Experimental and Theoretical Investigations of the Negative Differential Resistance in a Discharge Plasma

Maricel Agop, Petru Nica, Oana Niculescu, and Dan-Gheorghe Dimitriu — 2012-05-11T09:00:00+09:00

Authors: Maricel Agop, Petru Nica, Oana Niculescu, and Dan-Gheorghe Dimitriu
Negative differential resistance effect in the current–voltage characteristic simultaneously with the generation of a fireball in a plasma diode was experimentally evidenced by increasing the voltage applied on a supplementary electrode immersed into plasma. This effect is associated with a bistabilitiy in the frame of a hydrodynamic model by assuming that the electronic component of plasma is non-inertial (while the ionic one is inertial) and that the movements of electrons take place on continuous but non-differentiable curves, i.e., fractal curves.©2012 The Physical Society of Japan

Writing Nanowires with Large Conductivity Ratios in LaAlO_{3}/SrTiO_{3} Interfaces

2012-05-11T09:00:00+09:00

Authors: Cyril Stephanos, Martin Breitschaft, Rainer Jany, Birgit Kiessig, Stefan Paetel, Christoph Richter, and Jochen Mannhart
Using a charged AFM tip allows nanometer-wide conducting lines to be written into otherwise insulating LaAlO_{3}/SrTiO_{3} interfaces. Based on studies and modifications of this process, this report describes the writing and erasing of such nanowires with conductivity changes by factors of more than 10^{7}, which far exceeds previously reported values. The lines are found to have lifetimes of several days.©2012 The Physical Society of Japan

Superconductivity in Pt Doped BaFe_{2}As_{2}

2012-05-11T09:00:00+09:00

Authors: Yanfeng Guo, Xia Wang, Jun Li, Shoubao Zhang, Kazunari Yamaura, and Eiji Takayama-Muromachi
A high-pressure method was used to systematically dope an antiferromagnetically metallic compound, BaFe_{2}As_{2}, with Pt, and the doped compounds were studied using X-ray diffraction, energy dispersive X-ray spectroscopy, and by measuring the electrical resistivity, magnetic susceptibility, and specific heat. This method significantly increased the Pt doping level for BaFe_{2}As_{2}, resulting in a revision of the phase diagram proposed for BaFe_{2-x}Pt_{x}As_{2}. The Pt doped system showed a dome-like superconductivity region in the thermal phase diagram (0.02< x< 0.20) with an optimal T_{c} of 24.2 K (x = 0.08), instead of the unusually wide superconductivity region found in early studies. Further doping beyond the optimal Pt concentration led to T_{c} continuously decreasing toward zero. The common superconducting feature of the 3d and 4d doped systems, BaFe_{2-x}M_{x}As_{2} (M = Co, Ni, Rh, or Pd), was confirmed for the 5d doped system, BaFe_{2-x}Pt_{x}As_{2}, which suggested that the electron–phonon coupling was insignificant at the superconducting state.©2012 The Physical Society of Japan

Quantum Hall Effects in Silicene

Motohiko Ezawa — 2012-05-11T09:00:00+09:00

Authors: Motohiko Ezawa
We investigate quantum Hall effects in silicene by applying electric field E_{z} parallel to magnetic field. Silicene is a monolayer of silicon atoms forming a two-dimensional honeycomb lattice, and shares almost every remarkable property with graphene. A new feature is its buckled structure, due to which the band structure can be controlled externally by changing E_{z}. The low energy physics of silicene is described by massive Dirac fermions, where the mass is a function of E_{z} and becomes zero at the critical field E_{cr}. We show that there are no zero energy states due to the Dirac mass term except at the critical electric field E_{cr}. Furthermore it is shown that the 4-fold degenerate zero-energy states are completely resolved even without considering Coulomb interactions. These features are highly contrasted with those in graphene, demonstrating that silicene has a richer structure. The prominent feature is that, by applying the electric field, we can control the valley degeneracy. As a function of E_{z}, Hall plateaux appear at the filling factors ν= 0, ±1, ±2, ±3, ... except for the points where level crossings occur.©2012 The Physical Society of Japan

Formation of Step Bunches Induced by Flow in Solution

Masashi Inaba and Masahide Sato — 2012-05-10T09:00:00+09:00

Authors: Masashi Inaba and Masahide Sato
We study the formation of step bunches induced by flow in solution during growth. In our previous study [M. Inaba and M. Sato: J. Phys. Soc. Jpn. 80 (2011) 074606], we showed that the step-down flow in solution causes bunching. In this research, we study the dependence of step behavior on some parameters. With a slow flow, the separation and coalescence between steps and bunches occur frequently during step bunching. With increasing flow rate, the frequency decreases and tight bunches are formed. The decrease in the frequency also occurs with increasing strength of the repulsion between steps.©2012 The Physical Society of Japan

Magnetic Structure of SrCo_{3}P_{4}O_{14} Determined from Neutron Powder Diffraction Results

Masashi Hase, Vladimir Yu. Pomjakushin, Andreas Dönni, and Hideaki Kitazawa — 2012-05-10T09:00:00+09:00

Authors: Masashi Hase, Vladimir Yu. Pomjakushin, Andreas Dönni, and Hideaki Kitazawa
The spin system in SrCo_{3}P_{4}O_{14} was reported to be a J_{1}–J_{1}–J_{2} trimerized spin-3/2 chain. The J_{1} and J_{2} exchange interactions were antiferromagnetic and ferromagnetic, respectively. However, in spite of expectation for the trimerized spin chain, a 1/3 quantum magnetization plateau does not appear. To investigate the sign of exchange interactions, we determined the magnetic structure using neutron powder diffraction measurements. Both the J_{1} and J_{2} exchange interactions are ferromagnetic. The previously reported spin system is incorrect. Therefore, no 1/3 quantum magnetization plateau exists.©2012 The Physical Society of Japan

Field-Induced Magnetostructural Transitions in Antiferromagnetic Fe_{1+y}Te_{1-x}S_{x}

Masashi Tokunaga, Takumi Kihara, Yoshikazu Mizuguchi, and Yoshihiko Takano — 2012-05-07T09:00:00+09:00

Authors: Masashi Tokunaga, Takumi Kihara, Yoshikazu Mizuguchi, and Yoshihiko Takano
The transport and structural properties of Fe_{1+y}Te_{1-x}S_{x} (x=0, 0.05, and 0.10) crystals were studied in pulsed magnetic fields up to 65 T. The application of high magnetic fields resulted in a positive magnetoresistance effect with prominent hysteresis in the antiferromagnetic state. Polarizing microscope images obtained at high magnetic fields showed simultaneous occurrences of structural transitions. These results indicate that magnetoelastic coupling is the origin of the bicollinear magnetic order in iron chalcogenides.©2012 The Physical Society of Japan

Analysis of XY Model with Mexican-Hat Interaction on a Circle –Derivation of Saddle Point Equations and Study of Bifurcation Structure–

Tatsuya Uezu, Tomoyuki Kimoto, and Masato Okada — 2012-05-07T09:00:00+09:00

Authors: Tatsuya Uezu, Tomoyuki Kimoto, and Masato Okada
In our previous study, we investigated a classical XY model on a circle by adopting the Mexican-hat type interaction, which is composed of uniform and location-dependent interactions. We solved the saddle point equations numerically and found three non-trivial solutions. In this study, we determined the phases of complex order parameters and derived the saddle point equations for stable and unstable nontrivial solutions and the formula of boundaries of bistable regions analytically. We performed Markov Chain Monte Carlo simulations and confirmed that the numerical and theoretical results agree well.©2012 The Physical Society of Japan

Low-Temperature Properties of the Fermionic Mixtures with Mass Imbalance in Optical Lattice

Nayuta Takemori and Akihisa Koga — 2012-05-02T09:00:00+09:00

Authors: Nayuta Takemori and Akihisa Koga
We study the attractive Hubbard model with mass imbalance to clarify the low-temperature properties of fermionic mixtures in an optical lattice. By combining dynamical mean-field theory with continuous-time quantum Monte Carlo simulation, we discuss the competition between the superfluid and density wave states at half filling. By calculating the energy and order parameter for each state, we clarify that the coexisting (supersolid) state, where the density wave and superfluid states are degenerate, is realized in the system. We then determine the phase diagram at finite temperatures.©2012 The Physical Society of Japan

Transformation of the Transverse Beam Intensity Distribution by Sextupole Focusing in a Transport Line

2012-05-02T09:00:00+09:00

Authors: Yosuke Yuri, Takahiro Yuyama, Tomohisa Ishizaka, Ikuo Ishibori, and Susumu Okumura
We investigate the transformation of the transverse intensity distribution of a charged-particle beam focused by one or two sextupole magnets in a beam transport line. It is expected, from the equation of transverse motion, that the beam is deflected toward one direction and thus deformed due to the second-order force of the sextupole magnet. Such a sextupole-induced deformation of the beam distribution has been studied analytically in detail. The beam centroid displacement and the change of the beam size are determined using the first-order and second-order moments of the intensity distribution function. In order to verify the theoretical consideration, numerical simulations and experiments were performed at the cyclotron facility of Japan Atomic Energy Agency. We experimentally demonstrate that an ion beam with a uniform transverse distribution can be formed using two sextupole magnets.©2012 The Physical Society of Japan

Low-Energy Effective Hamiltonian and the Surface States of Ca_{3}PbO

Toshikaze Kariyado and Masao Ogata — 2012-05-02T09:00:00+09:00

Authors: Toshikaze Kariyado and Masao Ogata
The band structure of Ca_{3}PbO, which possesses a three-dimensional massive Dirac electron at the Fermi energy, is investigated in detail. Analysis of the orbital weight distributions on the bands obtained in the first-principles calculation reveals that the bands crossing the Fermi energy originate from the three Pb-p orbitals and three Ca-d_{x^{2}-y^{2}} orbitals. Taking these Pb-p and Ca-d_{x^{2}-y^{2}} orbitals as basis wave functions, a tight-binding model is constructed. With the appropriate choice of hopping integrals and the strength of the spin–orbit coupling, the constructed model successfully captures important features of the band structure around the Fermi energy obtained in the first-principles calculation. By applying a suitable basis transformation and expanding the matrix elements in the series of the momentum measured from a Dirac point, the low-energy effective Hamiltonian of this model is explicitly derived and proved to be a Dirac Hamiltonian. The origin of the mass term is also discussed. It is shown that the spin–orbit coupling and orbitals other than Pb-p and Ca-d_{x^{2}-y^{2}} orbitals play important roles in making the mass term finite. Finally, the surface band structures of Ca_{3}PbO for several types of surfaces are investigated using the constructed tight-binding model. We find that there appear nontrivial surface states that cannot be explained as bulk bands projected onto the surface Brillouin zone. The relation between Ca_{3}PbO and a topological insulator is also discussed.©2012 The Physical Society of Japan

Mott Transition and Spin Structures of Spin-1 Bosons in Two-Dimensional Optical Lattice at Unit Filling

2012-05-01T09:00:00+09:00

Authors: Yuta Toga, Hiroki Tsuchiura, Makoto Yamashita, Kensuke Inaba, and Hisatoshi Yokoyama
We study the ground state properties of spin-1 bosons in a two-dimensional optical lattice by applying a variational Monte Carlo method to the S=1 Bose–Hubbard model on a square lattice at unit filling. A doublon–holon binding factor introduced in the trial state provides a noticeable improvement in the variational energy over the conventional Gutzwiller wave function and allows us to effectively deal with the intersite correlations of particle densities and spins. We systematically show how spin-dependent interactions modify the superfluid-Mott insulator transitions in the S=1 Bose–Hubbard model owing to the interplay between the density and spin fluctuations of bosons. Furthermore, regarding the magnetic phases in the Mott region, the calculated spin structure factor elucidates the emergence of nematic and ferromagnetic spin orders for antiferromagnetic (U_{2}>0) and ferromagnetic (U_{2}<0) couplings, respectively.©2012 The Physical Society of Japan

Quantum Limiting Behaviors of a Vortex Core in an Anisotropic Gap Superconductor

2012-05-01T09:00:00+09:00

Authors: Shin-ichi Kaneko, Ken Matsuba, Muhammad Hafiz, Keigo Yamasaki, Erika Kakizaki, Nobuhiko Nishida, Hiroyuki Takeya, Kazuto Hirata, Takuto Kawakami, Takeshi Mizushima, and Kazushige Machida
Quantized bound states at a vortex core are discretized in YNi_{2}B_{2}C. By using scanning tunneling spectroscopy with an unprecedented 0.1 nm spatial resolution, we find and identify the localized spectral structure, where in addition to the first main peak with a positive low energy, a second subpeak coming from the fourfold symmetric gap structure is seen inside the energy gap. Those spectral features are understood solving the Bogoliubov–de Gennes equation for a fully three-dimensional gap structure. A particle–hole asymmetric spectrum at the core site and quantum oscillation in the spectra are clearly observed.©2012 The Physical Society of Japan

Study of Neutron Diffraction on ^{154}SmRu_{4}P_{12} Single Crystal

2012-05-01T09:00:00+09:00

Authors: Chul-Ho Lee, Satoshi Tsutsui, Kunihiro Kihou, Hitoshi Sugawara, and Hideki Yoshizawa
The magnetic structure of SmRu_{4}P_{12} has been investigated by neutron diffraction. Long-range antiferromagnetic ordering with a propagating vector of q=(1,0,0) was observed below the metal–insulator transition temperature (T_{MI}=16.5 K). Data obtained at T=3.3 K were analyzed with dipole magnetic moments of µ=0.30 µ_{B} at Sm sites. The results suggest that the primary order parameter is the T^{α}, or T^{β} octupole accompanied by strong mixing with T^{α} and dipoles.©2012 The Physical Society of Japan

Explicit Expression for Steady Plane Irrotational Incompressible Flow around Obstacles

Kurt Fischer — 2012-04-27T09:00:00+09:00

Authors: Kurt Fischer
We obtain the steady plane irrotational incompressible flow around an arbitrary obstacle, using the inverse Koebe algorithm to construct the Laurent series of the conformal map of the exterior of the unit disk onto the exterior of the obstacle. We provide a list of Laurent polynomials for various obstacles as well as the source code in Octave. We also estimate the accuracy of the inverse Koebe algorithm and its Laurent polynomial approximation.©2012 The Physical Society of Japan

Spin and Chiral Orderings of the Antiferromagnetic XY Model on the Triangular Lattice and Their Critical Properties

Tomoyuki Obuchi and Hikaru Kawamura — 2012-04-27T09:00:00+09:00

Authors: Tomoyuki Obuchi and Hikaru Kawamura
We study the antiferromagnetic XY model on a triangular lattice by extensive Monte Carlo simulations, focusing on its ordering and critical properties. Our result clearly shows that two separate transitions occur at two distinct temperatures, the one at a higher temperature is associated with a Z_{2}-symmetry breaking driven by the chirality, and the one at a lower temperature is associated with the onset of the quasi-long-range order of the XY spin. We carefully examine the critical properties of each transition to find that the criticality of the chiral transition is consistent with the standard two-dimensional Ising universality class, whereas that of the spin transition might differ from the conventional Kosterlitz–Thouless (KT) one. The observed non-KT nature of the spin criticality is consistent with the most recent simulation result on the fully-frustrated XY model on a square lattice.©2012 The Physical Society of Japan

Comment on “Details of Sample Dependence and Transport Properties of URu_{2}Si_{2}”

Nicholas P. Butch, Jason R. Jeffries, and M. Brian Maple — 2012-04-26T09:00:00+09:00

Authors: Nicholas P. Butch, Jason R. Jeffries, and M. Brian Maple

Reply to “Comment on `Details of Sample Dependence and Transport Properties of URu_{2}Si_{2}”'

Tatsuma D. Matsuda, Dai Aoki, Georg Knebel, Yoshinori Haga, and Jacques Flouquet — 2012-04-26T09:00:00+09:00

Authors: Tatsuma D. Matsuda, Dai Aoki, Georg Knebel, Yoshinori Haga, and Jacques Flouquet

Analysis of C V Ions by Measuring Line Ratios in the LHD

2012-04-25T09:00:00+09:00

Authors: Mi-Young Song, Izumi Murakami, Takako Kato, Chihiro Suzuki, Hiroyuki A. Sakaue, and Shigeru Morita
We measured time-dependent extreme ultraviolet spectra to carry out a quantitative study of impurity spectral lines of C V in the Large Helical Device (LHD) at the National Institute for Fusion Science. In order to analyze these C V spectra, we calculated the intensity ratios of spectral lines of C V using our collisional-radiative model and compared the results to observed time-dependent intensity ratios. We derived the electron temperature from the measured intensity ratio and estimated the location of the C V emitting region by comparing the derived temperature with the electron temperature distribution measured by the Thomson scattering. Through the C V emitting region, we see that the C V appears just after carbon pellet ablation caused by the bulk plasma at 2.8 s and moves toward the wall until ∼3.0 s.©2012 The Physical Society of Japan

Observation of Structural Change in the Novel Ferromagnetic Metal–Insulator Transition of K_{2}Cr_{8}O_{16}

2012-04-25T09:00:00+09:00

Authors: Akiko Nakao, Yuki Yamaki, Hironori Nakao, Youichi Murakami, Kunihiro Hasegawa, Masahiko Isobe, and Yutaka Ueda
The synchrotron X-ray diffraction analysis of a single crystal of K_{2}Cr_{8}O_{16} has revealed a change from a tetragonal I4/m structure to a monoclinic P112_{1}/a (or P112_{1}/b) structure across the metal–insulator transition at 95 K. In the low-temperature ferromagnetic insulator phase, almost the same Cr–O bond lengths for the four Cr sites indicate no charge separation/order. However, characteristic displacements of the Cr and O sites, resulting in Cr–O bond alternations, are observed in a rectangular column formed by four CrO_{6} chains (four-chain column), which indicates the dimerization of the lattice with the formation of a Cr tetramer. There are two means of lattice dimerization. The spatial arrangement of the two types of four-chain columns with lattice dimerization is of neither the uniform type nor the checkerboard type but is of the stripe type. Such a stripe-type arrangement would result from the competition between lattice distortion and coulomb repulsion.©2012 The Physical Society of Japan

Absence of Quantum Criticality and Presence of Superconducting Fluctuation in Pressure-Induced Heavy-Fermion Superconductor CeRhSi_{3}

Tetsuya Sugawara, Hiroki Iida, Haruyoshi Aoki, and Noriaki Kimura — 2012-04-25T09:00:00+09:00

Authors: Tetsuya Sugawara, Hiroki Iida, Haruyoshi Aoki, and Noriaki Kimura
We report the pressure dependence of antiferromagnetism and superconductivity in the heavy-fermion CeRhSi_{3} on the magnetic field in the tetragonal basal plane. The anomaly of the resistivity at the antiferromagnetic transition changes in behavior with increasing pressure. This is caused by the monotonic reduction of the A coefficient in ρ(T)=ρ_{0}+AT with increasing pressure. The analysis of the pressure dependence of the resistivity strongly indicates that there is no enhancement of spin fluctuation in the vicinity of the pressure at which antiferromagnetism disappears. At the pressures where superconductivity occurs in the antiferromagnetic state, the ac susceptibility shows weak magnetic shielding with a large dissipation energy in the superconducting state. This probably indicates that the superconducting fluctuation is dominant under the magnetic order.©2012 The Physical Society of Japan

Specific-Heat Study of Superconducting and Normal States in FeSe_{1-x}Te_{x} (0.6≤x ≤1) Single Crystals: Strong-Coupling Superconductivity, Strong Electron-Correlation, and Inhomogeneity

2012-04-24T09:00:00+09:00

Authors: Takashi Noji, Masato Imaizumi, Takumi Suzuki, Tadashi Adachi, Masatsune Kato, and Yoji Koike
The electronic specific heat of as-grown and annealed single-crystals of FeSe_{1-x}Te_{x} (0.6≤x ≤1) has been investigated. It has been found that annealed single-crystals with x = 0.6–0.9 exhibit bulk superconductivity with a clear specific-heat jump at the superconducting (SC) transition temperature, T_{c}. Both 2Δ_{0}/k_{B}T_{c} [Δ_{0}: the SC gap at 0 K estimated using the single-band BCS s-wave model] and ΔC/(γ_{n}-γ_{0})T_{c} [ΔC: the specific-heat jump at T_{c}, γ_{n}: the electronic specific-heat coefficient in the normal state, γ_{0}: the residual electronic specific-heat coefficient at 0 K in the SC state] are largest in the well-annealed single-crystal with x = 0.7, i.e., 4.29 and 2.76, respectively, indicating that the superconductivity is of the strong coupling. The thermodynamic critical field has also been estimated. γ_{n} has been found to be one order of magnitude larger than those estimated from the band calculations and increases with increasing x at x = 0.6–0.9, which is surmised to be due to the increase in the electronic effective mass, namely, the enhancement of the electron correlation. It has been found that there remains a finite value of γ_{0} in the SC state even in the well-annealed single-crystals with x = 0.8–0.9, suggesting an inhomogeneous electronic state in real space and/or momentum space.©2012 The Physical Society of Japan

Charge and Spin Transport in Magnetic Tunnel Junctions: Microscopic Theory

Daisuke Miura and Akimasa Sakuma — 2012-04-24T09:00:00+09:00

Authors: Daisuke Miura and Akimasa Sakuma
We study the charge and spin currents passing through a magnetic tunnel junction (MTJ) on the basis of a tight-binding model. The currents are evaluated perturbatively with respect to the tunnel Hamiltonian. The charge current has the form \(A[\mathbf{M}_{1}(t)\times\dot{\mathbf{M}}_{1}(t)]\cdot\mathbf{M}_{2} + B\dot{\mathbf{M}}_{1}(t)\cdot\mathbf{M}_{2}\), where M_{1}(t) and M_{2} denote the directions of the magnetization in the free layer and fixed layer, respectively. The constant A vanishes when one or both layers are insulators, while the constant B disappears when both layers are insulators or the same ferromagnets. The first term in the expression for charge current represents dissipation driven by the effective electric field induced by the dynamic magnetization. In addition, from an investigation of the spin current, we obtain the microscopic expression for the enhanced Gilbert damping constant Δα. We show that Δα is proportional to the tunnel conductance and depends on the bias voltage.©2012 The Physical Society of Japan

Paramagnetic Metal–Antiferromagnetic Insulator Transition of λ-BETS_{2}Fe_{x}Ga_{1-x}Cl_{4} System

2012-04-23T09:00:00+09:00

Authors: Hiroshi Akiba, Hiroki Sugawara, Kento Nobori, Kazuo Shimada, Naoya Tajima, Yutaka Nishio, Koji Kajita, Biao Zhou, Akiko Kobayashi, and Hayao Kobayashi
The quasi-two-dimensional organic conductor λ-BETS_{2}FeCl_{4} [BETS = bis(ethylenedithio) tetraselenafulvalene] transforms from a paramagnetic metal (PM) to an antiferromagnetic insulator (AFI) at a transition temperature T_{MI} of 8.3 K under a zero magnetic field. To investigate the mechanism of this PM–AFI phase transition, we studied the Fe 3d spin content dependence of the AFI ground state by measuring the specific heat of the mixed crystal λ-BETS_{2}Fe_{x}Ga_{1-x}Cl_{4} at temperatures as low as 0.2 K. The increasing Fe 3d spin density enhances the internal magnetic field caused by π spin antiferromagnetic (AF) ordering. It was confirmed that the Fe 3d spin provides favorable conditions for this mysterious PM–AFI phase transition. We propose that this phase transition originates from the magnetic anisotropy introduced by the π–d interaction, which suppresses the low-dimensional fluctuation in the π spin system.©2012 The Physical Society of Japan

Time-Dependent Density-Matrix Approach to Collective Excitations of a Quantum Dot

Mitsuru Tohyama — 2012-04-23T09:00:00+09:00

Authors: Mitsuru Tohyama
We study collective excitations of a quantum dot consisting of two electrons using a time-dependent density-matrix approach. The advantages of the density-matrix approach are that one- and two-body observables are directly calculated using one- and two-body density matrices and that it has a clear relation to the time-dependent Hartree–Fock theory. Some low-lying spin modes associated with intrinsic transitions of a deformed configuration are predicted.©2012 The Physical Society of Japan

Subgrid-Scale Model for Reducing the Anisotropy of Turbulent Intensity in Channel Flow

Shoji Koyama — 2012-04-20T09:00:00+09:00

Authors: Shoji Koyama
Large-eddy simulation (LES) of a turbulent channel flow is carried out using a finite difference method (FDM) with a low order of accuracy. In this method, overestimation of turbulence anisotropy is a typical shortcoming. Since LES with the FDM is usually applied to practical cases, it is desirable to model the subgrid-scale (SGS) stress such that the problem is mitigated. Therefore, in this study two types of eddy-viscosity models are adopted and their influence on numerical results is investigated. Moreover, the redistribution term of turbulent energy is carefully examined through its co-spectrum. It is shown that the value of the high-wavenumber region plays an important role in improving the anisotropy.©2012 The Physical Society of Japan

Evidence of Spin-Filtering in Quantum Constrictions with Spin–Orbit Interaction

Sunwoo Kim, Yoshiaki Hashimoto, Yasuhiro Iye, and Shingo Katsumoto — 2012-04-20T09:00:00+09:00

Authors: Sunwoo Kim, Yoshiaki Hashimoto, Yasuhiro Iye, and Shingo Katsumoto
A new type of blockade effect – spin–orbit-induced blockade (SOIB) – has been observed in the conduction of a quantum dot (QD) made of a material with spin–orbit interaction. The blockade arises from the spin filtering effect in a quantum point contact (QPC), which is a component of the QD. Hence the appearance of the blockade itself is evidence of the spin filtering effect in the QPC. The lower bound of filtering efficiency is estimated to be above 80%.©2012 The Physical Society of Japan

A Consistent Description of Magnetic Properties of the Triangulated-Kagome System Cu_{9}X_{2}(cpa)_{6}·nH_{2}O

Makoto Isoda, Hiroki Nakano, and Tôru Sakai — 2012-04-19T09:00:00+09:00

Authors: Makoto Isoda, Hiroki Nakano, and Tôru Sakai
A consistent description of the behaviors of both the magnetic susceptibility and of the 1/3-plateau like magnetization under a magnetic field in the triangulated-kagome compound Cu_{9}X_{2}(cpa)_{6}·nH_{2}O (X = F, Cl, Br; cpa = the anion of 2-carboxypentonic acid) is given by the Heisenberg model with the antiferromagnetic next-nearest-neighbor interaction, in addition to the two types of antiferromagnetic nearest-neighbor interactions in previous studies. This description is provided by the method of numerical diagonalization. The newly introduced interaction derives the quantum phase transition from the quantum-disordered-state to the ferrimagnetic one. The stability of the magnetization plateaus is complemented using the perturbation theory.©2012 The Physical Society of Japan

On the Mechanism of Electrical Conduction in Cobalt-Doped Zinc Oxide Nanocrystalline Thin Films

Abdullah Yildiz and Felicia Iacomi — 2012-04-18T09:00:00+09:00

Authors: Abdullah Yildiz and Felicia Iacomi
ZnO and Co-doped ZnO thin films (3 and 11 at. %) were grown on glass substrates by spin coating method and structurally investigated by X-ray diffraction, X-ray photoelectron spectroscopy and UV–vis absorption spectroscopy. It was established that Co enters into ZnO wurtzite lattice by substitution. The electrical conductivity of undoped and Co-doped ZnO nanocrystalline thin films was measured in the temperature range of 300–425 K. The electrical conduction mechanism of the films is explained on the basis of the multiphonon assisted hopping model with a weak electron–phonon coupling. We found that the conductivity first increases with incorporation in ZnO structure of an amount of 3 at. % Co but then it decreases when the amount of Co is increased to 11 at. %. This situation is well explained by the fluctuation in the hopping rate.©2012 The Physical Society of Japan

Phase-Adjusting Layers in the Multilayer Reflector of a Jewel Beetle

Shinya Yoshioka, Shuichi Kinoshita, Haruhisa Iida, and Takahiko Hariyama — 2012-04-17T09:00:00+09:00

Authors: Shinya Yoshioka, Shuichi Kinoshita, Haruhisa Iida, and Takahiko Hariyama
In this study, we investigated the iridescence of a jewel beetle Chrysochroa fulgidissima, which is one of the most common examples of structural color produced by multilayer optical interference. We performed detailed measurements and analyses of angle- and polarization-dependent reflection spectra and found that a few layers located near the elytron surface play an important role in the coloration mechanism: they adjust the phases of light waves reflected from the lower part of the multilayer structure such that the waves interfere constructively with the reflection at the top surface. This phase adjustment is crucial to the coloration mechanism since the top surface contributes the most to the overall reflection owing to a large refractive-index difference between air and the cuticle. We also found that the jewel beetle exhibits a green-color-dominant iridescence: the blue color observed at oblique angles looks much weaker than the green color at small angles. We elucidated the physical origins of this peculiar iridescence by performing detailed analyses of the multilayer interference.©2012 The Physical Society of Japan

Multiferroicity on the Zigzag-Chain Antiferromagnet MnWO_{4} in High Magnetic Fields

2012-04-16T09:00:00+09:00

Authors: Hiroyuki Mitamura, Toshiro Sakakibara, Hiroyuki Nakamura, Tsuyoshi Kimura, and Koichi Kindo
The electric polarization and magnetization of the zigzag-chain antiferromagnet MnWO_{4} were measured in high pulsed magnetic fields of up to 53 T for the three principal directions x, y, and z, where x corresponds to the easy axis and y is the b^{*}-direction. In addition to the AF1, AF2, and HF phases already known, two magnetic phases, IV and V, successively appear in high magnetic fields for B∥x at 4.2 K. We found that phase IV is ferroelectric with the electric polarization P parallel to the b^{*}-axis, similar to the AF2 phase. It is also confirmed that phase IV is continuously connected to the previously reported X phase for the B∥y axis by changing the field direction. Interestingly, the successive field-induced phase transitions AF2–HF–IV in B∥x at a low temperature revealed that the signs of P∥b^{*} for AF2 and phase IV are always opposite each other, in spite of the intervening paraelectric HF phase extending to over 20 T. This result implies that an unusual memory effect is present in the HF phase. A model is given to explain the quasi-continuous AF2–IV transition at intermediate temperatures, accompanied by the inversion of P.©2012 The Physical Society of Japan

On the Classification of Fifth Order Quasi-linear Non-constant Separant Scalar Evolution Equations of the KdV-Type

Gülcan Özkum and Ayşe H Bilge — 2012-04-13T09:00:00+09:00

Authors: Gülcan Özkum and Ayşe H Bilge
Fifth order, quasi-linear, non-constant separant evolution equations are of the form \(u_{t} = A(\partial^{5}u/\partial x^{5}) + \tilde{B}\), where A and \(\tilde{B}\) are functions of x, t, u and of the derivatives of u with respect to x up to order 4. We use the existence of a “formal symmetry”, hence the existence of “canonical conservation laws” ρ_{(i)}, i = -1,...,5 as an integrability test. We define an evolution equation to be of the KdV-Type, if all odd numbered canonical conserved densities are nontrivial. We prove that fifth order, quasi-linear, non-constant separant evolution equations of KdV type are polynomial in the function a = A^{1/5}; a = (αu_{3}^{2} + βu_{3} + γ)^{-1/2}, where α, β, and γ are functions of x, t, u and of the derivatives of u with respect to x up to order 2. We determine the u_{2} dependency of a in terms of P = 4αγ- β^{2} > 0 and we give an explicit solution, showing that there are integrable fifth order non-polynomial evolution equations.©2012 The Physical Society of Japan

Antiferromagnetic Order and Superconductivity in Sr_{4}(Mg_{0.5-x}Ti_{0.5+x})_{2}O_{6}Fe_{2}As_{2} with Electron Doping: ^{75}As-NMR Study

2012-04-12T09:00:00+09:00

Authors: Keisuke Yamamoto, Hidekazu Mukuda, Hiroaki Kinouchi, Mitsuharu Yashima, Yoshio Kitaoka, Mamoru Yogi, Shinya Sato, Hiraku Ogino, and Jun-ichi Shimoyama
We report an ^{75}As-NMR study on iron (Fe)-based superconductors with thick perovskite-type blocking layers Sr_{4}(Mg_{0.5-x}Ti_{0.5+x})_{2}O_{6}Fe_{2}As_{2} with x=0 and 0.2. We have found that antiferromagnetic (AFM) order takes place when x=0, and superconductivity (SC) emerges below T_{c}=36 K when x=0.2. These results reveal that the Fe-pnictides with thick perovskite-type blocks also undergo an evolution from the AFM order to the SC by doping electron carriers into FeAs planes through the chemical substitution of Ti^{+4} ions for Mg^{+2} ions, analogous to the F-substitution in LaFeAsO compound. The normal-state property for x=0.2 unravels the suppression of AFM spin fluctuations at low energies, in contrast with the related Ca_{4}Al_{2}O_{6}Fe_{2}As_{2} with T_{c}=27 K, suggesting that the AFM spin fluctuations are not a unique factor for enhancing T_{c}. A condition for optimizing SC should be addressed from the relation with the local tetrahedron structure of FeAs_{4}.©2012 The Physical Society of Japan

Potential Antiferromagnetic Fluctuations in Hole-Doped Iron-Pnictide Superconductor Ba_{1-x}K_{x}Fe_{2}As_{2} Studied by ^{75}As Nuclear Magnetic Resonance Measurement

2012-04-12T09:00:00+09:00

Authors: Masanori Hirano, Yuji Yamada, Taku Saito, Ryo Nagashima, Takehisa Konishi, Tatsuya Toriyama, Yukinori Ohta, Hideto Fukazawa, Yoh Kohori, Yuji Furukawa, Kunihiro Kihou, Chul-Ho Lee, Akira Iyo, and Hiroshi Eisaki
We have performed ^{75}As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on single-crystalline Ba_{1-x}K_{x}Fe_{2}As_{2} for x = 0.27–1. ^{75}As nuclear quadruple resonance frequency (ν_{Q}) increases linearly with increasing x. The Knight shift K in the normal state shows Pauli paramagnetic behavior with a weak temperature T dependence. K increases gradually with increasing x. By contrast, the nuclear spin–lattice relaxation rate 1/T_{1} in the normal state has a strong T dependence, which indicates the existence of large antiferomagnetic (AF) spin fluctuations for all x's. The T dependence of 1/T_{1} shows a gaplike behavior below approximately 100 K for 0.6 < x < 0.9. This behaviors is well explained by the change in the band structure with the expansion of hole Fermi surfaces and the shrinkage and disappearance of electron Fermi surfaces at the Brillouin zone (BZ) with increasing x. The anisotropy of 1/T_{1}, represented by the ratio of 1/T_{1ab} to 1/T_{1c}, is always larger than 1 for all x's, which indicates that stripe-type AF fluctuations are dominant in this system. The K in the superconducting (SC) state decreases, which corresponds to the appearance of spin-singlet superconductivity. The T dependence of 1/T_{1} in the SC state indicates a multiple-SC-gap feature. A simple two-gap model analysis shows that the larger superconducting gap gradually decreases with increasing x from 0.27 to 1 and a smaller gap decreases rapidly and nearly vanishes for x > 0.6 where electron pockets in BZ disappear.©2012 The Physical Society of Japan

Erratum: “Spin–Orbit Interaction Enhanced Fractional Quantum Hall States in the Second Landau Level”

Toru Ito, Kentaro Nomura, and Naokazu Shibata — 2012-04-12T09:00:00+09:00

Authors: Toru Ito, Kentaro Nomura, and Naokazu Shibata

Optical Trapping of Nanoparticle near Metallic Plate by the Casimir Effect

Norio Inui — 2012-04-11T09:00:00+09:00

Authors: Norio Inui
We present a method of noncontact suspension of a nanoparticle near metallic plate in vacuum using the Casimir effect. Gravity can be balanced by an attractive Casimir force between a nanoparticle and a plate. Although the equilibrium position is unstable, it can be made pseudo-stable by optically controlling the Casimir force.©2012 The Physical Society of Japan

Anisotropic Spin-Fluctuations in SmCoPO Revealed by ^{31}P NMR Measurement

2012-04-11T09:00:00+09:00

Authors: Mayukh Majumder, Kajal Ghoshray, Amitabha Ghoshray, Anand Pal, and Veer P. S. Awana
^{31}P NMR spectral features in polycrystalline SmCoPO reveal an axially symmetric local magnetic field. At low temperature, the anisotropy of the internal magnetic field increases rapidly, with K_{ab} increasing faster than that of K_{c}. The dominant contribution to this anisotropy arises from Sm-4f electron contribution over that of Co-3d. The intrinsic width 2β deviates from linearity with respect to bulk susceptibility below 170 K due to the enhancement of (1/T_{2})_{dynamic}, which along with the continuous increase of anisotropy in the internal magnetic field is responsible for the wipe out effect of the NMR signal, well above T_{C}. 1/T_{1} shows large anisotropy confirming a significant contribution of Sm-4f electron spin fluctuations to 1/T_{1}, arising from indirect RKKY type exchange interaction indicating a non-negligible hybridization between Sm-4f orbitals and the conduction band, over the itinerant character of the Co-3d spins. This anisotropy originates from the orientation dependence of χ^{′′}(q,ω). The 3d-spin fluctuations in the ab-plane is 2D FM in nature, while along the c-axis, a signature of a weak AFM spin fluctuations superimposed on weak FM spin-fluctuations even in a field of 7 T and far above T_{N} is observed. The enhancement of this AFM fluctuations of the Co-3d spins along c-axis, at further low temperature is responsible to drive the system to an AFM ordered state.©2012 The Physical Society of Japan

How Are Heavy and Itinerant Electrons Born in a Dilute Kondo Alloy?

Yuji Matsumoto, Taichi Terashima, Shinya Uji, Noriaki Kimura, and Haruyoshi Aoki — 2012-04-11T09:00:00+09:00

Authors: Yuji Matsumoto, Taichi Terashima, Shinya Uji, Noriaki Kimura, and Haruyoshi Aoki
We report a continuous evolution of Fermi surface properties with temperature in a dilute Kondo alloy of Ce_{0.02}La_{0.98}Ru_{2}Si_{2} via measurements of the de Haas–van Alphen (dHvA) effect. The temperature variation of resistivity in this alloy exhibits a typical impurity Kondo behavior, i.e., the resistivity increases with decreasing temperature proportionally to -log T and becomes nearly constant below about 0.3 K. The Kondo temperature of this alloy is estimated to be about 1.3 K. The frequency of the dHvA oscillation from the main hole surface decreases with decreasing temperature implying that the hole surface shrinks with decreasing temperature. The temperature dependence of the frequency change is found to be similar to that of resistivity. The temperature dependence of this dHvA oscillation amplitude deviates largely from that expected from the Lifshitz–Kosevich formula conventionally employed to determine the effective mass from the temperature dependence. By assuming that the scattering of the conduction electron increases with decreasing temperature in the same manner as that of resistivity and that the effective mass increases with decreasing temperature, the anomalous temperature dependence can be explained. From these observations we argue that the f electron nature changes from localized at high temperatures to itinerant at low temperatures resulting in the change of the Fermi surface volume and the increase in the effective mass. The effective mass of this oscillation is determined from the temperature dependence at the lowest temperatures below 0.3 K to be about 3.8 m_{0}, which is considerably larger than 1.6 m_{0} of the corresponding oscillation in LaRu_{2}Si_{2} but seems to be much smaller than that expected from the Kondo temperature of this alloy.©2012 The Physical Society of Japan

Correspondence between Magic Numbers and Electron Degeneracy in Alkali Clusters

Kohji Sonoda — 2012-04-11T09:00:00+09:00

Authors: Kohji Sonoda

Ab-initio Study of Interactions of Gold Atoms with Hydroxylated MgO(001) Surfaces

2012-04-09T09:00:00+09:00

Authors: Junjin Jeon, Aloysius Soon, Jin-Nam Yeo, Jinwoo Park, Suklyun Hong, Kyeongjae Cho, and Byung Deok Yu
By employing ab-initio electronic structure calculations based on the density functional theory, we investigated the adsorption, diffusion, bonding, and electronic properties associated with the enhanced bonding of Au on hydroxylated MgO(001) surfaces. The calculations in this study show that the binding of Au on hydroxylated MgO(001) is substantially enhanced by an ionic-like interaction as compared to the case of Au on regular MgO(001). Indeed, the adsorption of Au on hydroxylated MgO surfaces is stronger than that of Au and OH on MgO(001). AuOH complexes are formed on MgO(001) surfaces via the fast surface diffusion of OH and Au. It is found that the AuOH structure is very stable against not only dissociation (i.e., it is very difficult for it to decompose back into OH and Au) but also surface diffusion (i.e., it has low surface mobility). More detailed electronic structure analysis of the charge distribution of AuOH on MgO(001) reveals that the enhanced ionic-like bonding is achieved via the polarization variation in Au induced by both ionic OH and MgO surface atoms.©2012 The Physical Society of Japan

Different High-Temperature Spin Dynamics of Ising Pyrochlore Dy_{2}Sn_{2}O_{7} and Heisenberg Pyrochlore Gd_{2}Sn_{2}O_{7}

2012-04-09T09:00:00+09:00

Authors: Tomomi Kaibuchi, Hiroshi Tashiro, Tetsuaki Itou, Masahide Nishiyama, Akira Oyamada, Satoru Maegawa, and Kazuyuki Matsuhira
We measured the nuclear magnetic spin–lattice (T_{1}^{-1}) and spin–spin (T_{2}^{-1}) relaxation rates of ^{119}Sn nuclei of the Ising pyrochlore magnet Dy_{2}Sn_{2}O_{7} and the Heisenberg pyrochlore magnet Gd_{2}Sn_{2}O_{7} at high temperatures (120–294 K for Dy_{2}Sn_{2}O_{7} and 20–284 K for Gd_{2}Sn_{2}O_{7}) to investigate their high-temperature 4f-electron spin dynamics. We found the following two results, which reveal remarkable differences between the spin dynamics of Dy_{2}Sn_{2}O_{7} and Gd_{2}Sn_{2}O_{7}. First, the ratio T_{2}^{-1}/T_{1}^{-1} for powder samples is almost unity in Dy_{2}Sn_{2}O_{7}, whereas it is about 6 in Gd_{2}Sn_{2}O_{7}. Second, these relaxation rates increase markedly on cooling in Dy_{2}Sn_{2}O_{7}, reflecting thermal activation with a gap of ∼600 K, whereas they are almost constant with temperature in Gd_{2}Sn_{2}O_{7}. The former result indicates that spin fluctuations of Dy_{2}Sn_{2}O_{7} are completely restricted to the <111 > direction, whereas Gd spins fluctuate three-dimensionally and the component of the fluctuations parallel to an externally applied field contributes to the nuclear relaxation rates in Gd_{2}Sn_{2}O_{7}. The latter result indicates that the spin fluctuations of Dy_{2}Sn_{2}O_{7} are caused by an indirect spin-flip process mediated through an excited state of the crystalline electric field multiplets, whereas those of Gd_{2}Sn_{2}O_{7} are dominated by the direct mutual spin-flip process by interactions between 4f-electron spins.©2012 The Physical Society of Japan

Erratum: “Zero-Collision Term Problem in Kinetic Theory of One-Dimensional Systems”

Mitsusada M. Sano — 2012-04-09T09:00:00+09:00

Authors: Mitsusada M. Sano

Superconductivity Induced by Bond Breaking in the Triangular Lattice of IrTe_{2}

Sunseng Pyon, Kazutaka Kudo, and Minoru Nohara — 2012-04-06T09:00:00+09:00

Authors: Sunseng Pyon, Kazutaka Kudo, and Minoru Nohara
IrTe_{2}, a layered compound with a triangular iridium lattice, exhibits a structural phase transition at approximately 250 K. This transition is characterized by the formation of Ir–Ir bonds along the b-axis. We found that the breaking of Ir–Ir bonds that occurs in Ir_{1-x}Pt_{x}Te_{2} results in the appearance of a structural critical point in the T = 0 limit at x_{c}≃0.035. Although both IrTe_{2} and PtTe_{2} are paramagnetic metals, superconductivity at T_{c} = 3.1 K is induced by the bond breaking in a narrow range of x≥x_{c} in Ir_{1-x}Pt_{x}Te_{2}. This result indicates that structural fluctuations can be involved in the emergence of superconductivity.©2012 The Physical Society of Japan

Recent articles in J. Phys. Soc. Jpn.

Experimental and Theoretical Investigations of the Negative Differential Resistance in a Discharge Plasma

Writing Nanowires with Large Conductivity Ratios in LaAlO_{3}/SrTiO_{3} Interfaces

Superconductivity in Pt Doped BaFe_{2}As_{2}

Quantum Hall Effects in Silicene

Formation of Step Bunches Induced by Flow in Solution

Magnetic Structure of SrCo_{3}P_{4}O_{14} Determined from Neutron Powder Diffraction Results

Field-Induced Magnetostructural Transitions in Antiferromagnetic Fe_{1+y}Te_{1-x}S_{x}

Analysis of XY Model with Mexican-Hat Interaction on a Circle –Derivation of Saddle Point Equations and Study of Bifurcation Structure–

Low-Temperature Properties of the Fermionic Mixtures with Mass Imbalance in Optical Lattice

Transformation of the Transverse Beam Intensity Distribution by Sextupole Focusing in a Transport Line

Low-Energy Effective Hamiltonian and the Surface States of Ca_{3}PbO

Mott Transition and Spin Structures of Spin-1 Bosons in Two-Dimensional Optical Lattice at Unit Filling

Quantum Limiting Behaviors of a Vortex Core in an Anisotropic Gap Superconductor

Study of Neutron Diffraction on ^{154}SmRu_{4}P_{12} Single Crystal

Explicit Expression for Steady Plane Irrotational Incompressible Flow around Obstacles

Spin and Chiral Orderings of the Antiferromagnetic XY Model on the Triangular Lattice and Their Critical Properties

Comment on “Details of Sample Dependence and Transport Properties of URu_{2}Si_{2}”

Reply to “Comment on `Details of Sample Dependence and Transport Properties of URu_{2}Si_{2}”'

Analysis of C V Ions by Measuring Line Ratios in the LHD

Observation of Structural Change in the Novel Ferromagnetic Metal–Insulator Transition of K_{2}Cr_{8}O_{16}

Absence of Quantum Criticality and Presence of Superconducting Fluctuation in Pressure-Induced Heavy-Fermion Superconductor CeRhSi_{3}

Specific-Heat Study of Superconducting and Normal States in FeSe_{1-x}Te_{x} (0.6≤x ≤1) Single Crystals: Strong-Coupling Superconductivity, Strong Electron-Correlation, and Inhomogeneity

Charge and Spin Transport in Magnetic Tunnel Junctions: Microscopic Theory

Paramagnetic Metal–Antiferromagnetic Insulator Transition of λ-BETS_{2}Fe_{x}Ga_{1-x}Cl_{4} System

Time-Dependent Density-Matrix Approach to Collective Excitations of a Quantum Dot

Subgrid-Scale Model for Reducing the Anisotropy of Turbulent Intensity in Channel Flow

Evidence of Spin-Filtering in Quantum Constrictions with Spin–Orbit Interaction

A Consistent Description of Magnetic Properties of the Triangulated-Kagome System Cu_{9}X_{2}(cpa)_{6}·nH_{2}O

On the Mechanism of Electrical Conduction in Cobalt-Doped Zinc Oxide Nanocrystalline Thin Films

Phase-Adjusting Layers in the Multilayer Reflector of a Jewel Beetle

Multiferroicity on the Zigzag-Chain Antiferromagnet MnWO_{4} in High Magnetic Fields

On the Classification of Fifth Order Quasi-linear Non-constant Separant Scalar Evolution Equations of the KdV-Type

Antiferromagnetic Order and Superconductivity in Sr_{4}(Mg_{0.5-x}Ti_{0.5+x})_{2}O_{6}Fe_{2}As_{2} with Electron Doping: ^{75}As-NMR Study

Potential Antiferromagnetic Fluctuations in Hole-Doped Iron-Pnictide Superconductor Ba_{1-x}K_{x}Fe_{2}As_{2} Studied by ^{75}As Nuclear Magnetic Resonance Measurement

Erratum: “Spin–Orbit Interaction Enhanced Fractional Quantum Hall States in the Second Landau Level”

Optical Trapping of Nanoparticle near Metallic Plate by the Casimir Effect

Anisotropic Spin-Fluctuations in SmCoPO Revealed by ^{31}P NMR Measurement

How Are Heavy and Itinerant Electrons Born in a Dilute Kondo Alloy?

Correspondence between Magic Numbers and Electron Degeneracy in Alkali Clusters

Ab-initio Study of Interactions of Gold Atoms with Hydroxylated MgO(001) Surfaces

Different High-Temperature Spin Dynamics of Ising Pyrochlore Dy_{2}Sn_{2}O_{7} and Heisenberg Pyrochlore Gd_{2}Sn_{2}O_{7}

Erratum: “Zero-Collision Term Problem in Kinetic Theory of One-Dimensional Systems”

Superconductivity Induced by Bond Breaking in the Triangular Lattice of IrTe_{2}