Quantum phase transition and magnetic excitation in the =1/2 Ising-like antiferromagnetic chain CsCoCl in transverse magnetic fields

Kimura, Shojiro*; Onishi, Hiroaki; Narumi, Yasuo*; Okunishi, Koichi*; Hagiwara, Masayuki*; Kindo, Koichi*; Kikuchi, Hikomitsu*

Journal of the Physical Society of Japan, 94(12), p.124703_1 - 124703_8, 2025/12

https://doi.org/10.7566/JPSJ.94.124703

Optical selection rules of the magnetic excitation in the = one-dimensional Ising-like antiferromagnet BaCoVO

Kimura, Shojiro*; Onishi, Hiroaki; Okutani, Akira*; Akaki, Mitsuru*; Narumi, Yasuo*; Hagiwara, Masayuki*; Okunishi, Koichi*; Kindo, Koichi*; He, Z.*; Taniyama, Tomoyasu*; et al.

Physical Review B, 105(1), p.014417_1 - 014417_9, 2022/01

https://doi.org/10.1103/PhysRevB.105.014417

Exotic quantum phase transition of the spin nanotube

Sakai, Toru; Nakano, Hiroki*; Okunishi, Koichi*

Journal of Physics; Conference Series, 568(4), p.042024_1 - 042024_5, 2014/00

https://doi.org/10.1088/1742-6596/568/4/042024

The spin nanotube is investigated by the numerical diagonalization and the level spectroscopy analysis. As a result, the quantum phase transition between the spin gap and gapless phases was revealed to occur with respect to the ratio of the rung and leg exchange interactions.

Quantum spin nanotubes; Frustration, competing orders and criticalities

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

Journal of Physics; Condensed Matter, 22(40), p.403201_1 - 403201_13, 2010/10

https://doi.org/10.1088/0953-8984/22/40/403201

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: Nel, 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.

Quantum phase transitions of the asymmetric three-leg spin tube

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

Physical Review B, 78(18), p.184415_1 - 184415_11, 2008/11

https://doi.org/10.1103/PhysRevB.78.184415

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.

Quantum phase transition of the S=1/2 three-leg spin tube

Sakai, Toru; Kasahara, Toshihiro*; Nakano, Hiroki*; Hijii, Keigo*; Okunishi, Koichi*; Okamoto, Kiyomi*

no journal, , 

We report the result from the theoretical study based on the numerical diagonalization and the finite-size scaling analysis, on the quantum phase transition which occurs when the ratio of the rung coupling, the leg coupling and the ring exchange interactions is varied, in the S=1/2 three-leg spin tube.

Quantum phase transitions of the spin nanotubes

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.

Quantum phase transition of the S=1/2 three-leg spin tube

Sakai, Toru; Nakano, Hiroki*; Okunishi, Koichi*

no journal, , 

The S=1/2 three-leg spin tube is investigated using the large-scale numerical diagonalization up to 42 spins and the level spectroscopy method. The critical ratio of the rung and leg exchange interactions where a quantum phase transition occurs between the gapless and gapped phases is estimated precisely.

Quantum phase transitions of the three-leg spin tub

Sakai, Toru; Okunishi, Koichi*; Okamoto, Kiyomi*

no journal, , 

The S=1/2 three-leg quantum spin tube is one of strongly frustrated low-dimensional magnets. Using the numerical diagonalization and the DMRG calculation, we revealed new quantum phase transitions induced by an asymmetric interchain interactions. We also found some anomalous field-induced phenomena; the magnetization plateau, cusp, and chiral order in spin liquid phases.

Spin nanotubes

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.