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Volume 74, Issue 9
Displaying 1-46 of 46 articles from this issue
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Shu-fang Deng, Da-jun Zhang, Deng-yuan Chen2005 Volume 74 Issue 9 Pages 2383-2385
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe nonisospectral Kadomtshev–Petviashvili (KP) equation is solved by the Hirota method and Wronskian technique. Exact solutions that possess soliton characters with nonisospectral properties are obtained. In addition, rational and mixed solutions are derived. We also obtain a new molecular equation that admits a solution in the Wronskian form.View full abstractDownload PDF (1115K) -
Kunihiko Kaneko2005 Volume 74 Issue 9 Pages 2386-2390
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSSeveral extensions of an iterated function system (IFS) are discussed as possible applications to abstract dynamics of units (molecules) with slowly relaxing internal states under frequent collisional interactions. It is found that an increase in the collision frequency leads to successive discrete states that can be analyzed as partial steps to form a Cantor set. By considering the interactions among the units, a self-consistent IFS is derived, which leads to the formation and stabilization of multiple such discrete states. The proposed mechanism, if it exists in a complex polymer under a crowded condition, allows for the kinetically induced formation of multiple states.View full abstractDownload PDF (801K) -
Takahiro Yabuuchi, Yuki Nakamoto, Katsuya Shimizu, Takumi Kikegawa2005 Volume 74 Issue 9 Pages 2391-2392
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSAn angular dispersive X-ray diffraction experiment on calcium metal (Ca) has been performed at high pressures up to 139 GPa. Ca forms a face-centered cubic (fcc) lattice at ambient conditions, transforms to a body-centered cubic (bcc) lattice at 20 GPa, and further transforms to a simple cubic structure at 32 GPa. We found the simple cubic phase in a wide pressure range, from 32 to about 109 GPa, and discovered a new high-pressure phase above 113 GPa.View full abstractDownload PDF (253K) -
Kensuke Inaba, Akihisa Koga, Sei-ichiro Suga, Norio Kawakami2005 Volume 74 Issue 9 Pages 2393-2396
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSMott transitions in the two-orbital Hubbard model with different bandwidths are investigated at finite temperatures. By means of the self-energy functional approach, we discuss the stability of the intermediate phase that has one orbital localized and the other itinerant; this phase is caused by the orbital-selective Mott transition (OSMT). It is shown that the OSMT realizes two different coexistence regions at finite temperatures in accordance with the recent results of Liebsch. We further find that a particularly interesting behavior emerges around the special conditions U=U′ and J=0, which includes a new type of coexistence region that has three distinct states. By systematically changing the Hund coupling, we establish the global phase diagram to elucidate the key role played by the Hund coupling on the Mott transitions.View full abstractDownload PDF (162K) -
Yoshiro Kakehashi, Peter Fulde2005 Volume 74 Issue 9 Pages 2397-2399
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSBy making use of the self-consistent projection operator method with high-momentum and high-energy resolutions, we find a kink structure in the quasiparticle excitation spectrum of the two-dimensional Hubbard model in the underdoped regime. The kink is caused by a mixing between the quasiparticle state and excitations with short-range antiferromagnetic order. We suggest that this might be the origin of the strong concentration dependence of the ‘kink’ found in La2−xSrxCuO4 (x=0.03–0.07).View full abstractDownload PDF (266K) -
Naoki Momono, Akihiro Hashimoto, Yasuo Kobatake, Migaku Oda, Masayuki ...2005 Volume 74 Issue 9 Pages 2400-2403
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe performed low-bias STM measurements on underdoped Bi2212 crystals, and confirmed that a two-dimensional (2D) superstructure with a periodicity of four lattice constants (4a) is formed within the Cu–O plane at T<Tc. This 4a×4a superstructure, oriented along the Cu–O bonding direction, is nondispersive and more intense in lightly doped samples with a zero temperature pseudogap (ZTPG) than in samples with a d-wave gap. The nondispersive 4a×4a superstructure was clearly observed within the ZTPG or d-wave gap, while it tended to fade out outside the gaps. The present results provide a useful test for various models proposed for an electronic order hidden in the underdoped region of high-Tc cuprates.View full abstractDownload PDF (715K) -
Yutaka Itoh, Chishiro Michioka, Kazuyoshi Yoshimura, Akihiko Hayashi, ...2005 Volume 74 Issue 9 Pages 2404-2407
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe report a 205Tl NMR study of vortex states in an aligned polycrystalline sample of an overdoped high-Tc superconductor, Tl2Ba2CuO6+δ (Tc∼85 K), at a magnetic field of 2 T along the c axis. We observed an imperfect vortex lattice, so-called Bragg glass, at T=5 K, the coexistence of vortex solid and vortex liquid between 10 and 60 K, and vortex melting between 65 and 85 K. No evidence for local antiferromagnetic ordering at vortex cores was found for our sample.View full abstractDownload PDF (173K) -
Kazuki Ohishi, Ikuya Yamada, Akihiro Koda, Wataru Higemoto, Shanta R. ...2005 Volume 74 Issue 9 Pages 2408-2412
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe report on the magnetic phase diagram of a hole-doped cuprate Ca2−xNaxCuO2Cl2, which is free from buckling of CuO2 planes, determined by muon spin rotation and relaxation. It is characterized by a quasi-static spin-glass-like phase over a range of sodium concentrations (0.05≤x≤0.12), which is held between the long-range antiferromagnetic (AF) phase (x≤0.02) and the superconducting phase where the system is nonmagnetic for x≥0.15. The obtained phase diagram qualitatively agrees well with that commonly found for hole-doped high-Tc cuprates, strongly suggesting that the incomplete suppression of the AF order for x>0.02 is an essential feature of the hole-doped cuprates.View full abstractDownload PDF (277K) -
Masashi Kosaka, Yoshiaki Kato, Chieko Araki, Nobuo Môri, Yoshiki ...2005 Volume 74 Issue 9 Pages 2413-2416
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe report the highest transition temperature of quadrupolar ordering [TQ] in YbAl3C3, where a distinct anomaly is observed by specific heat and ultrasonic measurements at 80 K. Magnetization measurements show only a very slight change and no magnetic or structural phase transitions can be observed by neutron diffraction measurements in this temperature range. Therefore, we believe that YbAl3C3 shows an antiferroquadrupolar ordering with the highest TQ found to date and is the first realization of this ordering beyond liquid nitrogen temperatures for rare-earth and actinide intermetallic compounds.View full abstractDownload PDF (531K) -
Effects of Randomness on Field-Induced Phase Transition in the Bond-Alternating S=1 Spin Chain NTENPShinichi Matsubara, Katsuaki Kodama, Masashi Takigawa, Masayuki Hagiwa ...2005 Volume 74 Issue 9 Pages 2417-2420
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe report novel effects of randomness in [Ni(N,N′-bis(3-aminopropyl)propane-1,3-diamine(μ-NO2)]ClO4 (NTENP), an S=1 bond-alternating linear antiferromagnet with a dimer-singlet ground state. 15N NMR spectra develop a continuum with sharply peaked edges at low temperatures, indicating a field-induced inhomogeneous staggered magnetization. We attribute this to random anisotropic interactions due to the disorder of NO2 groups. The field-induced antiferromagnetic transition exhibits a markedly anisotropic behavior. We propose that the incoherent magnetization below the critical field (Hc) is transformed into a coherent antiferromagnetic moment with a spatially fluctuating amplitude above Hc.View full abstractDownload PDF (355K) -
Hiroyuki Nakamura, Yoichi Muro, Saurav Giri, Junpei Umemura, Hisao Kob ...2005 Volume 74 Issue 9 Pages 2421-2424
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESS(La1−xYx)Mn4Al8 (0≤x≤1) is a very unique itinerant electron system, in which the spin pseudogap can be controlled continuously and nearly uniformly in a wide range of the gap width from Δ\\simeq250 to 500 K by the anisotropic volume shrinkage induced by the chemical pressure. The hydrostatic pressure on LaMn4Al8 also increases Δ but tends to fill the gap. The strong and anisotropic volume dependence of Δ strongly supports the idea that the origin of the gap formation is associated with the one-dimensional geometry of the Mn spin arrangement.View full abstractDownload PDF (449K) -
Takashi Hotta2005 Volume 74 Issue 9 Pages 2425-2429
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSIn order to clarify exotic multipole properties of filled skutterudites, we evaluate multipole susceptibility for n=1–5, where n is the local f-electron number, on the basis of a multiorbital Anderson model constructed using the j–j coupling scheme. For n=1, magnetic fluctuations dominate over low-temperature electronic properties, while for n=2 and 4, electronic states are dominated by both magnetic and quadrupole fluctuations. For n=3 and 5, octupole fluctuations are found to be significant, depending on the crystalline electric field potential. We discuss the possible relevance of the results to actual materials.View full abstractDownload PDF (170K) -
Ryoichi Kajimoto, Hidenori Mochizuki, Hideki Yoshizawa, Hiroshi Shinta ...2005 Volume 74 Issue 9 Pages 2430-2433
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSMagnon excitations have been investigated for PrMnO3 showing an A-type antiferromagnetic ordering and TbMnO3 forming a long-period spin ordering by inelastic neutron scattering. Combined with a result of LaMnO3 [K. Hirota et al.: J. Phys. Soc. Jpn. 65 (1996) 3736], the systematic data revealed that the ferromagnetic exchange interaction between nearest-neighbor (NN) Mn sites in the ab plane markedly decreases in RMnO3 with the ionic radius of R. In addition, finite next-nearest-neighbor (NNN) coupling is evident in TbMnO3. In contrast, the exchange interaction along the c axis shows a much weaker R dependence consistent with the Mn–O–Mn bond angle. These observations confirm a scenario that explains the evolution of spin structures in RMnO3 in terms of the competition between the NN and NNN interactions [T. Kimura et al.: Phys. Rev. B 68 (2003) 060403(R)].View full abstractDownload PDF (404K) -
Daisuke Okuyama, Takeshi Matsumura, Hironori Nakao, Youichi Murakami2005 Volume 74 Issue 9 Pages 2434-2437
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe have observed geometrical frustration of quadrupolar and magnetic moments in dysprosium tetraboride, DyB4, where the rare-earth sites form a Shastry–Sutherland lattice. Resonant X-ray scattering at the LIII absorption edge of Dy was utilized. Analysis of the energy, polarization, temperature, and azimuthal-angle dependences of the E1 resonance of the (1 0 0) forbidden reflection show that the magnetic and quadrupolar components within the frustrated c plane have a short-range correlation, suggesting that the moments are fluctuating. In contrast, the basic antiferromagnetic component along the c-axis has a long-range order.View full abstractDownload PDF (265K) -
Yoshihito Ogasawara, Katsuya Eda, Akihiko Kitada2005 Volume 74 Issue 9 Pages 2439-2442
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSAn essential factor causing the instability (stability) of a solid/liquid interface during solidification is explored. By examining the qualitative properties of the classical solution of a nonlinear evolution equation, the bifurcation, the coalescence and the growth rate of the interface are discussed. These discussions lead to the relation between the instability (stability) and the curvature of the interface.View full abstractDownload PDF (88K) -
Ryuji Ishizaki, Naoki Kodama, Masayoshi Inoue2005 Volume 74 Issue 9 Pages 2443-2448
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSA discrete-time dual random walk is presented whose random increment vn consists of the sum of the first stage random increments ui as vn≡|∑i=1n−1ui|γun. Our numerical study shows that its exponent ζ of the mean square displacement linearly depends on the parameter γ as ζ=1+γ. Critical phenomena is observed when ui is generated by iterated maps where the critical exponent α of the diffusion coefficient also linearly depends on the parameter γ as α=α0+cγ.View full abstractDownload PDF (1214K) -
Feng-Ling Yu, Yan-Hui Bi, Ying Zhai, Wei-Zhong Zhao, Ke Wu2005 Volume 74 Issue 9 Pages 2449-2452
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe motion of a discrete curve in Minkowski space is introduced, through which, the geometric equivalences between the discrete integrable modified Heisenberg ferromagnet (HF) models and integrable differential-difference equations are presented.View full abstractDownload PDF (76K) -
Hiromichi Goko2005 Volume 74 Issue 9 Pages 2453-2458
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSA simple Langevin model proposed by Büttiker and Landauer is analytically studied and numerically simulated. We start with calculating the probability current of our model analytically and show numerically that the fluctuation theorem is valid for our model. Then, a new approach to find the probability distribution is proposed. Finally, we investigate the characteristics of the probability distribution.View full abstractDownload PDF (105K) -
Yosuke Yoshimura2005 Volume 74 Issue 9 Pages 2459-2474
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSSolvophobic effects on an infinitely-thin hard needle in two-dimensional square-well fluids are studied with an analytical expansion and a Monte Carlo (MC) calculation on the chemical potential from the gaseous to liquid densities. The analytical expansion is made for a short needle with respect to the needle length. The solvophobic effects on an extremely short needle is correlated with those on the radial distribution function between solvent disks at the contact distance. The solvophobic solvation on a short needle is exothermic, i.e., the chemical potential of the needle decreases with the increase in the solvent–solvent interaction, at low densities, while it is endothermic at high densities. The solvophobic interaction between short needles can be attractive or repulsive depending on the configuration of the interacting needles as well as the density region of the fluid. The solvophobic effects on a hard needle of finite length are evaluated by a MC method through the free-path distribution of a small and light particle in the square-well fluid. The MC calculation shows that the solvophobic solvation is exothermic even at high densities, when the needle is sufficiently long. The exothermic behavior is apparently due to a long range component evolved with the elongation of the needle. The solvophobic interaction at high densities changes its characteristics with the needle length also.View full abstractDownload PDF (1233K) -
Chiyori Urabe2005 Volume 74 Issue 9 Pages 2475-2479
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe investigate the fluctuation of the top location of a sandpile numerically using the two-dimensional discrete elements method. We feed particles to a sandpile at a fixed time interval and calculate power spectra from the time series of the top location. We find that the power spectra are approximated as power functions, and their exponents increase to −1 through a plateau as the time interval decreases. For small time interval, avalanches occur continuously either on the left or right side slope of a sandpile, and the slope on which avalanches take place switches intermittently. The long time fluctuation of the top location corresponds to the switchings. For the time series of the switchings, we discuss the relation between the power spectrum and the distribution of waiting times based on analytic theories.View full abstractDownload PDF (298K) -
Sachiko Oshima, Takeshi Nihei, Takehisa Fujita2005 Volume 74 Issue 9 Pages 2480-2486
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe nucleon EDM is shown to be directly related to the EDM of atomic systems. From the observed EDM values of the atomic Hg system, the neutron EDM can be extracted, which gives a very stringent constraint on the supersymmetry parameters. It is also shown that the measurement of Nitrogen and Thallium atomic systems should provide important information on the flavor dependence of the quark EDM. We perform numerical analyses on the EDM of neutron, proton and electron in the minimal supersymmetric standard model with CP-violating phases. We demonstrate that the new limit on the neutron EDM extracted from atomic systems excludes a wide parameter region of supersymmetry breaking masses above 1 TeV, while the old limit excludes only a small mass region below 1 TeV.View full abstractDownload PDF (206K) -
Tomoaki Ohtsuka, Nobuo Nishimiya, Takako Fukuda, Masao Suzuki2005 Volume 74 Issue 9 Pages 2487-2491
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe Doppler-free two-photon spectra of the 6S1⁄2(F=3)–6D3⁄2(F=2 to 5), 6S1⁄2(F=4)–6D3⁄2(F=2 to 5), 6S1⁄2(F=3)–6D5⁄2(F=5 to 1) and 6S1⁄2(F=4)–6D5⁄2(F=6 to 2) transitions in cesium are observed using a titanium-sapphire laser. These spectra can be used as an optical frequency standard. The hyperfine coupling constants A (magnetic dipole constant) and B (electric quadrupole constant) are determined using spectral line splittings, giving A=16.17(17) MHz and B=0.11(127) MHz for the 6D3⁄2 state, and A=−4.56(9) MHz and B=−0.35(183) MHz for the 6D5⁄2 state.View full abstractDownload PDF (213K) -
Qin Yang, Chaoqing Dai, Yueyue Wang, Jiefang Zhang2005 Volume 74 Issue 9 Pages 2492-2495
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe have investigated the quantum Zakharov equations and the existence of quantum solitons in the fully nonlinear quantum wave. For simplicity, we use the so-called sech and tanh expansion method, and obtain several new quantum solitary wave solutions, such as the bright soliton, gray soliton, W-soliton and M-soliton. In contrast to the classical Zakharov equations, in the case of quantum Zakharov equations, the terms proportional to H2 modified the dispersion-nonlinearity equilibrium, which is the ultimate responsible for the existence of solitons. Furthermore, changing H may affect the nature of the solutions in a fundamental way. In addition, some properties of the quantum solitons that we obtained in the fully nonlinear quantum waves are different from those in the weakly nonlinear limit [F. Haas et al.: Phys. Plasmas 10 (2003) 3858].View full abstractDownload PDF (93K) -
Hiroshi Iwasaki, Ken-ichi Ohshima2005 Volume 74 Issue 9 Pages 2496-2500
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThis paper describes a unified interpretation of unusual short-range order diffuse scattering intensity distribution, the appearance of intensity maxima simultaneously at the special points L and X of the reciprocal space, and of the formation of a variety of long-range ordered structures, including less common structures, in the face-centered cubic Cu–Pt alloys. Reassessment is first made of the ordered structures on the Pt-rich composition side and then it is shown that all the structures in the alloys are systematically described adopting the static concentration wave model, originally developed by Khachaturyan, with the two kinds of waves, L11 wave and L12 wave, and their combination. These waves are assumed to be still alive at temperatures above the order–disorder transition point with appreciably decreased amplitude and coherency length and lead to the appearance of the two types of diffuse intensity maxima. Comparison is made with the ordering behaviors in the well-known Cu–Au alloys, in which ordered structures forming are described simply by the L12 waves and diffuse intensity maxima appear only at the X point and its equivalent positions. Discussion is made on the difference between the Cu–Au and Cu–Pt alloys taking into account of the uniqueness of Pt as an alloying element.View full abstractDownload PDF (225K) -
Xiang He, Ling-Ti Kong, Bai-Xin Liu2005 Volume 74 Issue 9 Pages 2501-2505
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSEmploying ab initio calculations, the relative stabilities of the possible crystalline structures at compositions of CoTa3, Co3Ta and CoTa were predicted and based on thermodynamic calculations, the possible structural phase transitions were predicted over a broad composition range for the metastable crystalline Co–Ta alloys. To confirm the relevance of the calculations, ion-beam-mixing experiments were conducted using Co–Ta multilayered films with various overall compositions. It turned out that the experimentally observed formation of metastable crystalline Co–Ta phases agreed reasonably well with the theoretical predictions and that the glass-forming range of the Co–Ta system was determined to be within 25–70 at. % of Ta, matching fairly well with that estimated from thermodynamic calculations. Moreover, a reverse martensitic phase transformation was observed in the CoTa2 multilayers upon ion irradiation. In addition, steady-sate thermal annealing of the Co–Ta multilayered films also provided some evidence in support to the ab initio and thermodynamic calculations.View full abstractDownload PDF (134K) -
Kiyoshi Deguchi, Shinji Azuma, Yuki Kobayashi2005 Volume 74 Issue 9 Pages 2506-2509
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe pressure–temperature (p–T) phase diagram of the hydrogen-bonded ferroelectric CsD2PO4 (DCDP) was studied by measurements of the dielectric constant. Two pressure-induced phases (phase III and phase IV) were observed. The phase III is an antiferroelectric phase stable at 0.65GPa<p<1.05GPa. The phase IV is a new phase stable at p>1.05 GPa, which is probably the other antiferroelectric (antiferrodistortive) phase. The temperature and pressure dependences of the dielectric constant were analyzed on the basis of the quasi-one-dimensional model. The results were compared with the results of CsH2PO4 (CDP) reported previously.View full abstractDownload PDF (569K) -
Ryuichi Okamoto, Youhei Fujitani2005 Volume 74 Issue 9 Pages 2510-2516
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSLower vacancy-density in a crystalline solid slows down the tracer diffusion via the vacancy-assisted mechanism, which can be modeled by means of particles hopping to their respective nearest-neighbor lattice-sites stochastically with double occupancy prohibited. The explicit expressions of the diffusion coefficient were previously obtained for various lattices in terms of Nakazato and Kitahara’s method [Prog. Theor. Phys. 64 (1980) 2261]. This method yields a set of linear simultaneous algebraic equations as many as the number of lattice sites, which is reduced to a simple equation with respect to the diffusion coefficient in the final step of the method. We here give a systematic way of the reduction in terms of the group theory.View full abstractDownload PDF (138K) -
Osamu Sakai, Yukihiro Shimizu, Yasunori Kaneta2005 Volume 74 Issue 9 Pages 2517-2529
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe band calculation scheme for f electron compounds is developed on the basis of the dynamical mean field theory (DMFT) and the LMTO method. The auxiliary impurity problem is solved by a method named as NCAf2v’, which includes the correct exchange process of the f1→f2 virtual excitation as the vertex correction to the non-crossing approximation (NCA) for the f1→f0 fluctuation. This method leads to the correct magnitude of the Kondo temperature, TK, and makes it possible to carry out quantitative DMFT calculation including the crystalline field (CF) and the spin–orbit (SO) splitting of the self-energy. The magnetic excitation spectra are also calculated to estimate TK. It is applied to Ce metal and CeSb at T=300 K as the first step. In Ce metal, the hybridization intensity (HI) just below the Fermi energy is reduced in the DMFT band. The photo-emission spectra (PES) have a conspicuous SO side peak, similar to that of experiments. TK is estimated to be about 70 K in γ-Ce, while to be about 1700 K in α-Ce. In CeSb, the double-peak-like structure of PES is reproduced. The HI is enhanced just at the Fermi energy in the DMFT band of CeSb. Therefore, TK∼60 K, which is comparable to but slightly larger than the experimental value, is obtained.View full abstractDownload PDF (458K) -
Annamária Kiss, Yoshio Kuramoto2005 Volume 74 Issue 9 Pages 2530-2537
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe nature of multiple electronic orders in skutterudite PrFe4P12 is discussed on the basis of a model with antiferro-quadrupole (AFQ) interaction of Γ3 symmetry. The high-field phase can be reproduced qualitatively provided (i) ferro-type interactions are introduced between the dipoles as well as between the octupoles of localized f-electrons, and (ii) separation is vanishingly small between the Γ1–Γ4(1) crystalline electric field (CEF) levels. The high-field phase can have either the same ordering vector q=(1,0,0) as in the low-field phase, or a different one q=0 depending on the parameters. In the latter case, distortion of the crystal perpendicular to the (111) axis is predicted. The corresponding anomaly in elastic constants should also appear. The electrical resistivity is calculated with account of scattering within the CEF quasi-quartet. It is found that the resistivity as a function of the direction of magnetic field shows a sharp maximum around the (111) axis at low temperatures because of the level crossing.View full abstractDownload PDF (165K) -
Atsushi Yamasaki, Akira Sekiyama, Shin Imada, Masanori Tsunekawa, Clau ...2005 Volume 74 Issue 9 Pages 2538-2543
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe bulk and surface electronic structures of Sm4As3 have been investigated by hard and soft X-ray photoemission spectroscopies (PESs). PES with a wide range of photon energies (hν’s) between 220 and 2450 eV demonstrates the absence of valence mixing in both high- and low-temperature phases, that is, the valence of Sm ions is definitely trivalent in the bulk and divalent on the surface. Atomic multiplet calculations taking into account the bulk and surface spectral weights at each hν well reproduce the experimental valence band PES and Sm 3d core-level spectra, supporting the valence difference between bulk and surface in Sm4As3.View full abstractDownload PDF (185K) -
Kenji Yonemitsu2005 Volume 74 Issue 9 Pages 2544-2553
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSTo clarify the mechanism of recently reported, ambipolar carrier injections into quasi-one-dimensional Mott insulators on which field-effect transistors are fabricated, we employ the one-dimensional Hubbard model attached to a tight-binding model for source and drain electrodes. To take account of the formation of Schottky barriers, we add scalar and vector potentials, which satisfy the Poisson equation with boundary values depending on the drain voltage, the gate bias, and the work-function difference. The current–voltage characteristics are obtained by solving the time-dependent Schrödinger equation in the unrestricted Hartree–Fock approximation. Its validity is discussed with the help of the Lanczos method applied to small systems. We find generally ambipolar carrier injections in Mott insulators even if the work function of the crystal is quite different from that of the electrodes. They result from balancing the correlation effect with the barrier effect. For the gate-bias polarity with higher Schottky barriers, the correlation effect is weakened accordingly, owing to collective transport in the one-dimensional correlated electron systems.View full abstractDownload PDF (678K) -
Akira Oguri, Yunori Nisikawa, A. C. Hewson2005 Volume 74 Issue 9 Pages 2554-2562
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe describe a formulation to deduce the phase shifts, which determine the ground-state properties of interacting quantum-dot systems with the inversion symmetry, from the fixed-point eigenvalues of the numerical renormalization group (NRG). Our approach does not assume the specific form of the Hamiltonian nor the electron–hole symmetry, and it is applicable to a wide class of quantum impurities connected to noninteracting leads. We apply the method to a triple dot which is described by a three-site Hubbard chain connected to two noninteracting leads, and calculate the dc conductance away from half-filling. The conductance shows the typical Kondo plateaus of the Unitary limit g\\simeq2e2⁄h in some regions of the onsite energy εd, at which the total number of electrons Nel in the three dots is odd, i.e., Nel\\simeq1, 3 and 5. In contrast, the conductance shows a wide minimum in the regions of εd corresponding to even number of electrons Nel\\simeq2 and 4. We also discuss the parallel conductance of the triple dot connected transversely to four leads, and show that it can be deduced from the two phase shifts defined in the two-lead case.View full abstractDownload PDF (581K) -
H. Watanabe, Y. Kobayashi, M. Sato2005 Volume 74 Issue 9 Pages 2563-2567
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe superconducting state of NaxCoO2·yH2O with three CoO2 layers in a unit cell has been studied by 59Co-NMR. The Knight shift measured for a peak of the NMR spectra corresponding to the external magnetic field H along one of the principal directions within the CoO2 plane, exhibits a rapid decrease with decreasing temperature T below the superconducting transition temperature Tc, indicating that the spin susceptibility χspin is suppressed in the superconducting phase, at least, for this field direction. Because differences of the superconducting properties are rather small between this three-layer NaxCoO2·yH2O and previously reported NaxCoO2·yH2O with two CoO2 layers within a unit cell, the present result of the Knight shift studies indicates that the Cooper pairs of the former system are in the singlet state as in the latter, for which the spin susceptibility is suppressed for both directions of H parallel and perpendicular to the CoO2 plane.View full abstractDownload PDF (275K) -
Youichi Yanase, Masahito Mochizuki, Masao Ogata2005 Volume 74 Issue 9 Pages 2568-2578
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe d-vector in possibile spin triplet superconductor NaxCoO2·yH2O is microscopically investigated on the basis of the multi-orbital Hubbard model including the atomic spin–orbit coupling. As a result of the perturbation theory, we obtain the stable spin triplet superconductivity where the p-wave and f-wave states can be stabilized. If we neglect the spin–orbit coupling, superconducting state has 6-fold (3-fold) degeneracy in the p-wave (f-wave) state. This degeneracy is lifted by the spin–orbit coupling. We determine the d-vector within the linearlized Dyson–Gorkov equation. It is shown that the d-vector is always along the plane when the pairing symmetry is p-wave, while it depends on the parameters in case of the f-wave state. The lifting of degeneracy is significant in the p-wave state while it is very small in the f-wave state. This is because the first order term with respect to the spin–orbit coupling is effective in the former case, while it is ineffective in the latter case. The consistency of these results with NMR and μSR measurements are discussed.View full abstractDownload PDF (197K) -
Seiichiro Onari, Ryotaro Arita, Kazuhiko Kuroki, Hideo Aoki2005 Volume 74 Issue 9 Pages 2579-2585
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe pairing symmetry in the electron mechanism for superconductivity is explored when charge fluctuations coexist with spin fluctuations. The extended Hubbard model is adopted to obtain, with the fluctuation exchange approximation, a phase diagram against the on-site Coulomb repulsion U and the off-site repulsion V for a square lattice with a second-neighbor hopping t′. We have observed the following. (i) For large U(>9), a triplet superconductivity with sin(kx+ky) symmetry can appear just below the charge density wave phase. The pairing is degenerate with sin(kx−ky), so a chiral sin(kx+ky)+isin(kx−ky) that breaks the time-reversal symmetry should result, which is a candidate for the gap function on the γ band of Sr2RuO4 and is consistent with a recent measurement of the specific heat. (ii) By systematically deforming the Fermi surface with varied t′, the region most favored by the triplet is identified to be the region where the Fermi surface traverses the van Hove singularity with the charge susceptibility strongly enhanced.View full abstractDownload PDF (1126K) -
Tomoaki Takasaki, Toshikazu Ekino, Hironobu Fujii, Shoji Yamanaka2005 Volume 74 Issue 9 Pages 2586-2591
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSBreak junction tunneling spectroscopy measurements have been carried out on the novel layered nitride superconductor ZrNCl1−x (x≅0.3) with Tc=12–14 K. Two kinds of gap structures are reproducibly observed, both of which can be described by the BCS density of states. Values of the gap parameters at 4 K are obtained to be Δ=1.6–2.3 meV and 4.0–5.1 meV. Upon warming, these gap structures disappear at Tc, thereby giving the ratio 2Δ⁄kBTc=2.7–3.8 and 6.6–8.4, respectively. The former is within the value of conventional superconductors, while the latter is extremely large in comparison with that of the conventional strong-coupling superconductors. The larger ratio is similar to the value of high-Tc cuprates. The origins of such two kinds of gaps are discussed.View full abstractDownload PDF (325K) -
Shogo Shinkai, Hiroaki Ikeda, Kosaku Yamada2005 Volume 74 Issue 9 Pages 2592-2597
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe investigate the normal selfenergy and the mass enhancement factor in the Hubbard model on the two-dimensional square lattice. Our purpose in this paper is to evaluate the mass enhancement factor more quantitatively than the conventional third order perturbation theory. We calculate it by expanding perturbatively up to the fourth order with respect to the on-site repulsion U. We consider the cases that the system is near the half-filling, which are similar situations to high-Tc cuprates. As results of the calculations, we obtain the large mass enhancement on the Fermi surface by introducing the fourth order terms. This is mainly originated from the fourth order particle–hole and particle–particle diagrams. Although the other fourth order terms have effect of reducing the effective mass, this effect does not cancel out the former mass enhancement completely and there remains still a large mass enhancement effect. In addition, we find that the mass enhancement factor becomes large with increasing the on-site repulsion U and the density of state (DOS) at the Fermi energy ρ(0). According to many current reseaches, such large U and ρ(0) enhance the effective interaction between quasiparticles, therefore the superconducting transition temperature Tc increases. On the other hand, the large mass enhancement leads the reduction of the energy scale of quasiparticles, as a result, Tc is reduced. When we discuss Tc, we have to estimate these two competitive effects.View full abstractDownload PDF (131K) -
Koichi Hiraoka, Yasuhiro Sasaki, Shoichi Tomiyoshi2005 Volume 74 Issue 9 Pages 2598-2603
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSZero-field 59Co NMR, X-ray diffraction (XRD) and magnetization measurements have been made to investigate the mechanical alloying (MA) of ferromagnetic Co30M70 (M=Cu, Ag and Au) powder as a function of milling time (MT). The MA in Co30Cu70 proceeds rapidly with increasing MT by both the processes of dissolving Cu in the Co matrix and Co in the Cu matrix and is nearly completed for MT=100 h. In Co30Ag70 the MA hardly proceeds even for MT=300 h or more. The MA in Co30Au70 proceeds much more slowly than that in Co30Cu70 with increasing MT up to 150 h and takes place rapidly for MT≈200 h. The magnetizations and NMR spectra of the Co30Cu70 and Co30Au70 samples for MT=200 h are similar to each other, indicating that both the samples form similar supersaturated alloys. NMR results of the Co30M70 samples milled for MT=200 h show large spin fluctuations of Co atoms, which are due to fine sizes of clusters, suggesting that the samples milled for long times consist of nanometer-size clusters.View full abstractDownload PDF (691K) -
Noriki Terada, Setsuo Mitsuda, Toru Fujii, Ken-ichiro Soejima, Ikuo Do ...2005 Volume 74 Issue 9 Pages 2604-2611
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe have performed magnetic susceptibility, neutron diffraction and specific heat measurements on the triangular lattice antiferromagnet CuFe1−xAlxO2 for x≤0.050. A magnetic phase diagram for temperature vs x was determined. The various magnetically ordered phases compete with each other on the x–T magnetic phase diagram, strongly suggesting that the quasi-Ising orderings are stabilized in CuFeO2 with delicate balance of competing interactions. In the ground state for 0.014<x<0.030 [low-temperature (LT) phase], the magnetic structure consists of two magnetic modulations with slightly different wave numbers. Moreover, we observed the change in magnetic diffraction patterns in the LT phase, which corresponds to a crystallographic distortion from “hexagonal” to “orthorhombic”, suggesting that the Ising anisotropy in CuFeO2 is closely related to the crystallographic distortion.View full abstractDownload PDF (455K) -
S. Yoshii, M. Fujita, N. Takamoto, K. Kindo, Y. Echizen, T. Takabatake2005 Volume 74 Issue 9 Pages 2612-2616
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSThe effect of magnetic field on the pseudogap in the Kondo semimetal CeNiSn has been reinvestigated by the measurement of magnetization and longitudinal magnetoresistance in pulsed high magnetic fields applied along the principal crystallographic directions of the orthorhombic structure. By extending the field range up to 65 T, metamagnetic behaviors at 45 and 60 T are observed for the first time along the easy magnetization direction of a-axis. No anomaly is found, on the other hand, along the b- and c-axes up to 55 T. The magnetoresistance along the a-axis exhibits the minimum at about 30 T and increases above 40 T, which is in accord with the anomalous increase of the magnetization. By contrast, the magnetoresistance along the b- and c-axes shows only a monotonous decrease above 10 T. These results are discussed in terms of a Zeeman splitting of the double-gapped density of states derived from the anisotropic hybridization-gap model.View full abstractDownload PDF (234K) -
Arumugam Thamizhavel, Hiroshi Nakashima, Tomoyuki Shiromoto, Yoshiko O ...2005 Volume 74 Issue 9 Pages 2617-2621
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe report the resistivity, magnetic susceptibility, magnetization and specific heat studies on a single crystal of CePdSb3 which crystallizes in the orthorhombic crystal structure. CePdSb3 behaves as a Kondo lattice compound in which Ce moments order antiferromagnetically below 3.1 K, in contrast to the previously published polycrystal data. The magnetic susceptibility is highly anisotropic, reflecting the orthorhombic crystal structure. The magnetization for H||[001], which corresponds to the easy axis, shows a metamagnetic transition at 1.6 kOe and saturates above 10 kOe, reaching a value of 1.6 μB/Ce. The magnetization for H||[010] also shows a metamagnetic transition at 11 kOe, while the magnetization H||[100] increases linearly as a function of magnetic field, indicating a hard axis.View full abstractDownload PDF (489K) -
Masataka Iinuma, Yoshiro Takahashi, Ippei Shaké, Masahiro Oda, ...2005 Volume 74 Issue 9 Pages 2622-2630
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe have carried out detailed systematic studies of relaxation effects, which contribute to a significant improvement in proton polarization in a single crystal of naphthalene doped with pentacene. The experiments have been performed in a magnetic field of 3 kG at room temperature or at 77 K and with a pulsed dye laser or a pulsed N2 laser. We have found that a relaxation rate in the presence of irradiation with visible light (λ=595 nm) is much smaller than that with ultraviolet light (λ=337 nm) at room temperature, although the absorption rate of visible light is much larger than that of ultraviolet light. By cooling the crystal, the slow motion of the naphthalene molecules, which is a dominant relaxation process, can be suppressed. Surprisingly, we have found that the relaxation time at 77 K in the presence of the dye laser becomes long, but still depends on the laser power. Our investigation has also indicated that both the longer relaxation time and the irradiation with the dye laser lead to a great improvement in the polarization of protons in the bulk of a crystal from 0.5% at room temperature to 32% at 77 K.View full abstractDownload PDF (272K) -
Kenji Suzuki, Kaoru Yamamoto, Kyuya Yakushi, Atsushi Kawamoto2005 Volume 74 Issue 9 Pages 2631-2639
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSWe present the optical conductivity and Raman spectra of θ-(BEDT-TTF)2CsZn(SCN)4. The vibrational and vibronic bands in the 1200–1600 cm−1 region was assigned with the aid of the 13C-substituted compound. The nearly uniform charge distribution was found in a whole temperature range from 300 to 6 K. However, the space group symmetry I222 is locally broken already at room temperature. The broken symmetry suggests the resemblance to the high-temperature phase and frozen state of θ-(BEDT-TTF)2RbZn(SCN)4, which consists of short-range ordered charge-ordering domains. The amplitude in the charge-ordering domain of θ-(BEDT-TTF)2CsZn(SCN)4 is extremely small in a whole temperature range. At room temperature, hydrostatic pressure narrows the bandwidth of θ-(BEDT-TTF)2CsZn(SCN)4 to enlarge the amplitude in short-ranged ordered domains. The long-range ordered charge ordering in θ-(BEDT-TTF)2CsZn(SCN)4 was found at 10 K under the hydrostatic pressure of 2.5 GPa.View full abstractDownload PDF (818K) -
T. Yamagata, S. Nakayama, M. Tanaka, T. Itahashi2005 Volume 74 Issue 9 Pages 2640-2641
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSDownload PDF (73K) -
Kiyosi Terao2005 Volume 74 Issue 9 Pages 2642-2643
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSDownload PDF (53K) -
Yuuichi Tazuke, Yoshihiro Ohta, Satoshi Miyamoto2005 Volume 74 Issue 9 Pages 2644-2645
Published: September 15, 2005
Released on J-STAGE: January 24, 2008
JOURNAL RESTRICTED ACCESSDownload PDF (70K)
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