Ground-state phase diagram of an anisotropic S=1/2 ladder with alternating rung interactions

Tonegawa, Takashi*; Okamoto, Kiyomi*; Hikihara, Toshiya*; Sakai, Toru

Journal of Physics; Conference Series, 683(1), p.012039_1 - 012039_7, 2016/02

https://doi.org/10.1088/1742-6596/683/1/012039

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.

Annual report of Nuclear Emergency Assistance and Training Center (April 1, 2013 - March 31, 2014)

Sato, Takeshi; Muto, Shigeo; Akiyama, Kiyomitsu; Aoki, Kazufumi; Okamoto, Akiko; Kawakami, Takeshi; Kume, Nobuhide; Nakanishi, Chika; Koie, Masahiro; Kawamata, Hiroyuki; et al.

JAEA-Review 2014-048, 69 Pages, 2015/02

JAEA-Review-2014-048.pdf:13.91MB

JAEA was assigned as a designated public institution under the Disaster Countermeasures Basic Act and under the Armed Attack Situations Response Act. Based on these Acts, the JAEA has the responsibility of providing technical support to the national government and/or local governments in case of disaster responses or response in the event of a military attack, etc. In order to fulfill the tasks, the JAEA has established the Emergency Action Plan and the Civil Protection Action Plan. In case of a nuclear emergency, NEAT dispatches specialists of JAEA, supplies the national government and local governments with emergency equipment and materials, and gives technical advice and information. In normal time, NEAT provides various exercises and training courses concerning nuclear disaster prevention to those personnel taking an active part in emergency response institutions of the national and local governments, police, fire fighters, self-defense forces, etc. in addition to the JAEA itself. The NEAT also researches nuclear disaster preparedness and response, and cooperates with international organizations. In the FY2013, the NEAT accomplished the following tasks: (1) Technical support activities as a designated public institution in cooperation with the national and local governments, etc. (2) Human resource development, exercise and training of nuclear emergency response personnel for the national and local governments, etc. (3) Researches on nuclear disaster preparedness and response, and sending useful information (4) International contributions to Asian countries on nuclear disaster preparedness and response in collaboration with the international organizations

Exotic quantum phenomena of the spin nanotubes

Sakai, Toru; Okamoto, Kiyomi*

JPS Conference Proceedings (Internet), 1, p.012025_1 - 012025_4, 2014/03

https://doi.org/10.7566/JPSCP.1.012025

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.

Annual report of Nuclear Emergency Assistance and Training Center (April 1, 2012 - March 31, 2013)

Sato, Takeshi; Muto, Shigeo; Okuno, Hiroshi; Katagiri, Hiromi; Akiyama, Kiyomitsu; Okamoto, Akiko; Koie, Masahiro; Ikeda, Takeshi; Nemotochi, Toshimasa; Saito, Toru; et al.

JAEA-Review 2013-046, 65 Pages, 2014/02

JAEA-Review-2013-046.pdf:11.18MB

When a nuclear emergency occurs in Japan, the Japan Atomic Energy Agency (JAEA) has the responsibility of providing technical support to the National government, local governments, police, fire stations and nuclear operators etc., because the JAEA has been designated as the Designated Public Institution under the Basic Act on Disaster Control Measures and the Act on Response to Armed Attack Situations, etc.. The Nuclear Emergency Assistance and Training Center (NEAT) of JAEA provides a comprehensive range of technical support activities to an Off-Site Center in case of a nuclear emergency. Specifically, NEAT gives technical advice and information, dispatches specialists as required, and supplies the National Government and local governments with emergency equipments and materials. NEAT provides various exercise and training courses concerning nuclear disaster prevention to those personnel taking an active part in emergency response organizations at normal times. The tasks of NEAT, with its past experiences as a designated public institution including the responses to TEPCO's Fukushima Accident, have been shifted to technical supports to the national government for strengthening its abilities to emergency responses; the NEAT therefore focused on maintenance and operation of its functions, and strengthening its response abilities in cooperation with the national government. This annual report summarized these activities of JAEA/NEAT in the fiscal year 2012.

Magnetization plateau of the quantum spin nanotube

Okamoto, Kiyomi*; Sato, Masahiro*; Okunishi, Koichi*; Sakai, Toru; Itoi, Chigaku*

Physica E, 43(3), p.769 - 772, 2011/01

https://doi.org/10.1016/j.physe.2010.07.047

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.

Field induced exotic phenomena of the S=1/2 three-leg quantum spin nanotube

Sakai, Toru; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*; Sato, Masahiro*

Journal of Low Temperature Physics, 159(1-2), p.55 - 59, 2010/04

https://doi.org/10.1007/s10909-009-0075-9

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.

Magnetization process of the S=1/2 distorted diamond spin chain with the Dzyaloshinsky-Moriya interaction

Sakai, Toru; Okamoto, Kiyomi*; Tonegawa, Takashi*

Journal of Physics; Conference Series, 200, p.022052_1 - 022052_4, 2010/02

https://doi.org/10.1088/1742-6596/200/2/022052

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.

Field-induced incommensurate order and possible supersolid in the S=1/2 frustrated diamond chain

Sakai, Toru; Okamoto, Kiyomi*; Tonegawa, Takashi*

Journal of Physics; Conference Series, 145, p.012065_1 - 012065_4, 2009/01

https://doi.org/10.1088/1742-6596/145/1/012065

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.

One-third magnetization plateau in an anisotropic ()=(1,2) spin-alternating chain

Tonegawa, Takashi*; Sakai, Toru; Okamoto, Kiyomi*; Kaburagi, Makoto*

Journal of the Physical Society of Japan, 76(12), p.124701_1 - 124701_8, 2007/12

https://doi.org/10.1143/JPSJ.76.124701

Applying the numerical diagonalization and the density matrix renormalization for the (1,2) spin alternating chain, we found two different mechanisms of the 1/3 magnetization plateau formation depending on the anisotropy and presented the phase diagram of the mechanisms of 1/3 plateau.

Field-induced incommensurate order in frustrated spin ladder

Sakai, Toru; Okamoto, Kiyomi*

Journal of Physics; Condensed Matter, 19(14), p.145231_1 - 145231_5, 2007/04

https://doi.org/10.1088/0953-8984/19/14/145231

The =1/2 frustrated spin ladder is investigated by the numerical exact diagonalization and the finite-size scaling. It is found that if the frustration is strong enough, a possible new phase with an incommensurate long-range order would appear in magnetic field.