110 citations · 859 across the 63 of their papers we have counts for
13 papers · 1 filter
Exact ground states of frustrated quantum spin systems consisting of spin-dimer units
Toshiya Hikihara, Takashi Tonegawa, Kiyomi Okamoto +1
We study frustrated quantum spin systems consisting of dimers of spin-1/2 spins. We derive several models that have the exact ground state of the form of the direct product of dime…
How to distinguish the Haldane/Large-D state and the intermediate-D state in an S=2 quantum spin chain with the XXZ and on-site anisotropies
Kiyomi Okamoto, Takashi Tonegawa, Hiroki Nakano +3
We numerically investigate the ground-state phase diagram of an S=2 quantum spin chain with the and on-site anisotropies described by ${\mathcal H}=\sum_j (S_j^x S_{j+1}^x+S_…
Quantum spin nanotubes -- frustration, competing orders and criticalities
Toru Sakai, Masahiro Sato, Kouichi Okunishi +2
Recent developments of theoretical studies on spin nanotubes are reviewed, especially focusing on the three-leg spin tube. In contrast to the three-leg spin ladder, the tub…
Inversion phenomenon and phase diagram of the distorted diamond chain with the interaction anisotropy
Akiyuki Tokuno, Kiyomi Okamoto
We discuss the anisotropies of the Hamiltonian and the wave-function in an distorted diamond chain. The ground-state phase diagram of this model is investigated using the d…
Finite-Field Ground State of the S=1 Antiferromagnetic-Ferromagnetic Bond-Alternating Chain
Takashi Tonegawa, Kiyomi Okamoto, Makoto Kaburagi
We investigate the finite-field ground state of the S=1 antiferromagnetic-ferromagnetic bond-alternating chain described by the Hamiltonian ${\calH}=\sum\nolimits_{\ell}\bigl\{\vec…
Quantum magnetization plateaux of an anisotropic ferrimagnetic spin chain
Toru Sakai, Kiyomi Okamoto
The magnetization curve of the ferrimagnetic alternating spin chain with the single-ion anisotropy is investigated with the numerical exact diagonalization of f…
Level Spectroscopy: Physical Meaning and Application to the Magnetization Plateau Problems
Kiyomi Okamoto
We review the level spectroscopy, which is a powerful method of analyzing the numerical data with respect to the Berezinskii-Kosterlitz-Thouless quantum phase transition in one dim…
Anisotropies of the Hamiltonian and the Wave Function: Inversion Phenomena in Quantum Spin Chains
Kiyomi Okamoto
We investigate the inversion phenomenon between the XXZ anisotropies of the Hamiltonian and the wave function in quantum spin chains, mainly focusing on the S=1/2 trimerized XXZ mo…
Inversion Phenomena of the Anisotropies of the Hamiltonian and the Wave-Function in the Distorted Diamond Type Spin Chain
Kiyomi Okamoto, Yutaka Ichikawa
We investigate the ground-sate phase diagram of the XXZ version of the S=1/2 distorted diamond chain by use of the degenerate perturbation theory near the truncation point. In case…
Magnetization-plateau state of the S=3/2 spin chain with single ion anisotropy
Atsuhiro Kitazawa, Kiyomi Okamoto
We reexamine the numerical study of the magnetized state of the S=3/2 spin chain with single ion anisotropy D(> 0) for the magnetization M=M_{S}/3, where M_{S} is the saturation ma…
Breakdown of the magnetization plateau of the S=1/2 ferromagnetic-ferromagnetic-antiferromagnetic trimerized spin chain with anisotropy
Atsuhiro Kitazawa, Kiyomi Okamoto
We study the breakdown of the magnetization plateau at the magnetization M=M_{S}/3 (M_{S} is the saturation magnetization) of the S=1/2 anisotropic spin chain with ferromagnetic-fe…
Quantum Phase Transition of S=1/2 Trimerized XXZ Spin Chain in Magnetic Field
Kiyomi Okamoto, Atsuhiro Kitazawa
We study the magnetization plateau at a third of the saturation magnetization of the S=1/2 trimerized XXZ spin chain at T=0. The appearance of the plateau depends on the values of…
Magnetization plateau and quantum phase transition of the S=1/2 trimerized XXZ spin chain
Kiyomi Okamoto, Atsuhiro Kitazawa
We study the plateau of the magnetization curve at ( is the saturation magnetization) of the trimerized spin chain. By examining the leve…