巻号一覧
77 巻, 4 号
選択された号の論文の34件中1～34を表示しています
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Hiroyasu Matsuura, Kazumasa Miyake2008 年 77 巻 4 号 p. 043601
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありSoftening of elastic constants in non-doped and B-doped Si with a vacancy is discussed theoretically on the basis of a numerical diagonalization study. To explain the difference of the magnetic field dependence of the elastic constant between B-doped Si and non-doped Si, it is crucial to take the spin–orbit coupling into account. As a result, taking also the many body effect, we explain the experiments on the softening of elastic constants so far, and predict that the softening ceases at the temperarture of the order of mK in non-doped Si with the high magnetic field of 10 T.抄録全体を表示PDF形式でダウンロード (149K) -
Fuminori Honda, Marie-Aude Measson, Yasunori Nakano, Naohisa Yoshitani ...2008 年 77 巻 4 号 p. 043701
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありA layered compound CePd5Al2, which is an analog of a heavy fermion superconductor NpPd5Al2, is found to be an antiferromagnet with an easy-axis along the tetragonal [001] direction but becomes superconductive in the pressure region from 9 to 12 GPa, with the superconducting transition temperature, Tsc=0.57 K and the upper critical field at 0 K, Hc2(0)=2.5 kOe, at 10.8 GPa. The quasi-two dimensional Fermi surfaces are also theoretically calculated for CePd5Al2 on the basis of the 4f-itinerant band model.抄録全体を表示PDF形式でダウンロード (1635K) -
Katsunori Kubo2008 年 77 巻 4 号 p. 043702
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありWe propose that in a system with pocket Fermi surfaces, a pairing state with a finite total momentum qtot like the Fulde–Ferrell–Larkin–Ovchinnikov state can be stabilized even without a magnetic field. When a pair is composed of electrons on a pocket Fermi surface whose center is not located at Γ point, the pair inevitably has finite qtot. To investigate this possibility, we consider a two-orbital model on a square lattice that can realize pocket Fermi surfaces and we apply fluctuation exchange approximation. Then, by changing the electron number n per site, we indeed find that such superconducting states with finite qtot are stabilized when the system has pocket Fermi surfaces.抄録全体を表示PDF形式でダウンロード (121K) -
Yasuko Tarui, Yoshiaki Kobayashi, Masatoshi Sato2008 年 77 巻 4 号 p. 043703
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありMagnetization and 7Li-NMR measurements have been carried out for an a-axis-aligned sample of Li2ZrCuO4, which has quasi one-dimensional Cu2+ spins (s=1⁄2) in chains of edge-sharing CuO4 square planes and exhibits the magnetic transition at temperature TN∼7 K. The NMR results at ∼2 K indicate that the system has an incommensurate helical order of Cu spins within the ac-plane. Although the ferroelectricity is predicted in this ordered state by existing theories developed for a single chain, no anomalies have been observed in the dielectric susceptibility ε and electric polarization P for polycrystalline samples.抄録全体を表示PDF形式でダウンロード (368K) -
Kiyotaka Miyoshi, Yuta Takaichi, Yusuke Takamatsu, Motonobu Miura, Jun ...2008 年 77 巻 4 号 p. 043704
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありPressure dependence of superconducting transition temperature Tc has been determined through the DC magnetic measurements under pressure up to P=10 GPa for β-pyrochlore oxides AOs2O6 with A = Cs (Tc=3.3 K), Rb (6.3 K), and K (9.6 K). Both for A = Rb and Cs, Tc increases with increasing P and shows a saturation at Tcm∼8.8 K, which is considered as the upper limit of Tc inherent in AOs2O6. In contrast, the Tc–P curve for KOs2O6 shows a sharp maximum of ∼10 K at P∼0.5 GPa, and Tc is higher than Tcm for 0≤P≤1.5 GPa, suggesting the enhanced superconductivity due to the rattling of K ions.抄録全体を表示PDF形式でダウンロード (314K) -
Akira Sugimoto, Toshikazu Ekino, Hiroshi Eisaki2008 年 77 巻 4 号 p. 043705
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありThe atomically resolved local barrier height (LBH) of a Bi2Sr2CaCu2O8+δ (Bi2212) superconducting single crystal is investigated by using scanning tunneling microscopy/spectroscopy (STM/STS). The LBH distribution is found to be strongly related with the well-known supermodulation structure of the Bi2212 surface with a period of ∼2.7 nm. In particular, the magnitude of the LBH is anticorrelated to the Bi–Bi atomic distance that is affected by supermodulation. A comparison with simultaneously obtained conductance spectra shows that there is a small correlation between the spatial modulation of the gap amplitude (Δ) and the LBH, this indicates that the measured Δ is slightly affected by the topmost BiO surface, but dominantly reflects information on the inner CuO2 layer, which is responsible for the superconductivity.抄録全体を表示PDF形式でダウンロード (11077K) -
Aya Tamura, Katsuhiro Maeda, Gaku Motoyama, Yasukage Oda2008 年 77 巻 4 号 p. 043706
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありExchange-enhanced paramagnetic compound TiCo has recently been found to become superconducting at 35 mK. We have measured the electrical resistivity, specific heat, and magnetization in the normal state of a newly prepared polycrystalline TiCo whose superconducting transition temperature is 45 mK in comparison with that whose transition temperature is 35 mK. The electrical resistivity shows a linear relationship with T2 at low temperatures and a nearly linear relationship with T at high temperatures. Specific heat is interpreted as the sum of the contributions of electron spin fluctuations and lattice vibrations above approximately 2.0 K. The magnetization shows a linear relationship with magnetic field above 1000 Oe, which is in agreement with previous reports. The results agree with the calculations based on the spin fluctuation theory.抄録全体を表示PDF形式でダウンロード (165K) -
Katsuhiro Morita, Midori Yano, Toshio Ono, Hidekazu Tanaka, Kotaro Fuj ...2008 年 77 巻 4 号 p. 043707
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありWe investigated the crystal structure of Rb2Cu3SnF12 and its magnetic properties using single crystals. This compound is composed of Kagomé layers of corner-sharing CuF6 octahedra with a 2a×2a enlarged cell as compared with the proper Kagomé layer. Rb2Cu3SnF12 is magnetically described as an S=1⁄2 modified Kagomé antiferromagnet with four kinds of neighboring exchange interaction. From magnetic susceptibility and high-field magnetization measurements, it was found that the ground state is a disordered singlet with the spin gap, as predicted from a recent theory. Exact diagonalization for a 12-site Kagomé cluster was performed to analyze the magnetic susceptibility, and individual exchange interactions were evaluated.抄録全体を表示PDF形式でダウンロード (451K) -
Akira Hara, Yuhei Natsume2008 年 77 巻 4 号 p. 043708
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありBy numerical calculation for the three-band Hubbard model, we investigate the role of the difference between interorbital and intraorbital interactions in alkali-metal-doped C60, AxC60 (A = K, Rb, etc.). In order to explain the observed optical conductivity, the consideration of the difference is essential. In fact, A2C60 and A4C60 lose the metallic conductivity such as Drude weight with decreasing intraorbital interaction under the condition of constant interorbital interaction: In spite of the decrease in total correlations, the metallic behavior disappears. In contrast, A3C60 retains its metallic behavior. These reasons are made clear on the basis of the change in the electronic configurations in the ground states.抄録全体を表示PDF形式でダウンロード (216K) -
Hiroshi Murakawa, Yoshinori Onose, Kenya Ohgushi, Shintaro Ishiwata, Y ...2008 年 77 巻 4 号 p. 043709
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありApplication of magnetic field (H) can produce the ferroelectric polarization (P) in a proper screw helimagnet, ZnCr2Se4. While rotating H, we observed the cyclic generation of polarization current arising from the change of P in the conical spin structure. Versatile variations of P in magnitude and sign are observed while changing the direction and magnitude of H. The behaviors are ascribed to the rotation of the spin cones and the conserving or reversing spin-helicity upon the flop of the screw propagation vector, as affected by the competition among the magnetic anisotropy, inclination of the cone axis to H, and the P domain-wall stability.抄録全体を表示PDF形式でダウンロード (2959K) -
Eric M. Heatwole, Oleg V. Prezhdo2008 年 77 巻 4 号 p. 044001
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありWe derive a semi-classical Langevin equation that, in conjuction with a quantum fluctuation–dissipation theorem, can be used to run canonical dynamics and to determine thermal averages in the second-order quantized Hamilton dynamics (QHD-2). In contrast to our earlier work [J. Chem. Phys. 122 (2005) 234109], the bath is no longer treated classically, and the friction is represented at the second-order. As a result, the quantum fluctuation variables are kept close to their optimal values, similarly to the recently developed phase-space canonical averaging for QHD-2 [J. Chem. Phys. 126 (2007) 204108]. The theory is exact for the quantum harmonic oscillator and the free particle, and gives good agreement with the quantum answer for a variety of quartic potentials.抄録全体を表示PDF形式でダウンロード (497K) -
Jun Ohkubo, Nadav Shnerb, David A. Kessler2008 年 77 巻 4 号 p. 044002
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありWe study a simple chemical reaction system and effects of the internal noise. The chemical reaction system causes the same transition phenomenon discussed by Togashi and Kaneko [Phys. Rev. Lett. 86 (2001) 2459; J. Phys. Soc. Jpn. 72 (2003) 62]. By using the simpler model than Togashi–Kaneko’s one, we discuss the transition phenomenon by means of a random walk model and an effective model. The discussion makes it clear that quasi-absorbing states, which are produced by the change of the strength of the internal noise, play an important role in the transition phenomenon. Stabilizing the quasi-absorbing states causes bifurcation of the peaks in the stationary probability distribution discontinuously.抄録全体を表示PDF形式でダウンロード (221K) -
Keiko M. Aoki2008 年 77 巻 4 号 p. 044003
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありSymplectic integrators designed for simulating soft matter at constant temperature and constant pressure (or constant surface tension) are presented. In addition to the well-known merits of symplectic integrators, such as long time stability, these methods allow the estimation of thermal heat production/absorption and thus entropy differences through a simple function of the time scaling factor ν. The relative entropy estimation around crystal–liquid phase transition is given for systems with soft core repulsive potential.抄録全体を表示PDF形式でダウンロード (332K) -
Yasufumi Susuki, Yuugo Matsumoto, Taro Hosokawa, Yuuko Fukazawa2008 年 77 巻 4 号 p. 044301
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありAngle-dependent energy losses of well-collimated 5–10 keV protons scattered in collisions with CH4, C2H6, and C3H8 molecules have been measured. The thickness of the targets is less than 20 mPa·m, which is determined from the measured neutral fraction in the scattered beam and the charge-transfer cross sections reported by another group. The scattered protons have slightly expanded tails of the angular distribution. The measured energy losses increase with the angle. The stopping cross sections, which are obtained by integrating the angle-dependent energy losses over the square of the angle, agree well with the compilation values of SRIM-2006. The stopping cross sections are found to have a non-linear relationship with the size of target molecules. The contribution of a carbon atom attached by two hydrogen atoms of a heavier molecule becomes relatively small. This molecular size effect is enhanced with the decreasing energy of protons. Meanwhile, for protons that are deflected significantly, the molecular size effect is decreased.抄録全体を表示PDF形式でダウンロード (741K) -
Masayuki Sano, Mitsuaki Funakoshi2008 年 77 巻 4 号 p. 044401
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありThe instability of an axial uniform flow of a two-layer axisymmetric cylindrical sheet composed of two inviscid fluids is examined analytically and numerically on the basis of thin-layer approximation. As the eigenmodes for disturbances of large wavelength, we obtain an internal mode in which the displacement of interface between these fluids is larger than the displacements of two free surfaces of the sheet, as well as the modes similar to varicose and sinuous modes in a single-layer case. All the modes are unstable only for disturbances of large wavelength, and the growth rate of sinuous-like mode is much larger than that of two other modes. Furthermore, unlike a single-layer case, the wavenumber of disturbances of maximum growth rate is non-zero if the density ratio is sufficiently far from one. In such cases, the ratio of amplitudes of these disturbances is much different from that in a typical sinuous mode. The dependences of maximum growth rate on the ratios of surface tension coefficients, fluid densities, and sheet thicknesses are also examined.抄録全体を表示PDF形式でダウンロード (672K) -
Hidetsugu Sakaguchi, Kazutaka Noto2008 年 77 巻 4 号 p. 044402
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありWe investigate viscous fingers under the influence of surface tension anisotropy. Steady solutions in a channel are numerically solved using the Newton method. We study relations among the tip velocity v, the tip radius ρ and the pressure gradient Px. Power law relations are found in a parameter range, but the anisotropic viscous fingers do not always satisfy the relations such as vρ2=const. satisfied by dendrites in crystal growth.抄録全体を表示PDF形式でダウンロード (138K) -
Hiroshi Kuratsuji2008 年 77 巻 4 号 p. 044403
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありA field equation is studied for the light polarization in anisotropic media. The field of polarization is given by a spatial distribution of the Stokes vectors which is naturally deduced from the two-component Schrödinger type equation. The evolution equation is derived for the Stokes parameter (pseudo-spin) field by constructing the effective Lagrangian, which is similar to the equation of motion of texture in anisotropic fluid; superfluid He3 or liquid crystal. Some analytic solutions are obtained for a special case of nonlinear birefringent media for which the dielectric tensor is given by the Kerr effect.抄録全体を表示PDF形式でダウンロード (115K) -
Kazumasa Horigane, Hironori Nakao, Yusuke Kousaka, Tetsuya Murata, Yuk ...2008 年 77 巻 4 号 p. 044601
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありUsing neutron and resonant X-ray scattering, we studied crystal structure and charge-ordering pattern in La1.5Ca0.5CoO4. Taking A2mm with a–b type twin structure into account, Co2+/Co3+ checkerboard charge ordering pattern was suggested in La1.5Ca0.5CoO4 by neutron scattering structure analysis. In order to clarify the charge ordering pattern and the valences of the two Co sites, we performed a resonant X-ray scattering (RXS) measurement near the Co K-edge. We found a resonant signal at (3,0,0) reflection which corresponds to the charge ordering with a Co2+/Co3+ checkerboard pattern, and the Co valences of charge ordering were fully charge disproportionated. From the X-ray fluorescence spectra, we found the pre-edge peak structures at E=7.710 and 7.713 keV, corresponding to 1s→t2g and 1s→eg transitions, respectively. The polarization dependence of the latter one suggests that the anisotropy eg orbital is realized in La1.5Ca0.5CoO4.抄録全体を表示PDF形式でダウンロード (628K) -
Chiharu Mitsumata, Akimasa Sakuma, Kazuaki Fukamichi, Masakiyo Tsunoda ...2008 年 77 巻 4 号 p. 044602
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありThe exchange bias between the ferromagnetic (FM) and antiferromagnetic (AFM) bilayer was investigated within the framework of the classical Heisenberg model. The dependence of the exchange bias on the AFM layer thickness was also calculated by using the Landau–Lifshitz–Gilbert equation. The triple-Q (3Q), AF-I and T1 spin structures are obtained in the disordered γ-phase, ordered L10-, and L12-type lattices, respectively. The exchange bias is caused by the formation of the interfacial domain wall in the AFM layer, and the critical thickness dc of AFM layer is dominated by the varied spin structures. Under the condition where the magnetic anisotropy energy is fixed to equivalent values in different alloys, the critical thickness dc3Q of the disordered γ-phase layer with the 3Q spin structure is thinner than that dcAF-I of the ordered L10-type layer with the AF-I spin structure. Also, the critical thickness dcT1 is thinner than dcAF-I in ordered L12- and L10-type alloys. The relation among the critical thicknesses is dominated by the formation of a magnetic domain wall in the AFM layer. Consequently, the relation of the critical thickness can be represented as \\sqrt3dc3Q=\\sqrt2dcT1=dcAF-I.抄録全体を表示PDF形式でダウンロード (606K) -
Jian-Ming Lu, Yun-Che Wang, Jee-Gong Chang, Ming-Horng Su, Chi-Chuan H ...2008 年 77 巻 4 号 p. 044603
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありThis paper studies the buckling phenomena and mechanical behavior of single-walled carbon nanotubes (SWNTs) and double-walled carbon nanotubes (DWNTs) via molecular dynamics simulations. The Tersoff interatomic C–C potential is adopted. Using a dimensionless parameter, slenderness ratio (SR, the ratio of length to diameter), we investigate the mechanical behavior of long and short nanotubes under compression through their buckling modes, total strain energy and strain energy density, as well as post-buckling. The curvatures of strain energy provide a means to measure the Young’s modulus of the nanotubes. Moreover, jumps in either the strain energy or strain energy density indicate identical mechanical buckling strains, and are studied in relation to buckling modes. In our simulations, a transition time is observed for short nanotubes to reach stable vase-like buckling mode, indicating a time-dependent property of nanotubes. Furthermore, nanotubes with small SR can bear higher compressive load after their first buckling. In addition, nanotubes with same chirality exhibit roughly the same elastic modulus, regardless of their lengths, when applied compressive strains are less than 5% strain. However, long nanotubes show smaller buckling strength. Effects of temperature at 300 K on buckling strength for SWNT are also discussed in connection to our present study at 1 K.抄録全体を表示PDF形式でダウンロード (4056K) -
Osamu Kojima, Toshiro Isu, Junko Ishi-Hayase, Atsushi Kanno, Redouane ...2008 年 77 巻 4 号 p. 044701
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありWe report an ultrafast response of weakly confined excitons in GaAs thin films observed by a degenerate four-wave-mixing (DFWM) technique. The time-domain signals excited by broadband pulses show an oscillatory structure with a period that varies according to the pulse spectral width and an ultrafast response comparable to the pulse width; on the other hand, the exciton dephasing time is hardly changed by the excitation spectral width. This ultrafast response is much faster than the radiative lifetime expected on the basis of the nonlocal response theory. The DFWM spectra measured at various time delays clearly indicate the contribution of weakly confined excitons to the ultrafast response. Moreover, in the measurement of excitation-energy dependence, the time-domain signals excited by a controlled spectral width exhibit the variation of the oscillation period and response time. These characteristics are similar to those of the excitation spectral width dependence. From the analysis of oscillatory structures, it is found that the oscillation originates from the interference between weakly confined exciton states. Therefore, we conclude that the overlap of the oscillation due to the interference with the DFWM signal leads to the ultrafast response without any change in the exciton dephasing time. These results imply that the control of the excitation spectral width induces the ultrafast nonlinear optical response of the weakly confined excitons.抄録全体を表示PDF形式でダウンロード (180K) -
Shojiro Takeyama, Yoshiaki Natori, Yasuhiro Hirayama, Eiji Kojima, Yu ...2008 年 77 巻 4 号 p. 044702
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありWe have studied exciton complexes such as charged excitons and biexcitons in dilute magnetic semiconductor Cd1−xZnxTe/Cd1−x−yZnxMnyTe (x=0.07, y=0.43) quantum wells (well widths 4 and 9 nm). Laser excitation power dependence and time-resolved photoluminescence (PL) showed unique features related to excitons, charged excitons, and biexcitons. Four-wave-mixing spectroscopy with different choices of polarized incident light exhibited beating signals arising from exciton-biexciton interaction. Circular polarized PL was measured in magnetic fields of up to 42 T using a pulse magnet. The observed Zeeman splitting and the degree of circular polarization in magnetic fields revealed that the formation of biexcitons is quenched upon applying a magnetic field, and PL from the charged excitons was preserved up to the highest magnetic field.抄録全体を表示PDF形式でダウンロード (345K) -
Hidekatsu Suzuura, Tsuneya Ando2008 年 77 巻 4 号 p. 044703
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありZone-boundary phonons are described in a valence-force-field model and then converted into a continuum model. Only a mode with the highest frequency corresponding to a Kekulé-type distortion gives rise to inter-valley electron scattering between K and K′ points. An effective Hamiltonian for this interaction is obtained and used for the estimation of inter-valley scattering in graphene and nanotubes.抄録全体を表示PDF形式でダウンロード (249K) -
Lei Tan, Xiao-Fei Zang, Ju-Ping Li, Li-Wei Liu, Cai-Ying Ding, Qi-Rong ...2008 年 77 巻 4 号 p. 044704
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありThe dynamics of magnetization of a spin-1 Bose–Einstein condensate trapped in a double-well potential under external fields is investigated, focusing on the effects induced by the nonlinear self-interaction and the external magnetic field. Our numerical calculations show that the larger the external magnetic field is, the stronger the macroscopic quantum location of the condensate magnetization becomes.抄録全体を表示PDF形式でダウンロード (427K) -
Hideki Kumazaki, Dai S. Hirashima2008 年 77 巻 4 号 p. 044705
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありLocal magnetic moment formation on edges of graphene is studied using the Hubbard model on a honeycomb lattice. The Coulomb interaction is treated with the mean field approximation. Realistic edges of graphene are composed of zigzag and armchair parts. It is found that, on a zigzag part of length na larger than 3a, where a is the lattice constant, local staggered moment whose magnitude is proportional to the length of the zigzag part, is developed, i.e., a zigzag part of length 3a is sufficient for generation of local magnetism. This also means that one has to get rid of zigzag parts of n≥3 to suppress local edge magnetism of graphene.抄録全体を表示PDF形式でダウンロード (138K) -
Yugo Oshima, Hiroyuki Nojiri, Keisuke Fukaya, Toshihiro Yamase2008 年 77 巻 4 号 p. 044706
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありA high-field magnetization process for the triangular spin prism Na17[Mn6(H2O)2(AsW9O34)2(AsW6O26)]·38H2O, which consists of six Mn2+ ions (S=5⁄2), has been investigated. The magnetization at low temperature shows a 1/3 plateau around 5.5 T. It is examined by theoretical calculations using exact diagonalization. The experimental results can be reproduced, but only in a restricted parameter range. It implies that the plateau originates from a delicate balance of exchange couplings. We propose that the plateau is stabilized by some external perturbations, such as thermal/quantum fluctuations.抄録全体を表示PDF形式でダウンロード (722K) -
Kazuo Hida2008 年 77 巻 4 号 p. 044707
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありThe ground state phase diagram of the spin-1/2 Heisenberg frustrated Δ-chain with a ferromagnetic main chain is investigated. In addition to the ferromagnetic phase, various nonmagnetic ground states are found. If the ferromagnetic coupling between apical spins and the main chain is strong, this model is approximated by a spin-1 bilinear–biquadratic chain and the spin quadrupolar phase with spin-2 gapless excitation is realized in addition to the Haldane and ferromagnetic phases. In the regime where the coupling between the apical spins and the main chain is weak, the numerical results which suggest the possibility of a series of phase transitions among different nonmagnetic phases are obtained. Physical pictures of these phases are discussed based on the numerical results.抄録全体を表示PDF形式でダウンロード (271K) -
Kensuke Fujii, Yoshinori Ohmasa, Shin Takahashi, Takuya Katayama, Wata ...2008 年 77 巻 4 号 p. 044708
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありComplex dielectric function for liquid Se–Tl mixtures has been obtained by ellipsometric measurements at temperatures between 300 and 500 °C. The optical gap decreases rapidly with increasing Tl-concentration in the low concentration region less than 15 at. % Tl, while it remains nearly constant for higher concentrations up to 40 at. % Tl. A long-standing problem of the discrepancy between the activation energies of the electrical conductivity and thermopower can be resolved by considering the temperature dependence of the energy gap precisely.抄録全体を表示PDF形式でダウンロード (246K) -
Daisuke Okuyama, Takeshi Matsumura, Takuya Mouri, Naoko Ishikawa, Kenj ...2008 年 77 巻 4 号 p. 044709
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありThe successive magnetic phase transitions of HoB4 with TN1=7.1 K and TN2=5.7 K have been investigated in detail by neutron and X-ray diffraction. Since Ho ions in the c-plane form a Shastry–Sutherland lattice, geometrical frustration has been expected in this compound. Below TN1, HoB4 exhibits an incommensurate antiferromagnetic order with q=(δ,δ,δ′) (δ=0.022, δ′=0.43), followed by a first-order transition at TN2 into a commensurate order with q=(0,0,0), where four magnetic moments are antiferromagnetically coupled in a unit cell. After determining the magnetic structures of the two phases by neutron powder diffraction, we pay particular attention to diffuse scatterings responsible for the critical behavior. Very broad diffuse scatterings, extending almost to the zone boundary, are observed already in the paramagnetic phase at around q=(0,0,0) and (0,0,1⁄2) with magnetic correlation lengths of ξ<10 Å. Below TN1, a strong diffuse scattering develops in a more concentrated region at around q=(0,0,δ′) with ξ∼30 Å, followed by the appearance of a Bragg peak at (δ,δ,δ′). Simultaneously, a sharp Bragg peak corresponding to q=(0,0,0) also develops at (1,0,1) upon diffuse scattering. This complex critical behavior is discussed from the viewpoint of competing order parameters of magnetic and quadrupolar origins. The striking resemblance of the critical behavior to that of HoB2C2 with a square lattice of Ho is interpreted as a manifestation of a universality for a three-dimensional system with competing magnetic and quadrupolar order parameters and a long-ranged RKKY interaction. It is considered that the microscopic difference in interionic interaction due to the difference in crystal structure becomes less prominent in the critical behavior as the correlation length becomes much larger than the lattice constant. On the other hand, the strong diffuse scattering in HoB4, which is hardly detected in HoB2C2, might be ascribed to geometrical frustration. The softening of the elastic constant in HoB4 and HoB2C2 is also discussed.抄録全体を表示PDF形式でダウンロード (1737K) -
Gaku Motoyama, Katsuhiro Maeda, Yasukage Oda2008 年 77 巻 4 号 p. 044710
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありMeasurements of specific heat between 80 mK to 4 K and electrical resistivity between 80 mK to 10 K were carried out for polycrystalline CePt3Si samples cut into small pieces (typically ∼10 mg). In the specific heat measurements, we observed an antiferromagnetic transition jump at TN=2.2 K for all the samples, while the heights have large variations. As regards superconductivity, we observed two distinct transition jumps at Tcl∼0.45 K and Tch∼0.75 K, which were the same for all the samples. From the measurements of specific heat and resistivity, systematic relations were found between antiferromagnetic and superconducting transitions. We conclude that antiferromagnetism, whose transition temperature is 2.2 K, coexists with superconductivity, whose transition temperature is Tcl. In this sample, residual electronic specific heat coefficient in the superconducting state γs was quite small, and specific heat divided by temperature below Tcl decreased almost linearly with decreasing temperature. In order to reveal the characteristic properties of the magnetism and superconductivity of the CePt3Si system, it is important to study the two superconducting phases with Tcl and Tch, respectively.抄録全体を表示PDF形式でダウンロード (324K) -
Toshiki Yamaji, Miwa Murakami, Jun Fukazawa, Tadashi Shimizu, Kiyonori ...2008 年 77 巻 4 号 p. 044711
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証あり11B nuclear magnetic resonance (NMR) measurements have been performed on MgB2 powder sample at several magnetic fields ranging from 6.3 to 21.9 T. The isotropic Knight-shift, as well as quadrupole coupling frequency, was accurately determined from magic-angle spinning (MAS) spectra by analyzing its magnetic-field dependence. These NMR parameters were then used to interpret its static powder-pattern spectra observed at various magnetic fields, which reflect both the anisotropic Knight-shift tensor and the second-order quadrupole coupling tensor. We found that the Knight-shift tensor and the quadrupole coupling are both axially symmetric and their relative orientation to the molecular frame was also determined. This is the first experimental determination of the anisotropy of the Knight-shift of MgB2 in a powder form from an exact analysis of the powder lineshape of the 11B NMR spectra. The anisotropy was found to be very small (∼4 ppm), being in consistent with previous observations indicating that anisotropy of electronic conductivity in MgB2 is small.抄録全体を表示PDF形式でダウンロード (361K) -
Ni Ni Soe, Masahiro Nakagawa2008 年 77 巻 4 号 p. 044801
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありThis paper presents the novel approach to evaluate the effects of different motor activation tasks of the human electroencephalogram (EEG). The applications of chaos and fractal properties that are the most important tools in nonlinear analysis are been presented for four tasks of EEG during the real and imaginary motor movement. Three subjects, aged 23–30 years, participated in the experiment. Correlation dimension (D2), Lyapunov spectrum (λi), and Lyapunov dimension (DL) are been estimated to characterize the movement related EEG signals. Experimental results show that these nonlinear measures are good discriminators of EEG signals. There are significant differences in all conditions of subjective task. The fractal dimension appeared to be higher in movement conditions compared to the baseline condition. It is concluded that chaos and fractal analysis could be powerful methods in investigating brain activities during motor movements.抄録全体を表示PDF形式でダウンロード (2909K) -
Atsumasa Hojo, Hiroshi Matsui, Kei Iwamoto, Takeshi Yanagimachi, Hasan ...2008 年 77 巻 4 号 p. 044802
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありUsing a microwave cavity-perturbation method, the temperature dependence of the complex dielectric constant (\\ ildeε=ε1+iε2) at 16.3 GHz is measured on a dry poly(dA)–poly(dT) DNA sample prepared under three-different relative humidity (RH) of 0, 11 and 93%. For RH=0%, the temperature dependence of both ε1 and ε2 are explained by the rotational motion of water molecules electrostatically bonding to the negatively charged phosphate group in the primary hydration shell. The activation-type behavior in ε2 is discussed with a double-well potential for a process that the electric dipole of the hydrated water is thermally rotated to the adjacent phosphate groups. For RH=11%, ε2 takes a broad maximum at 280 K due to the collective motion of water molecules in the primary hydration shell. While these features qualitatively resemble to those of free water, the absolute values are much small due to an extremely small number of hydrated water molecules. Moreover the conformation is expected to be of A form, in which the hydration bridge could be constructed in the major groove via hydrogen bonds as suggested by previous X-ray and neutron diffraction experiments. For RH=93%, in addition to the collective motion of the primary hydration shell, a freezing process of the secondary hydration shell appears. Independently on RH, the hydrated water molecules at low temperatures around 200 K or below are hard to respond to microwave electric fields, and hence both the rotational and collective motions cannot be permitted. Approaching to 420 K, ε2 becomes suppressed converging to the same value. The suppression comes from a thermally induced dehydration resulting in eventual reduction of the hydration density down to 0.1 water molecules per nucleotide as revealed by our previous infrared spectroscopy.抄録全体を表示PDF形式でダウンロード (384K) -
Hong-Hai Hao, Da-Jun Zhang2008 年 77 巻 4 号 p. 045001
発行日: 2008/04/15
公開日: 2011/12/28
ジャーナル 認証ありPDF形式でダウンロード (103K)
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