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Journal Articles

Kondo effect driven by chirality imbalance

Suenaga, Daiki*; Suzuki, Kei; Araki, Yasufumi; Yasui, Shigehiro*

Physical Review Research (Internet), 2(2), p.023312_1 - 023312_13, 2020/06

The Kondo effect is induced by the interaction between light fermions near the Fermi surface and heavy impurities, and it affects electric/thermal/transport properties of matter. The chirality (right-handed or left-handed) is one of the unique properties of relativistic (Dirac or Weyl) fermions. In normal matter, the numbers of right- and left-handed particles are equivalent to each other, but environments with a chirality imbalance can also be realized. In this paper, we theoretically propose the Kondo effect driven by a chirality imbalance (or chiral chemical potential) of relativistic light fermions. This effect is caused by the mixing between a right-handed (or left-handed) fermion and a heavy impurity in the chirality imbalanced matter. This is different from the usual Kondo effect induced by finite density (or chemical potential) for light fermions. We construct an effective model with an interaction between a relativistic fermion and a heavy impurity, and we derive the realization of the Kondo effect from both a perturbative calculation and a nonperturbative mean-field approach. We also discuss the temperature dependence, the coupling constant dependence, the susceptibilities, and the order of the phase transition for the Kondo effect. Such a Kondo effect will be tested by future lattice simulations.

Journal Articles

QCD Kondo excitons

Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*

Physical Review Research (Internet), 2(2), p.023066_1 - 023066_11, 2020/04

The QCD Kondo effect is a quantum phenomenon in which heavy (charm or bottom) quarks exist as impurity particles in quark matter composed of light quarks at extremely high density. In this paper, we theoretically predict the existence of the exciton modes above the ground state of the quark matter governed by the QCD Kondo effect. We construct an effective model based on the mean field approximation and investigate possible quantum numbers (such as spin and parity) of excitons and their dispersion relations. These excitons can be electrically (color) neutral, so that they are observed as the neutral currents in transport phenomena. As a result, they contribute to violation of the Wiedemann-Franz law for the electric (color) and heat conductivities. Such Kondo excitons are an universal phenomenon for relativistic (Dirac or Weyl) fermions, and the same concept will also be applied to Dirac or Weyl electron systems.

Journal Articles

Study of negative hydrogen ion beam optics using the 2D PIC method

Miyamoto, Kenji*; Okuda, Shin*; Hatayama, Akiyoshi*; Hanada, Masaya; Kojima, Atsushi

AIP Conference Proceedings 1515, p.22 - 30, 2013/02

 Times Cited Count:8 Percentile:4.33

We have developed the integrated 2D PIC code for the analysis of the negative ion beam optics, in which an overall region from the source plasma to the accelerator is modeled. Thus, the negative ion trajectory can be solved self-consistently without any assumption of the plasma meniscus form initially. This code can reproduce the negative ion beam halo observed in an actual negative ion beam. It is confirmed that the surface produced negative ions which are extracted near the edge of the meniscus can be one of the reasons for the beam halo: these negative ions are over-focused due to the curvature of the meniscus. The negative ions are not focused by the electrostatic lens, and consequently become the beam halo.

Journal Articles

Study of plasma meniscus formation and beam halo in negative hydrogen ion sources

Okuda, Shin*; Miyamoto, Kenji*; Fukuyama, Toshishige*; Nishioka, Shu*; Hatayama, Akiyoshi*; Fukano, Azusa*; Hanada, Masaya; Kojima, Atsushi

AIP Conference Proceedings 1515, p.107 - 113, 2013/02

 Times Cited Count:9 Percentile:3.53

A meniscus of plasma-beam boundary in H$$^{-}$$ ion sources largely affects the extracted H$$^{-}$$ ion beam optics. Recently it is shown that the beam halo is mainly caused by the meniscus, i.e. ion emissive surface, close to the plasma grid (PG) where its curvature is large. The purpose of this study is to clarify the effect of H$$^{-}$$ surface production rate on plasma meniscus and beam halo formation with PIC (particle-in-cell) modeling. It is shown that the plasma meniscus and beam halo formation is strongly dependent on the amount of surface produced H$$^{-}$$ ions.

Journal Articles

Study of beam optics and beam halo by integrated modeling of negative ion beams from plasma meniscus formation to beam acceleration

Miyamoto, Kenji*; Okuda, Shin*; Hatayama, Akiyoshi*; Hanada, Masaya; Kojima, Atsushi

Applied Physics Letters, 102(2), p.023512_1 - 023512_4, 2013/01

 Times Cited Count:18 Percentile:30.68(Physics, Applied)

To understand the physical mechanism of the beam halo formation in negative ion beams, a two-dimensional particle-in-cell code for simulating the trajectories of negative ions created via surface production has been developed. The simulation code reproduces a beam halo observed in an actual negative ion beam. The negative ions extracted from the periphery of the plasma meniscus (an electro-static lens in a source plasma) are over-focused in the extractor due to large curvature of the meniscus.

Journal Articles

Numerical analysis of surface produced H$$^{-}$$ ions by using two-dimensional particle-in-cell method

Miyamoto, Kenji*; Okuda, Shin*; Hatayama, Akiyoshi*; Hanada, Masaya

Review of Scientific Instruments, 83(2), p.02A723_1 - 02A723_4, 2012/02

 Times Cited Count:8 Percentile:55.01(Instruments & Instrumentation)

The modeling and analysis of a negative ion source is proceeding by using a 2D particle-in-cell simulation. The effect of the H$$^{-}$$ ion production on the plasma grid (PG) surface is investigated. It is shown that with the increase of H$$^{-}$$ ions per time step, the H$$^{-}$$ ion current density is enhanced, while the electron current density decreases with increasing the H$$^{-}$$ production rate on the PG surface. Theseresults agree well with the experimental results observed in typical negative ion sources. Moreover, it is found that plasma quasi-neutrality is held mainly by both H$$^{+}$$ and H$$^{-}$$ ions in the bulk plasma.

Journal Articles

Simulation on nanostructured metals based on multiscale crystal plasticity considering effect of grain boundary

Aoyagi, Yoshiteru; Shimokawa, Tomotsugu*; Shizawa, Kazuyuki*; Kaji, Yoshiyuki

Materials Science Forum, 706-709, p.1751 - 1756, 2012/01

 Times Cited Count:1 Percentile:35.41

In this study, we develop a crystal plasticity model considering an effect of grain boundary. In order to predict increase of local critical resolved shear stress due to existence of grain boundaries, information of grain boundary as a role of dislocation sources is introduced into a hardening law of crystal plasticity. In addition, carrying out FE simulation for plastic deformation of FCC polycrystal, the stress-strain responses such as increase of yield stress due to existence of grain boundary are discussed. We investigate comprehensively the effect of dislocation behavior on the material property of nanostructured metal. The increase of yield stress and the decrease of hardening ratio with the reduction of grain size are caused by local differences on CRSS and dislocation behavior, respectively.

Journal Articles

A Multiscale crystal plasticity simulation on ultrafine-graining based on dislocation patterning

Aoyagi, Yoshiteru; Kobayashi, Ryotaro*; Shizawa, Kazuyuki*

Nippon Kikai Gakkai Rombunshu, A, 77(775), p.448 - 461, 2011/03

Ultrafine-grained metals whose grain size is less than one micron have attracted interest as high strength materials. However, a mechanism of ultrafine-graining based on evolution of dislocation structures has not been clarified. In this study, we derive reaction-diffusion equations for dislocation patterning of dislocation cell structures and subgrains. In order to express the generation of dislocation pattern responding to deformation progress, information of slip rate and stress and effect of interactions between slip systems on formation of cell structures are introduced into the reaction rate coefficients of reaction-diffusion equations. Moreover, we propose a multiscale crystal plasticity model based on dislocation patterning. Then we carry out two-dimensional FE-FD simulation for severe compression of FCC polycrystal using the present model. Some processes of ultrafine-graining, i.e., generation of dislocation cell structures, subgrains, dense dislocation walls and lamella subdivisions with high angle boundary is numerically reproduced, and we investigate the effect of dislocation behaviors on the processes of ultrafine-graining.

Journal Articles

A Triple-scale dislocation-crystal plasticity simulation on yield point drop of annealed FCC ultrafine-grained metal

Kurosawa, Eisuke*; Aoyagi, Yoshiteru; Shizawa, Kazuyuki*

Nippon Kikai Gakkai Rombunshu, A, 76(772), p.1547 - 1556, 2010/12

In order to express the increase of critical resolved shear stress, the conventional Bailey-Hirsh's relationship is extended on the basis of physical consideration for grain boundary that plays a role of dislocation source. A triple-scale dislocation-crystal plasticity FE simulation based on the above model, geometrically necessary crystal defects and the homogenization method is carried out for annealed FCC polycrystals with different initial grain size and initial dislocation density. Yield point drop and propagation of L$"{u}$ders bands observed in macroscopic specimen with annealed FCC fine-grains are numerically reproduced. Moreover, macroscopic yielding of specimen and microscopic grain yielding are investigated in detail so as to clarify the initial yield behavior of annealed ultrafine-grained metals. It is also shown that plastic deformation is easy to be localized and the tensile ductility decreases as the grain size reduces.

Journal Articles

X-ray photon correlation spectroscopy study in valence fluctuation compound Eu$$_{3}$$S$$_{4}$$

Nakao, Hironori*; Owada, Kenji; Shimomura, Susumu*; Ochiai, Akira*; Namikawa, Kazumichi*; Mizuki, Junichiro; Mimura, Hidekazu*; Yamauchi, Kazuto*; Murakami, Yoichi*

AIP Conference Proceedings 1234, p.935 - 938, 2010/06

 Times Cited Count:2 Percentile:28.89

Journal Articles

X-ray intensity fluctuation spectroscopy using nanofocused hard X-rays; Its application to study of relaxor ferroelectrics

Owada, Kenji; Namikawa, Kazumichi*; Shimomura, Susumu*; Nakao, Hironori*; Mimura, Hidekazu*; Yamauchi, Kazuto*; Matsushita, Mitsuyoshi*; Mizuki, Junichiro

Japanese Journal of Applied Physics, 49(2), p.020216_1 - 020216_3, 2010/02

 Times Cited Count:3 Percentile:82.75(Physics, Applied)

Journal Articles

Effects of chemical bonding character on pressure-induced structural changes of liquid metals and semiconductors

Hattori, Takanori; Tsuji, Kazuhiko*

Materia, 47(10), p.507 - 512, 2008/10

We investigate pressure-induced structural changes in liquids of tetrahedrally bonded materials by a synchrotron X-ray diffraction. The liquids show various structural changes, depending on their ionic characters in the chemical bonds. The liquids with a small ionic character, such as GaSb, InSb, InAs, show continuous structural changes over a wide pressure region of about 20 GPa. In contrast, those with a large ionic character, such as CdTe, AgI, show drastic structural changes within a narrow pressure region of $$sim$$ 2 GPa. We discuss the effect of the ionicity on the pressure-induced structural changes in liquid and compare the effect with that in the crystalline phases.

JAEA Reports

Spatial uniformity of negative ion beam in magnetically filtered hydrogen negative ion source; Effect of the H$$^{-}$$ ion production and transport processes on the H$$^{-}$$ ion beam intensity profile in the Cs-seeded negative ion source (Joint research)

Takato, Naoyuki; Tobari, Hiroyuki; Inoue, Takashi; Hanada, Masaya; Seki, Takayoshi*; Kato, Kyohei*; Hatayama, Akiyoshi*; Sakamoto, Keishi

JAEA-Research 2008-031, 44 Pages, 2008/03

JAEA-Research-2008-031.pdf:4.05MB

The origin of the H$$^{-}$$ ion beam non-uniformity under the Cesium seeded condition was studied in the JAEA 10 Ampere negative ion source by measuring the profiles of the beam intensity and plasma parameters. The numerical analyses, such as the trace of particles (the electron, the H$$^{0}$$ atom and the H$$^{-}$$ ion) trajectories using the Monte Carlo method, were also applied to consider the experimental results.

Journal Articles

Numerical analysis of the production profile of H$$^{0}$$ atoms and subsequent H$$^{-}$$ ions in large negative ion sources

Takado, Naoyuki*; Tobari, Hiroyuki; Inoue, Takashi; Hanatani, Junji*; Hatayama, Akiyoshi*; Hanada, Masaya; Kashiwagi, Mieko; Sakamoto, Keishi

Journal of Applied Physics, 103(5), p.053302_1 - 053302_12, 2008/03

 Times Cited Count:22 Percentile:32.51(Physics, Applied)

The production and transport processes of H$$^{0}$$ atoms are numerically simulated using a three-dimensional Monte Carlo transport code. The code was applied to the large JAEA 10 ampere negative ion source under the Cs-seeded condition to obtain a spatial distribution of surface-produced H$$^{-}$$ ions. In the H$$^{0}$$ atom transport process, the energy relaxation of the H$$^{0}$$ atoms, which affects the surface H$$^{-}$$ ion production rate, is taken into account. The result indicates that the surface H$$^{-}$$ ion production is enhanced near the high-electron-temperature region where H$$^{0}$$ atom production is localized.

Journal Articles

Effect of energy relaxation of H$$^{0}$$ atoms at the wall on the production profile of H$$^{-}$$ ions in large negative ion sources

Takado, Naoyuki*; Matsushita, Daisuke*; Fujino, Ikuro*; Hatayama, Akiyoshi*; Tobari, Hiroyuki; Inoue, Takashi

Review of Scientific Instruments, 79(2), p.02A503_1 - 02A503_4, 2008/02

 Times Cited Count:2 Percentile:84.01(Instruments & Instrumentation)

Production and transport process of the H$$^{0}$$ atoms are numerically simulated using a three-dimensional Monte Carlo transport code. The code was applied to the "JAEA 10 ampere negative ion source" under Cs-seeded condition to obtain a spatial distribution of surface-produced H$$^{0}$$ ions. In this analysis, we focus on the effect of the energy relaxation of the H$$^{0}$$ atoms at the wall on the H$$^{-}$$ ion production from the H$$^{0}$$ atoms. The result indicates that, by considering the energy relaxation of the H$$^{0}$$ atoms at the wall, the production profile of the surface-produced H$$^{-}$$ ion is well reflected in the production profile of the H$$^{0}$$ atom production.

Journal Articles

Numerical analysis of H$$^{-}$$ ion transport processes in Cs-seeded negative ion sources

Matsushita, Daisuke*; Takado, Naoyuki*; Hatayama, Akiyoshi*; Inoue, Takashi

Review of Scientific Instruments, 79(2), p.02A527_1 - 02A527_4, 2008/02

 Times Cited Count:5 Percentile:68.54(Instruments & Instrumentation)

The H$$^{-}$$ ion transport processes are numerically simulated to understand the extraction process of surface-produced H$$^{-}$$ ions. The three-dimensional transport code using Monte Carlo method has been applied to calculate the H$$^{-}$$ ion extraction probabilities in the model geometry of the JAEA 10 ampere negative ion source. The roles of (1) filter magnetic field and (2) collisions with neutrals (H$$^{0}$$ atoms and H$$_{2}$$ molecules) on the H$$^{-}$$ ion extraction are systematically studied. The results show that H$$^{-}$$ ions are extracted mainly by the filter magnetic field under the low gas pressure condition. The simulation results of extracted H$$^{-}$$ ion beam intensity in the JAEA 10 ampere negative ion source without the magnetic filter tend to be smaller than the experimental results, especially under the low pressure condition.

Journal Articles

Analysis of electron energy distribution of an arc-discharge H$$^{-}$$ ion source with Monte Carlo simulation

Fujino, Ikuro*; Hatayama, Akiyoshi*; Takado, Naoyuki*; Inoue, Takashi

Review of Scientific Instruments, 79(2), p.02A510_1 - 02A510_3, 2008/02

 Times Cited Count:21 Percentile:29.86(Instruments & Instrumentation)

For optimization and accurate prediction of the amount of H$$^{-}$$ ion production in negative ion source, analysis of electron energy distribution function (EEDF) is necessary. We developed a numerical code which analyzes EEDF in the tandem-type arc discharge source. It is a three-dimensional Monte Carlo simulation code with the effects of cusp, filter, and extraction magnets. Coulomb collision between electrons is treated with Takizuka's model and several inelastic collisions are treated with null-collision method. We applied this code to the JAEA 10 ampere negative ion source. As a result, the order of electron density is in good agreement with experimental results. In addition, the obtained EEDF is qualitatively in good agreement with experimental results.

Journal Articles

Numerical analysis of the hydrogen atom density in a negative ion source

Takato, Naoyuki; Hanatani, Junji*; Mizuno, Takatoshi*; Hatayama, Akiyoshi*; Tobari, Hiroyuki; Hanada, Masaya; Inoue, Takashi; Taniguchi, Masaki; Dairaku, Masayuki; Kashiwagi, Mieko; et al.

AIP Conference Proceedings 925, p.38 - 45, 2007/09

The production and transport processes of the H$$^0$$ atom are numerically simulated to obtain the H$$^0$$ atom density. The three dimensional transport code using the Monte Carlo method has been applied to H$$^0$$ atoms in the large "JAEA 10 ampere negative ion source" under the Cs-seeded condition. In this study, the production rate of H$$^0$$ atoms through the dissociation process of H$$_2$$ molecules is estimated from single probe characteristics of the Langmuir probe measurement. In addition, the energy relaxation process of H$$^0$$ atoms is also considered. The results show that the existence of high-energy electrons and the energy relaxation process of H$$^0$$ atoms affect the H$$^0$$ atom density.

Journal Articles

Pressure dependence of the structure of liquid Sn up to 19.4 GPa

Narushima, Takashi*; Hattori, Takanori; Kinoshita, Tomohiro*; Hinzmann, A*; Tsuji, Kazuhiko*

Physical Review B, 76(10), p.104204_1 - 104204_8, 2007/09

 Times Cited Count:19 Percentile:34.42(Materials Science, Multidisciplinary)

The structure of liquid Sn was investigated up to 19.4 GPa by synchrotron X-ray diffraction. Upon compression up to about 3-6 GPa, the structural features, which reflect the anisotropic local structure become less prominent; i.e., the hump on the high-$$Q$$ side of the first peak in the structure factor $$S(Q)$$ becomes smaller, the position of the second peak relative to that of the first peak in $$S(Q)$$, $$Q_{2}/Q_{1}$$, decreases, and the coordination number, CN, increases. These features indicate that the liquid structure changes toward a simple liquid metal upon compression. However, at higher pressures, the structural parameters nearly unchanged. The parameters in this pressure range are still deviated from their respective values for simple liquid metals. These findings suggest that, contrary to previous expectations, the liquid does not monotonically approach a simple liquid metal, but takes a relatively stable intermediate form with an anisotropic local structure before approaching a simple liquid metal. The high-pressure behavior of liquid Sn is compared to those of liquid Si and liquid Ge and the systematics in liquid group 14 elements are discussed.

Journal Articles

Experimental evidence for ferromagnetic spin-pairing superconductivity emerging in UGe$$_2$$; A $$^{73}$$Ge-nuclear-quadrupole-resonance study under pressure

Harada, Atsushi*; Kawasaki, Shinji*; Mukuda, Hidekazu*; Kitaoka, Yoshio*; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika; Ito, Kohei*; Haller, E. E.*; Harima, Hisatomo*

Physical Review B, 75(14), p.140502_1 - 140502_4, 2007/04

 Times Cited Count:26 Percentile:26.31(Materials Science, Multidisciplinary)

This paper reports that a different type of superconducting order parameter has been realized in the ferromagnetic states in UGe$$_2$$ via $$^{73}$$Ge-nuclear-quadrupole-resonance experiments performed under pressure. Measurements of the nuclear spin-lattice relaxation rate (1/$$T$$$rm$_1$$) have revealed an unconventional nature of superconductivity such that the up-spin band is gapped with line nodes, but the down-spin band remains gapless at the Fermi level. This result is consistent with that of a ferromagnetic spin-pairing model in which Cooper pairs are formed among ferromagnetically polarized electrons. The present experiment has shed light on the possible origin of ferromagnetic superconductivity, which is mediated by ferromagnetic spin-density fluctuations relevant to the first-order transition inside the ferromagnetic states.

36 (Records 1-20 displayed on this page)