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Tonegawa, Takashi*; Okamoto, Kiyomi*; Hikihara, Toshiya*; Sakai, Toru
Journal of Physics; Conference Series, 683(1), p.012039_1 - 012039_7, 2016/02
Times Cited Count：2 Percentile：69.77(Materials Science, Multidisciplinary)Employing mainly numerical methods, we explore the ground-state phase diagram of an anisotropic S=1/2 ladder, in which leg interactions are uniform and isotropic, while rung interactions are alternating and have a common Ising-type anisotropy. We determine the phase diagrams in some typical cases.
Okamoto, Kiyomi*; Tonegawa, Takashi*; Sakai, Toru
Journal of Physics; Conference Series, 683(1), p.012038_1 - 012038_6, 2016/02
Times Cited Count：2 Percentile：69.77(Materials Science, Multidisciplinary)By use of mainly the exact diagonalization and the level spectroscopy method, we investigate the ground-state phase diagrams of the S=1/2 distorted diamond type quantum spin chain with the monomer-monomer interactions and ferromagnetic interactions. The magnetization plateau at 1/3 of the saturation magnetization was revealed to vanish in the region where the ferromagnetic interaction is rather strong.
Okamoto, Kiyomi*; Tonegawa, Takashi*; Sakai, Toru; Kaburagi, Makoto*
JPS Conference Proceedings (Internet), 3, p.014022_1 - 014022_7, 2014/06
The S=2 quantum spin chain with the XXZ anisotropy and the on-site anisotropy is investigated by the numerical diagonalization and density matrix renormalization group analysis. As a result, it was found that an edge mode appears in the intermediate-D phase, while not in the large-D phase.
Sakai, Toru; Okamoto, Kiyomi*
JPS Conference Proceedings (Internet), 1, p.012025_1 - 012025_4, 2014/03
The spin nanotubes are theoretically investigated by the numerical diagonalization and the density matrix renormalization group calculation. As a result, it is found that a quantum phase transition from the spin gapped to the gapless phases is induced by the lattice distortion. We also discuss about a possible superconductivity induced by the chirality degrees of freedom.
Sakai, Toru; Okamoto, Kiyomi*
JPS Conference Proceedings (Internet), 2, p.010208_1 - 010208_4, 2014/03
The magnetism of the S=1/2 quantum spin nanotube is investigated by the numerical diagonalization and phenomenological renormalization. As a result, it was found that a novel quantum phase transition occurs between the gapped and gapless phases, with respect to the anisotropy.
Sakai, Kenji; Sakamoto, Shinichi; Kinoshita, Hidetaka; Seki, Masakazu; Haga, Katsuhiro; Kogawa, Hiroyuki; Wakui, Takashi; Naoe, Takashi; Kasugai, Yoshimi; Tatsumoto, Hideki; et al.
JAEA-Technology 2011-039, 121 Pages, 2012/03
JAEA-Technology-2011-039.pdf:10.87MB
This report investigates the behavior, damage and restoration of a neutron source station of the MLF at the Great East Japan Earthquake and verified the safety design for emergency accidents in the neutron source station. In the MLF, after an occurrence of the Earthquake, strong quakes were detected at the instruments, the external power supply was lost, all of the circulators shut down automatically, and the hydrogen gas was released. The leakages of mercury, hydrogen and radio-activation gases did not occur. While, the quakes made gaps between the shield blocks and ruptured external pipe lines by subsidence around the building. But significant damages to the components were not found though the pressure drop of compressed air lines influenced on a target trolley lock system and so on. These results substantiated the validity of the safety design for emergency accidents in the source station, and suggested several points of improvement.
Sakai, Kenji; Futakawa, Masatoshi; Takada, Hiroshi; Sakamoto, Shinichi; Maekawa, Fujio; Kinoshita, Hidetaka; Seki, Masakazu; Haga, Katsuhiro; Kogawa, Hiroyuki; Wakui, Takashi; et al.
Proceedings of 20th Meeting of the International Collaboration on Advanced Neutron Sources (ICANS-20) (USB Flash Drive), 6 Pages, 2012/03
This report investigates behaviors and damages of each component in a neutron target station of the MLF at the J-PARC at the time of the Great East Japan Earthquake (GEJE). At the date of the GEJE, in the MLF, strong quakes were detected at several instruments, an external power supply were lost, all of the circulation systems were shut down automatically, and a hydrogen gas was released as planned. Leakage of activation liquids and gases did not occur. While, the quakes made gaps between shield blocks and ruptured external pipe lines for air and water by subsidence. But significant damages on the components of the target station were not found though a loss of compressed air supply affected lock systems with air cylinders and pneumatic operation values. These results substantiated a validity of safety design on the target station for emergency accidents.
collisions at 
= 200 GeVAdare, A.*; Afanasiev, S.*; Aidala, C.*; Ajitanand, N. N.*; Akiba, Y.*; Al-Bataineh, H.*; Alexander, J.*; Aoki, K.*; Aphecetche, L.*; Armendariz, R.*; et al.
Physical Review D, 84(1), p.012006_1 - 012006_18, 2011/07
Times Cited Count：29 Percentile：73.24(Astronomy & Astrophysics)We report on the event structure and double helicity asymmetry (
) of jet production in longitudinally polarized collisions at = 200 GeV. Photons and charged particles were measured by the PHENIX experiment. Event structure was compared with the results from PYTHIA event generator. The production rate of reconstructed jets is satisfactorily reproduced with the next-to-leading-order perturbative QCD calculation. We measured = -0.0014 
0.0037 at the lowest 
bin and -0.0181 0.0282 at the highest bin. The measured is compared with the predictions that assume various 
distributions.
collisions at = 200 and 62.4 GeVAdare, A.*; Afanasiev, S.*; Aidala, C.*; Ajitanand, N. N.*; Akiba, Yasuyuki*; Al-Bataineh, H.*; Alexander, J.*; Aoki, Kazuya*; Aphecetche, L.*; Armendariz, R.*; et al.
Physical Review C, 83(6), p.064903_1 - 064903_29, 2011/06
Times Cited Count：184 Percentile：99.45(Physics, Nuclear)Transverse momentum distributions and yields for 
, and 
in collisions at = 200 and 62.4 GeV at midrapidity are measured by the PHENIX experiment at the RHIC. We present the inverse slope parameter, mean transverse momentum, and yield per unit rapidity at each energy, and compare them to other measurements at different collisions. We also present the scaling properties such as 
and 
scaling and discuss the mechanism of the particle production in collisions. The measured spectra are compared to next-to-leading order perturbative QCD calculations.
and intermediate- states in an 
=2 quantum spin chain with on-site and 
anisotropiesTonegawa, Takashi*; Okamoto, Kiyomi*; Nakano, Hiroki*; Sakai, Toru; Nomura, Kiyohide*; Kaburagi, Makoto*
Journal of the Physical Society of Japan, 80(4), p.043001_1 - 043001_4, 2011/04
Times Cited Count：37 Percentile：82.26(Physics, Multidisciplinary)Using mainly numerical method, we investigate the ground-state phase diagram of the =2 quantum spin chain with on-site and anisotropies. As a result we found a new phase between the well-known Haldane phase and the large- phase. The precise phase diagram is presented by the level spectroscopy method.
+ collisions at = 200 GeV and scaling properties of hadron productionAdare, A.*; Afanasiev, S.*; Aidala, C.*; Ajitanand, N. N.*; Akiba, Y.*; Al-Bataineh, H.*; Alexander, J.*; Aoki, K.*; Aphecetche, L.*; Armendariz, R.*; et al.
Physical Review D, 83(5), p.052004_1 - 052004_26, 2011/03
Times Cited Count：177 Percentile：98.48(Astronomy & Astrophysics)The PHENIX experiment at RHIC has measured the invariant differential cross section for production of 
, 
, 
and 
mesons in collisions at = 200 GeV. The spectral shapes of all hadron transverse momentum distributions are well described by a Tsallis distribution functional form with only two parameters, 
and 
, determining the high 
and characterizing the low regions for the spectra, respectively. The integrated invariant cross sections calculated from the fitted distributions are found to be consistent with existing measurements and with statistical model predictions.
Okamoto, Kiyomi*; Sato, Masahiro*; Okunishi, Koichi*; Sakai, Toru; Itoi, Chigaku*
Physica E, 43(3), p.769 - 772, 2011/01
Times Cited Count：5 Percentile：25.28(Nanoscience & Nanotechnology)The magnetization process of the 3-leg quantum spin nanotube is investigated by the numerical diagonalization of finite-size clusters and the density matrix renormalization group method. It is found that the magnetization plateau appears at 1/3 of the saturation magnetization for sufficiently large interchain coupling. In addition we find that in the presence of asymmetric lattice distortion, there are two different mechanisms of the magnetization plateau formation. We also successfully present a phase diagram of the magnetization plateau.
Sakai, Toru; Sato, Masahiro*; Okamoto, Kiyomi*; Okunishi, Koichi*; Itoi, Chigaku*
Journal of Physics; Condensed Matter, 22(40), p.403201_1 - 403201_13, 2010/10
Times Cited Count：36 Percentile：39.53(Physics, Condensed Matter)Recent developments of theoretical studies on spin nanotubes are reviewed, especially focusing on the S=1/2 three-leg spin tube. In contrast to the three-leg spin ladder, the tube has a spin gap in case of the regular-triangle unit cell when the rung interaction is sufficiently large. The effective theory based on the Hubbard Hamiltonian indicates a quantum phase transition to the gapless spin liquid due to the lattice distortion to an isosceles triangle. This is also supported by the numerical diagonalization and the density matrix renormalization group analyses. Furthermore, combining analytical and numerical approaches, we reveal several novel magnetic-field-induced phenomena: N
el, dimer, chiral and/or inhomogeneous orders, new mechanism for the magnetization plateau formation, and others. The recently synthesized spin tube materials are also briefly introduced.
Sakai, Toru; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*; Sato, Masahiro*
Journal of Low Temperature Physics, 159(1-2), p.55 - 59, 2010/04
Times Cited Count：8 Percentile：37.38(Physics, Applied)The numerical study on the S=1/2 three-leg spin nanotube using the exact diagonalization and the density matrix renormalization group method indicated that the 1/3 magnetization plateau appears for sufficently large rung interaction caused by two different mechanisms, depending on the asymmetry.
Tomita, Takuro*; Iwami, Masahiro*; Yamamoto, Minoru*; Deki, Manato*; Matsuo, Shigeki*; Hashimoto, Shuichi*; Nakagawa, Yoshinori*; Kitada, Takahiro*; Isu, Toshiro*; Saito, Shingo*; et al.
Materials Science Forum, 645-648, p.239 - 242, 2010/04
no abstracts in English
Sakai, Toru; Tonegawa, Takashi*; Okamoto, Kiyomi*
Physica Status Solidi (B), 247(3), p.583 - 585, 2010/03
Times Cited Count：4 Percentile：21.9(Physics, Condensed Matter)The spin ladder system with the easy-axis anisotropy in magnetic field is theoretically investigated using the numerically exact diagonalization, the density matrix renormalization group (DMRG) and the finite-size scaling analysis. It is found that the field-induced nematic phase appears above the critical field. In addition, there exists another critical field at which the quantum phase transition from the nematic phase to the conventional field-induced Tomonaga- Luttinger liquid phase occurs. The phase diagram on the coupling anisotropy versus magnetization plane is given by the numerical diagonalization. Furthermore, a typical magnetization curve calculated by the DMRG is presented.
Sakai, Toru; Okamoto, Kiyomi*; Tonegawa, Takashi*
Journal of Physics; Conference Series, 200, p.022052_1 - 022052_4, 2010/02
Times Cited Count：4 Percentile：80.32(Materials Science, Multidisciplinary)The distorted diamond chain has attracted a lot of interest, since the compound Cu
(CO)
(OH), so-called azurite, was revealed to be a good candidate for this system. Although several theoretical studies were performed, the strong anisotropy observed in the magnetization measurement of azurite has not been explained very well. To solve the mechanism of this anisotropy, we introduce the Dzyaloshinsky-Moriya (DM) interaction suitable for the crystal symmetry of azurite. The numerical diagonalization study on this realistic model indicates that the anisotropy in the experimental magnetization curve would be reproduced with sufficiently large DM interaction.
Sakai, Toru; Okamoto, Kiyomi*; Tonegawa, Takashi*
Journal of Physics; Conference Series, 150, p.042169_1 - 042169_4, 2009/03
Times Cited Count：2 Percentile：74.15(Thermodynamics)The magnetization process of the spin ladder systems with ferromagnetic rung exchange interaction is theoretically investigated using the numerical exact diagonalization and the finite-size scaling technique. It is found that with some easy-axis anisotropy the system would exhibit a new two-step spin flop transition induced by an external magnetic field.
Sakai, Toru; Okamoto, Kiyomi*; Tonegawa, Takashi*
Journal of Physics; Conference Series, 145, p.012065_1 - 012065_4, 2009/01
Times Cited Count：3 Percentile：55.52(Physics, Condensed Matter)The magnetization process of the S=1/2 distorted diamond spin chain is investigated by the numerical exact diagonalization and the finite-size scaling analysis. It is found that the system exhibits a field-induced incommensurate order close to the magnetization plateau at 1/3 of the saturation magnetization. Possible realization of the supersolid will be also discussed.
Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Otsuka, Yuichi*; Okamoto, Kiyomi*; Itoi, Chigaku*
Physical Review B, 78(18), p.184415_1 - 184415_11, 2008/11
Times Cited Count：48 Percentile：83.53(Materials Science, Multidisciplinary)We investigate quantum phase transitions of the S = 
three-leg antiferromagnetic spin tube with asymmetric inter-chain (rung) exchange interactions. On the basis of the electron tube system, we propose a useful effective theory to give the global phase diagram of the asymmetric spin tube. In addition, using other effective theories we raise the reliability of the phase diagram. The density-matrix renormalization-group and the numerical diagonalization analyses show that the finite spin gap appears in a narrow region around the rung-symmetric line.
