounds. However, R
H(T) for CeTSb does not exhibit strong anisotropy between H//a and H//c. The anisotropic behavior of χ (T) for the Ce compounds is well reproduced by the crystalline electronic-field model. The analysis of χ (T) suggests that the ferromagnetic exchange interaction along the c axis in CePdSb is much stronger than that in CePtSb. Magnetization measurements reveal that the saturated magnetic moments of 1.32, μ
B and 0.91, μ
B for CePdSb and CePtSb lie within the c plane in the ferromagnetic state. The C(T) for CePdSb shows a clear jump at T
C=17.5, K in addition to a broad peak around 10, K. These results suggest that one dimensional magnetic order along the c axis occurs in CePdSb at T
C=17.5, K and three-dimensional order develops only below 10, K. It is found that ρ
c increases below 8, K and 6, K for CePdSb and CePtSb, respectively, and R
H(H//a, I//c) also increases below 10, K for both compounds. Unlike usual ferromagnets, the transverse and longitudinal magnetoresistances in the ferromagnetic states are largely positive for H//a. These unusual transport properties may be ascribed to the anomalous spin dynamics in the ferromagnetic state of the present systems.
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Akimasa Sakuma
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 2 Pages
620-624
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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Heisenberg type exchange constants of the 3d transition metals are studied with the first principles calculations based on the multiple scattering theory within the force theorem. The results convince ourselves that the variation of the exchange constants of the 3d transition metals can be qualitatively explained mainly through the differences of the d electron concentration. The influences of the crystal structures on the exchange constants are quantitatively discussed with the calculated results.
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Wei Chen, Kazuo Hida, Hiroki Nakano
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 2 Pages
625-630
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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The one dimensional S=1/2 Heisenberg model with dimerization (1-j) and quadrumerization (δ) in the magnetic field is studied by means of the numerical exact diagonalization of finite size systems and the conformal field theory. It is found that the magnetization plateau at half of the saturation value exists for δ ≠ 0. For δ = 0, this model is described by the conformal field theory with central charge c=1 at this value of magnetization. The critical exponent ν which characterizes the δ-dependence of the width of the plateau is calculated using the level spectroscopy method. The j-dependence of the critical exponent ν is found to be non-monotonic and discontinuous at j = 0. The effective theory of the magnetization plateau is also presented for various limiting cases.
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Yutaka Moritomo, Arao Nakamura, Kenji Ohoyama, Masayoshi Ohashi, Kazum ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 2 Pages
631-636
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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Anisotropic magnetic and transport properties have been investigated for single crystals of (Nd
1-zLa
z)Sr
2Mn
2O
7.We have derived the magnetic phase diagram against the La concentration z and have found that the low-temperature state is of layered antiferromagnetic with alternating MnO
2-sheets.The reentrant-type charge-ordered state is observed in the limited z-region around z=1.0 due to the released Jahn-Teller distortion.We further investigated magnetotransport properties for these antiferromagnetic manganites, and have found a large negative magnetoresistance, e.g., ρ
c(H)/ρ
c(0)-- 0.86 and ρ
ab(H)/ρ
ab(0)-- 0.88 at μ
0H=1, T.
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Toshio Mizushima, Yosikazu Isikawa, Takanori Yasuda, Tomohiko Kuwai, J ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 2 Pages
637-641
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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The electrical resistivity, magnetization, specific heat andthermoelectric power measurements were performed on a NdNiAl
4 single crystal along the principalaxes of the orthorhombic cell. The easy axis of magnetization was parallel to the b axis below 20, K.The spin-flipping was observed at the magnetic field 4.4, T along the baxis at 2, K.The magnetic phase diagram was determined from the spin-flipping field.The huge magnetic anisotropy energy was estimated from the experiments of the magnetic susceptibility and magnetization.The energy gap newly occurred below T
N was observed in the electrical resistivity along the b axis.From this result we have speculated that a new magnetic periodicity is made along the b axis below T
N.The magnetic susceptibility for the principal axes wasdiscussed on the bases of the crystalline-electric-field and molecular-field theories.
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Akihisa Koga, Seiya Kumada, Norio Kawakami
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 2 Pages
642-649
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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We investigate low-energy properties of two-dimensional quantum spin systems with the ladder and plaquette structures, which are described by a generalized antiferromagnetic Heisenberg model with both of the bond and spin alternations.By exploiting a non-linear σ model technique and a modified spin wave approach, we evaluate the spin gap and the spontaneous magnetization todiscuss the quantum phase transition between the ordered and disordered states. We argue how the spin-gapped phase is driven to the antiferromagnetic phase in the phase diagram.
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Yoshitoshi Kida, Keisuke Tajima, Yoshio Shinoda, Kohki Hayashi, Hiroyu ...
Subject area: Magnetic properties and materials.
1999 Volume 68 Issue 2 Pages
650-654
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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A change of the c-lattice parameter of Dy which is induced by magnetic field along the easy direction of magnetization has been studied by X-ray diffraction in the temperature range of the helix phase. A discontinuous change of the c lattice parameter accompanying to the helix to fan or ferromagnetic transition has been observed below 170, K, but it becomes continuous change above 170, K to T
N. The lattice modulation with the same wave number as the magnetic modulation has been observed at the distorted helix phase, which can be explained in terms of magnetoelastic effect.
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Seiji Miyashita, Taro Yoshino, Akira Ogasahara
Subject area: Magnetics resonances and relaxations in condensed matter; MÖssbauer effect.
1999 Volume 68 Issue 2 Pages
655-661
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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We propose a direct numerical method to calculate the dynamicalsusceptibility, χ''(ω), in strongly fluctuating quantum systems, where the system is nonmagnetic but the exchange effect is very strong.We demonstrate this method by calculating ESR line shape χ''(ω) of the one dimensional antiferromagnetic Heisenberg model (S=1/2) andcomparing the results with those obtained by other methods and experiments.
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José–María Martín–Olalla, Jaime Del C ...
Subject area: Dielectric properties and materials.
1999 Volume 68 Issue 2 Pages
662-665
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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The decay of the permittivity of Rb
2ZnCl
4 is studied over ten days in the commensurate phase. No equilibrium state is actually found after an experience of twelve days. Assuming that the heating branch may represent the equilibrium state a three-component relaxation law is obtained with three different relaxation time. These relaxation times are connected to three different mechanisms of permittivity decay: six domain wall merging, pair annihilation and pinning to defects.
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Kozo Okada, Akio Kotani
Subject area: Optical properties and condensedmatter spectroscopy and other interactions of matter with particles and radiation.
1999 Volume 68 Issue 2 Pages
666-673
Published: February 01, 1999
Released on J-STAGE: October 01, 1999
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In order to investiaget the influence of Cu-Cu interaction on the Cu 2p core-level x-ray absorption spectrum of LaCuO
3, the Lanczos calculations are performed for (Cu
3O
16)
23- and (CuO
16)
29- cluster models. The Cu 2p XAS is calculated as a function of the charge-transfer energy (Δ) between the Cu 3d and O 2p states.With decreasing Δ, the spin state of the ground state changes from magnetic to nonmagnetic. Around the critical Δ, the main line of the XAS splits by about 1.5 eV, reproducing the experimental result of LaCuO
3 well. In such low Δ cases, half the valence holes occupy the O 2p states, mediating the strong Cu-Cu coupling, and the photoabsorption at a particular Cu site inevitably affects the electronic states around the neighboring Cu sites, in contrast to divalent Cu compounds. This inter-site coupling is enhanced, when the tetragonal distortion of CuO
6 units is small. In other owrds, the 3d orbital degeneracy is important in discussing the Cu 2p XAS of LaCuO
3.The Cu 2p photoemission spectrum is also calculated.
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