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Okamoto, Kiyomi*; Sato, Masahiro*; Okunishi, Koichi*; Sakai, Toru; Itoi, Chigaku*
Physica E, 43(3), p.769 - 772, 2011/01
Times Cited Count：5 Percentile：25.35(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：35 Percentile：39.2(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：37.46(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.
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：83.59(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.
Sakai, Toru; Okunishi, Koichi*; Otsuka, Yuichi*; Okamoto, Kiyomi*; Sato, Masahiro*; Itoi, Chigaku*
no journal, ,
The spin nanotube was theoretically investigated by the numerical exact diagonalization and the density matrix renormalization group method. It was found that the three-leg spin tube exhibits a quantum phase transition between the spin gap and gapless phases, as a lattice distortion occurs. The superconductivity induced by the spin gap is also discussed.
Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Otsuka, Yuichi*; Okamoto, Kiyomi*; Itoi, Chigaku*
no journal, ,
We investigate quantum phase transitions of the S=1/2 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.
Sakai, Toru; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*; Sato, Masahiro*
no journal, ,
no abstracts in English
Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*
no journal, ,
The S=1/2 three-leg spin tube has a spin gap due to the strong frustration. Using the numerical dyagonalization and the density matrix renormalization group (DMRG) calculation, we revealed new quantum phase transitions between the spin-gap and gapless phases induced by an asymmetric interchain interactions. Under high magnetic field this system also exhibits some interesting phenomena. The same numerical analysis on the magnetization process indicates that the 1/3 magnetization plateau appears for sufficiently large rung interaction caused by two different mechanisms, depending on the asymmetry.
Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*
no journal, ,
no abstracts in English
Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*
no journal, ,
Recently some quantum spin systems on tube lattices, so called spin nanotubes, have been synthesized. They are expected to be interesting low-dimensional systems like the carbon nanotubes. As the first step of theoretical study on the spin nanotube, we investigate the S=1/2 three-leg spin tube, which is the simplest one, using the density matrix renormalization group (DMRG) and the numerical exact diagonalization (ED), combined with a precise finite-size scaling analysis named level spectroscopy.
Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*
no journal, ,
Recently some quantum spin systems on tube lattices, so called spin nanotubes, have been synthesized. They are expected to be interesting low-dimensional systems like the carbon nanotubes. As the first step of theoretical study on the spin nanotube, we investigate the S=1/2 three-leg spin tube, which is the simplest one, using the density matrix renormalization group (DMRG) and the numerical exact diagonalization (ED), combined with a finite-size scaling analysis. Particularly, we introduce the lattice distortion from the regular triangle unit to the isosceles one. We revealed that the S=1/2 isosceles triangle spin tube exhibits various exotic quantum phase transitions.
Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*
no journal, ,
The spin tube has attracted a lot of interest as a magnet with a nanotube structure. Various applicable functions of the spin tube are expected to be induced by high magnetic field. The S=1/2 three-leg spin tube has a spin gap due to the strong frustration. Using the numerical dyagonalization and the density matrix renormalization group (DMRG) calculation, we revealed new quantum phase transitions between the spin-gap and gapless phases induced by an asymmetric interchain interactions. Under high magnetic field this system also exhibits some interesting phenomena. The same numerical analysis on the magnetization process indicates that the 1/3 magnetization plateau appears for sufficiently large rung interaction caused by two different mechanisms, depending on the asymmetry. A field induced symmetry breaking accompanied by the chiral order is also revealed to occur.
Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*; Nakano, Hiroki*
no journal, ,
The S=1/2 spin nanotube is theoretically investigated by the numerical diagonalization and the density matrix renormalization group. We found some new quantum phase transitions with respect to the ratio of the leg and rung exchange interactions. Some interesting quantum phenomena in the carrier doped spin tube will be also discussed.
