著者

Kim Kang Miyazaki Kunimasa Saito Shinji

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.23, no.23, pp.234123, 2011-05

被引用文献数

40 26

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Using molecular dynamics simulations, we study the slow dynamics of supercooled liquidsconfined in a random matrix of immobile obstacles. We study the dynamical crossover fromglass-like to Lorentz-gas-like behavior in terms of the density correlation function, the meansquare displacement, the nonlinear dynamic susceptibility, the non-Gaussian parameter, and thefragility. We find the cooperative and spatially heterogeneous dynamics to be suppressed as theobstacle density increases, leading to a more Arrhenius-like behavior in the temperaturedependence of the relaxation time. Our findings are qualitatively consistent with the results ofrecent experimental and numerical studies for various classes of spatially heterogeneoussystems. We also investigate the dependence of the dynamics of mobile particles on theprotocol used to generate the random matrix. A re-entrant transition from the arrested phase tothe liquid phase as the mobile particle density increases is observed for a class of protocols.This re-entrance is explained in terms of the distribution of the volume of the voids that areavailable to the mobile particles.

著者

Hishida M Tanaka K

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.24, no.28, pp.284113, 2012-07

被引用文献数

22

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What role does water play in the self-assembly of soft materials? To understand the correlation between the hydration state and the various self-assembled structures of a nonionic surfactant, terahertz time-domain spectroscopy has been performed for a C(12)E(5) solution with complementary use of small-angle x-ray scattering. Precise observations of the hydration state show clearly that transitions of the hydration state are accompanied by structural phase transitions of the surfactant from hexagonal to micelle to lamellae. These transitions of hydration state suggest that water is not a homogeneous solvent, and the interaction between water and the soft material is important for self-assembly.

著者

Klemm Richard A Kadowaki Kazuo

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.22, no.37, pp.375701, 2010-08

被引用文献数

74 36

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The angular dependence of the radiation-zone output power and electric polarization of stimulated terahertz amplified radiation (STAR) emitted from a dc voltage applied across cylindrical and rectangular stacks of intrinsic Josephson junctions is calculated. The boundary conditions are obtained from Love's equivalence principles. During coherent emission, a spatially uniform ac Josephson current density in the stack acts as a surface electric current density antenna source, leading to a harmonic radiation frequency spectrum, as in experiment, but absent in all cavity models of cylindrical mesas. Spatial fluctuations of the ac Josephson current allow its fundamental mode to lock onto the lowest finite energy cylindrical cavity mode, causing it to resonate, leading to a non-uniform magnetic surface current density radiation source, and a non-trivial combined fundamental frequency output power with linear polarization for general radiation directions, which may be fully or partially coherent. The higher ac Josephson harmonics do not excite other cylindrical cavity modes. For rectangular mesas, the lowest energy modes are empirically not excited, but the non-uniform ac Josephson current can excite the harmonic sequence of modes with spatial variation across the rectangular widths, leading to combined radiation outputs both for the fundamental and the higher harmonics, which combinations also may be either fully or partially coherent. The superconducting substrate is modeled as a perfect magnetic conductor, greatly reducing the STAR emitter power and modifying its angular dependence, especially parallel to the substrate. Based upon this substrate model, existing Bi2Sr2CaCu2O8 + δ crystals atop perfect electric conductors could have STAR emitter power in excess of 5 mW, acceptable for many device applications.

著者

Oh Junepyo Kondo Takahiro Hatake Daigo Honma Yujiro Arakawa Keitaro Machida Takahiro Nakamura Junji

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.22, no.30, pp.304008, 2010-07-13

被引用文献数

8 6

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The effect of the local electronic modification of the graphite surface on the gas–graphite interaction has been investigated by the molecular beam scattering technique. The angular intensity distributions of He and Ar beams scattered from pristine and defect induced graphite surfaces have been measured at various surface temperatures. From the He scattering results, the cross-section for the He diffuse scattering per defect is estimated as being as much as 113 nm2. The origin of the extremely large cross-section is ascribed to the modulated electronic states of graphite around the defect based on the STM measurements, which is due to the local breaking of the π conjugated system of graphite. From the Ar scattering results, the effective mass of the graphite surface for the Ar collision has been estimated as M = 114 u, based on the analysis with the hard cube model. The new component appears in the scattering distribution of Ar for the defect induced graphite surface. The component has a larger peak position angle than that for the pristine graphite surface, indicating that the normal component of the translational energy of the Ar atom was greatly lost by the collision at the electronically modified area of graphite.

著者

Terada Yasuhiko Yoshida Shoji Takeuchi Osamu Shigekawa Hidemi

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.22, no.26, pp.264008, 2010-07

被引用文献数

32 25

---

The development of time-resolved scanning tunnelling microscopy (STM), in particular, attempts to combine STM with ultrafast laser technology, is reviewed with emphasis on observed physical quantities and spatiotemporal resolution. Ultrashort optical pulse technology has allowed us to observe transient phenomena in the femtosecond range, which, however, has the drawback of a relatively low spatial resolution due to the electromagnetic wavelength used. In contrast, STM and its related techniques, although the time resolution is limited by the circuit bandwidth (~100 kHz), enable us to observe structures at the atomic level in real space. Our purpose has been to combine these two techniques to achieve a new technology that satisfies the requirements for exploring the ultrafast transient dynamics of the local quantum functions in organized small structures, which will advance the pursuit of future nanoscale scientific research in terms of the ultimate temporal and spatial resolutions.

著者

Hagiwara Yohsuke Tateno Masaru

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.21, no.24, pp.245103, 2009-05

被引用文献数

3 2

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Stacking involving aromatic rings has a significant contribution to the structural stability of biological macromolecules. However, conventional calculations such as density functional theory (DFT) and molecular mechanics (MM) fail to estimate such stabilization energies, most of which are fundamentally derived from van der Waals interactions. For the accurate description, higher level ab initio calculations, such as CCSD(T), should be employed; however, their computational costs are huge. MM calculations provide better estimation of the interactions of the aromatic rings than DFT, but not sufficient. In this report, we propose a novel scheme to calculate the interaction energy at an accuracy compatible to CCSD(T) with the computational costs comparable to MM calculations. In our scheme, the electron density of the aromatic rings is represented by Gaussian-type functions, and the parameters involved in the functions are determined by an optimization scheme to reproduce the CCSD(T) results. Here, we employ model structures involving tryptophan and tyrosine rings, and successfully obtain the optimal parameter set. By using this type of representation of the stacking proposed, the computational time to calculate the interaction energy is dramatically reduced by 10−10-fold, compared with CCSD(T).

著者

Lushnikov S G Fedoseev A I Gvasaliya S N Ko J-H Kojima Seiji

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.19, no.49, pp.496206, 2007-11

被引用文献数

7 6

---

The behavior of longitudinal acoustic (LA) and transverse acoustic (TA) phonons in a cubic relaxor PbMg1/3Ta2/3O3 (PMT) ferroelectric has been investigated by Brillouin light scattering. Analysis of the temperature dependences of phonon velocity in the temperature range from 50 to 870 K has revealed anomalies in the vicinity of the Burns temperature (TB≈570 K) for LA phonons and a wide frequency-dependent minimum of the velocities of LA and TA phonons in the same temperature region as the dielectric response anomaly. Using experimental data, temperature dependences of the C11 and C44 elastic constants have been calculated. The elastic constants have been found to be frequency-independent in the gigahertz range. The results obtained are discussed in the framework of modern ideas on the crystalline lattice dynamics of relaxor ferroelectrics.

著者

Okada Susumu Nakada Kyoko Kawai Takazumi

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.19, no.36, pp.365231, 2007-09

被引用文献数

1

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We study the electronic structure and energetics of carbon nanotubes with topological line defects consisting of fused pentagons and octagon rings by means of first-principles calculation in density functional theory and tight-binding molecular dynamics simulations. The tubes with the topological line defects are found to exhibit magnetic ordering where polarized electron spins are localized around the topological defect and ferromagnetically aligned along the defect. Our analyses of the electronic energy band and spin density distributions reveal that this ferromagnetic spin ordering is associated with the edge states that are inherent in the graphite ribbon with zigzag edges. The tight-binding molecular dynamics simulations show that the nanotubes with the topological line defects are thermally stable up to temperature of 3000 K and disrupted over 4000 K.

著者

Onoda Masashige Kikuchi Yuji

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.19, no.34, pp.346206, 2007-08

被引用文献数

5

---

A new type of the triangular lattice system HxCoO2 (x ≈ 0.3)is synthesized through a chemical extraction of Na from Na0.3CoO2 withH2SO4. The structure is modelled by two oxygen layers with a prismaticoxygen environment and a symmetric linear H−O bond on the basis of the xraypowder diffraction and magic-angle spinning NMR analyses. Measurementsof the electrical resistivity, thermoelectric power and magnetic susceptibilitysuggest a weakly correlated metallic state with the enhancement of effective mass.The transport anomalies, accompanied with the rapid decrease of thermoelectricpower, are observed at about 10 K.

著者

Hatsugai Yasuhiro

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.19, pp.145209, 2007-04

被引用文献数

32 13

---

Recently, by using quantized Berry phases, a prescription for a local characterization of gapped topological insulators has been given (Hatsugai 2006 Preprint cond-mat/0603230). It requires that the ground state is gapped and is invariant under some anti-unitary operation. A spin liquid which is realized as a unique ground state of the Heisenberg spin system with frustrations is a typical target system, since pairwise exchange couplings are always time-reversal invariants even with frustrations.As for a generic Heisenberg model with a finite excitation gap, we locally modify the Hamiltonian by a continuous SU(2) twist only at a specific link and define the Berry connection by the derivative. Then the Berry phase evaluated by the entire many-spin wavefunction is used to define the local topological order parameter at the link. We numerically apply this scheme for several spin liquids and show its physical validity. For example, it implies that the Haldane phase of the S = 1 chains is characterized by uniform π quantized Berry phases.