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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：69.93(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：69.93(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.
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：82.35(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.
Sakai, Toru; Tonegawa, Takashi*; Okamoto, Kiyomi*
Physica Status Solidi (B), 247(3), p.583 - 585, 2010/03
Times Cited Count：4 Percentile：21.96(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：80.4(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：55.61(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.
)=(1,2) spin-alternating chainTonegawa, Takashi*; Sakai, Toru; Okamoto, Kiyomi*; Kaburagi, Makoto*
Journal of the Physical Society of Japan, 76(12), p.124701_1 - 124701_8, 2007/12
Times Cited Count：6 Percentile：41.7(Physics, Multidisciplinary)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.
Sakai, Toru; Okamoto, Kiyomi*; Tonegawa, Takashi*
Physica E, 40(2), p.359 - 362, 2007/12
Times Cited Count：1 Percentile：6.7(Nanoscience & Nanotechnology)The study by the numerical diagonalization and finite-size scaling revealed that the spin 1 and 2 alternating nanowire magnet exhibits a new quantum spin flop transition between two different Tomonaga-Luttinger liquids.
Nakano, Tomohide; Fujimoto, Takashi*; Goto, Motoshi*; Hatayama, Akiyoshi*; Kado, Shinichiro*; Kato, Takako*; Kimura, Mineo*; Kubo, Hirotaka; Murakami, Izumi*; Ono, Noriyasu*; et al.
Annual Report of National Institute for Fusion Science; April 2003 - March 2004, P. 414, 2003/10
no abstracts in English
Sakai, Toru; Tonegawa, Takashi*; Okamoto, Kiyomi*
no journal, ,
The magnetization process of the S=1 and S=2 spin alternating ferrimagnetic chain with the single-ion anisotropies is investigated by the numerical exact diagonalization and the density matrix renormalization group method. It is found that the mechanism of the 2/3 magnetization plateau formation due to quantum effects depends on the anisotropy constants. The obtained phase diagram of the 2/3 plateau is revealed to include three different phases.
Sakai, Toru; Tonegawa, Takashi*; Okamoto, Kiyomi*
no journal, ,
no abstracts in English
Sakai, Toru; Okamoto, Kiyomi*; Tonegawa, Takashi*
no journal, ,
no abstracts in English
Sakai, Toru; Tonegawa, Takashi*; Okamoto, Kiyomi*
no journal, ,
no abstracts in English
Sakai, Toru; Tonegawa, Takashi*; Okamoto, Kiyomi*
no journal, ,
The S=1/2 distorted diamond chain is investigated by the density matrix renormalization group and the numerical exact diagonalization. We found that an incommensurate long-range order is induced by the external magnetic field above the 1/3 magnetization plateau. We using this result theoretically explain the field induced incommensurate order observed in the azurite.
