publication list

Original Papers

  1. "Translational symmetry broken magnetization plateau of the S=1 antiferromagnetic Heisenberg chain with competing anisotropies"
    Toru Sakai, Kiyomi Okamoto, Kouichi Okunishi, Masaru Hashimoto, Tomoki Houda, Rito Furuchi, Hiroki Nakano
    Phys. Rev. B 108, 174435 (2023)(8 pages) (arXiv:2311.07123)

  2. "Statistical Mechanics Approach to the Holographic Renormalization Group: Bethe Lattice Ising Model and p-adic AdS/CFT"
    Kouichi Okunishi, Tadashi Takayanagi
    Prog. Theor. Exp. Phys. 013A03 (2024) (24 pages) (arXiv:2310.12601)
    Typos: in Eq.(9), (p-1) should be (p+1) ; in Eq. (11), arctan should be arctanh

  3. "A new technique to incorporate multiple fermion flavors in tensor renormalization group method for lattice gauge theories"
    Atis Yosprakob, Jun Nishimura, Kouichi Okunishi
    JHEP 11, 187 (2023) (31 pages) (arXiv:2309.01422)

  4. "Magnetic Excitation in the S = 1/2 Ising-like Antiferromagnetic Chain CsCoCl3 in Longitudinal Magnetic Fields Studied by High-field ESR Measurements"
    Shojiro Kimura, Hiroaki Onishi, Kouichi Okunishi, Mitsuru Akaki, Yasuo Narumi, Masayuki Hagiwara, Koichi Kindo, and Hikomitsu Kikuchi
    J. Phys. Soc. Jpn. 92, 094701 (2023) (9 Pages)

  5. "Entanglement bipartitioning and tree tensor networks"
    Kouichi Okunishi, Hiroshi Ueda, Tomotoshi Nishino
    Prog. Theor. Exp. Phys. 023A02 (2023) (14 pages) ( arXiv:2210.11741) .

  6. "Automatic structural optimization of tree tensor networks"
    Toshiya Hikihara, Hiroshi Ueda, Kouichi Okunishi, Kenji Harada, Tomotoshi Nishino
    Phys. Rev. Research 5, 013031 (2023) (11 pages) ( arXiv:2209.03196 )

  7. "Angular-time evolution for the Affleck-Kennedy-Lieb-Tasaki chain and its edge-state dynamics"
    Koutaro Nakajima, Kouichi Okunishi
    Phys. Rev. B 106, 134304 (2022) (9 pages), (arXiv:2205.06428).

  8. "Duality, Criticality, Anomaly, and Topology in Quantum Spin-1 Chains"
    Hong Yang, Linhao Li, Kouichi Okunishi, Hosho Katsura
    Phys. Rev. B 107, 125158 (2023), (14 pages) (arXiv:2203.15791)

  9. "Optical selection rules of the magnetic excitation in the S=12 one-dimensional Ising-like antiferromagnet BaCo2V2O8"
    S. Kimura, H. Onishi, A. Okutani, M. Akaki, Y. Narumi, M. Hagiwara, K. Okunishi, K. Kindo, Z. He, T. Taniyama, and M. Itoh
    Phys. Rev. B 105, 014417 (2022) (9 pages)

  10. "Entanglement-based tensor-network strong-disorder renormalization group"
    Kouichi Seki, Toshiya Hikihara, Kouichi Okunishi
    Phys. RevB. 104 134405 (2021) (9 pages), (arXiv:2107.01555 )

  11. "Tensor-network strong-disorder renormalization groups for random quantum spin systems in two dimensions"
    Kouichi Seki, Toshiya Hikihara, Kouichi Okunishi
    Phys. Rev. B 102, 144439 (2020) (10 pages) (arXiv:2006.12857)

  12. "Corner transfer matrix renormalization group analysis of the two-dimensional dodecahedron model"
    Hiroshi Ueda, Kouichi Okunishi, Seiji Yunoki, Tomotoshi Nishino
    Phys. Rev. E 102, 032130 (2020) (8 pages), (arXiv:2004.08669)

  13. "Finite-m scaling analysis of Berezinskii-Kosterlitz-Thouless phase transitions and entanglement spectrum for the six-state clock model
    Hiroshi Ueda, Kouichi Okunishi, Kenji Harada, Roman Krcmar, Andrej Gendiar, Seiji Yunoki, Tomotoshi Nishino
    Phys. Rev. E 101, 062111 (2020) (7 pages), (arXiv:2001.10176)

  14. "Lattice Unruh effect and world-line entanglement for the XXZ chain"
    Kouichi Okunishi and Kouichi Seki
    J. Phys. Soc. Jpn. 88, 114002 (2019) (8 pages) (arXiv:1906.10441)

  15. "Magnetism and high-magnetic field magnetization in alkali superoxide CsO2"
    M. Miyajima, F. Astuti, T. Kakuto, A. Matsuo, D. P. Sari, R. Asih, K. Okunishi, T. Nakano, Y. Nozue, K. Kindo, I. Watanabe, T. Kambe
    J. Phys. Soc. Jpn. 87, 063704 (2018) (5 pages) (arXiv:1804.00377)

  16. "Phase Transitions for Cuboc Orders in Stacked Kagome Heisenberg Systems"
    Kouichi Seki and Kouichi Okunishi
    J. Phys. Soc. Jpn. 87, 023001 (2018) (5 pages) (arXiv:1710.06174 )

  17. " Critical behavior of the two-dimensional icosahedron model"
    Hiroshi Ueda, Kouichi Okunishi, Roman Krcmar, Andrej Gendiar, Seiji Yunoki, Tomotoshi Nishino
    Phys. Rev. E 96, 062112 (2017)(6 pages) (arXiv:1709.01275)

  18. "Magnetic structure and dispersion relation of the S=1/2 quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8 in a transverse magnetic field"
    M. Matsuda, H. Onishi, A. Okutani, J. Ma, H. Agrawal, T. Hong, D. M. Pajerowski, J. R. D. Copley, K. Okunishi, M. Mori, S. Kimura, and M. Hagiwara
    Phys. Rev. B 96, 024439 (2017) (8 pages)

  19. "Snapshot spectra in the world-line quantum Monte Carlo for one-dimensional quantum spin systems"
    Kouichi Seki and Kouichi Okunishi
    J. Phys. Soc. Jpn. 88, 024003 (2019) (10 pages)(arXiv:1706.09257)

  20. "Spin-wave analysis for Kagome-triangular spin system and coupled spin tubes: low-energy excitation for the cuboc order"
    Masahiro Ochiai, Kouichi Seki and Kouichi Okunishi
    J. Phys. Soc. Jpn. 86, 114701 (2017) (8 pages) (arXiv:1706.02879)

  21. "Sine-square deformation and Mobius quantization of two-dimensional conformal field theory"
    Kouichi Okunishi
    Prog. Theor. Exp. Phys. (2016) 063A02 (14 pages) (arXiv:1603.09543)

  22. "Sine-square deformation and supersymmetric quantum mechanics"
    Kouichi Okunishi and Hosho Katsura
    J. Phys. A: Math. Theor. 48 (2015) 445208 (16 pages) (arXiv:1505.07904)
    Selected as a cover picture!

  23. "Magnetic phase diagram of the coupled triangular spin tubes for CsCrF4"
    Kouichi Seki and Kouichi Okunishi
    Phys. Rev. B 91224403 (2015)(9 pages) (arXiv:1502.06702)

  24. "Haldane State Formed by Oxygen Molecules Encapsulated in Single-Walled Carbon Nanotubes"
    Masayuki Hagiwara, Masami Ikeda, Takanori Kida, Kazuyuki Matsuda, Shin Tadera, Haruka Kyakuno, Kazuhiro Yanagi, Yutaka Maniwa, and Kouichi Okunishi
    J. Phys. Soc. Jpn. 83, 113706 (2014) (4 pages)

  25. "Field-induced incommensurate phase in the strong-rung spin ladder with ferromagnetic legs"
    H. Yamaguchi, H. Miyagai, M. Yoshida, M. Takigawa, K. Iwase, T. Ono, N. Kase, K. Araki, S. Kittaka, T. Sakakibara, T. Shimokawa, T. Okubo, K. Okunishi, A. Matsuo, and Y. Hosokoshi
    Phys. Rev. B 89, 220402(R) (2014) (5 pages) (arXiv:1406.2231)

  26. "Snapshot spectrum and critical phenomenon for two-dimensional classical spin systems"
    Yukinari Imura, Tsuyoshi Okubo, Satoshi Morita, Kouichi Okunishi
    J. Phys. Soc. Jpn. 83, 114002 (2014) (arXiv:1402.6767) (8 pages)

  27. "Fine-Tuning of Magnetic Interactions in Organic Spin Ladders"
    Hironori Yamaguchi, Hirotsugu Miyagai, Tokuro Shimokawa, Kenji Iwase, Toshio Ono, Yohei Kono, Naoki Kase, Koji Araki, Shunichiro Kittaka, Toshiro Sakakibara, Takashi Kawakami, Kouichi Okunishi, Yuko Hosokoshi
    J. Phys. Soc. Jpn. 83 (2014) 033707 (arXiv:1402.2743) (4 pages)

  28. "Symmetry-protected topological order and negative-sign problem for SO(N) bilinear-biquadratic chains"
    Kouichi Okunishi and Kenji Harada
    Phys. Rev. B 89 134422 (2014) (arXiv:1312.2643) (11 pages).

  29. "Doubling of Entanglement Spectrum in Tensor Renormalization Group"
    Hiroshi Ueda, Kouichi Okunishi, Tomotoshi Nishino
    Phys. Rev. B 89, 075116 (2014) (arXiv:1306.6829) (10 pages)

  30. "Collapse of Magnetic Order of the Quasi One-Dimensional Ising-Like Antiferromagnet BaCo2V2O8 in Transverse Fields"
    Shojiro Kimura, Koichi Okunishi, Masayuki Hagiwara, Koichi Kindo, Zhangzhen He, Tomoyasu Taniyama, Mitsuru Itoh, Keiichi Koyama, and Kazuo Watanabe
    J. Phys. Soc. Jpn. 82 (2013) 033706 (4 pages)

  31. "Magnetic Field-Induced Phase Transitions in the S=1/2 Two-Leg Spin-Ladder Material Cu(DEP)Br2"
    Zentaro Honda, Hiroko Aruga Katori, Masami Ikeda, Masayuki Hagiwara, Kouichi Okunishi, Masamichi Sakai, Takeshi Fukuda, and Norihiko Kamata
    J. Phys. Soc. Jpn. 81 (2012) 113710 (4 pages)

  32. "Wilson's numerical renormalization group and AdS_3 geometry"
    Kouichi Okunishi
    arXiv:1208.1645

  33. "Spin-Chirality Separation and S_3-Symmetry Breakings in the Magnetization Plateau of the Quantum Spin Tube"
    Kouichi Okunishi, Masahiro Sato, Toru Sakai, Kiyomi Okamoto, and Chigak Itoi
    Phys. Rev. B 85, 054416 (2012) (arXive:1109.0063) (6 pages)

  34. "Novel Phase Transition Probed by Sound Velocity in Quasi-One-Dimensional Ising-Like Antiferromagnet BaCo2V2O8"
    Hironori Yamaguchi, Shadi Yasin, Sergei Zherlitsyn, Kumiko Omura, Shojiro Kimura, Shunsuke Yoshii, Kouichi Okunishi, Zhangzhen He, Tomoyasu Taniyama, Mitsuru Itoh, and Masayuki Hagiwara
    J. Phys. Soc. Jpn. 80 (2011) 033701 (4 pages)

  35. "Topological disentangler for the valence-bond-solid chain"
    Kouichi Okunishi
    Phys. Rev. B 83, 104411 (2011) (arXiv:1011.3277) (4 pages)

  36. "Uniform Matrix Product State in the Thermodynamic Limit"
    Hiroshi Ueda, Isao Maruyama, Kouichi Okunishi
    J. Phys. Soc. Jpn. 80, 023001 (2011) (4 pages) (arXiv:1011.0576)

  37. "Scale free property and edge state of Wilson's numerical renormalization group"
    Kouichi Okunishi and Tomotoshi Nishino
    Phys. Rev. B 82 144409 (2010) (arXiv:1001.2594)(7 pages)

  38. "High-Field Magnetism of the Spin-Ladder Material Na2Fe2(C2O4)3(H2O)2"
    Hironori Yamaguchi, Shojiro Kimura, Zentaro Honda, Kouichi Okunishi, Synge Todo, Koichi Kindo, and Masayuki Hagiwara
    J. Phys. Soc. Jpn. 78 (2009) 124701 (5 pages)

  39. "Magnetic Field versus Temperature Phase Diagram of the Spin-1/2 Alternating-Bond Chain Compound F5PNN"
    Yasuo Yoshida, Tatsuya Kawae, Yuko Hosokoshi, Katsuya Inoue, Nobuya Maeshima, Kouichi Okunishi, Kiyomi Okamoto, and Toru Sakai
    J. Phys. Soc. Jpn. 78 (2009) 074716 (5 pages) (arXiv:0711.2336)

  40. "Wang-Landau simulation for the quasi-one-dimensional Ising model"
    Takayuki Tanabe and Kouichi Okunishi
    J. Phys. Soc. Jpn. 78 054002 (2009) (arXiv:0901.0637)
  41. "Longitudinal SDW order in a quasi-1D Ising-like quantum antiferromagnet"
    S. Kimura, M. Matsuda, T. Masuda, S. Hondo, K. Kaneko, N. Metoki, M. Hagiwara, T. Takeuchi, K. Okunishi, Z. He, K. Kindo, T. Taniyama, M. Itoh
    Phys. Rev. Lett. 101, 207201 (2008)(arXiv:0808.4073)

  42. "Quantum phase transitions of the asymmetric three-leg spin tube"
    Toru Sakai, Masahiro Sato, Kouichi Okunishi, Yuichi Otsuka, Kiyomi Okamoto, Chigak Itoi
    Phys. Rev. B 78, 184415 (2008)(arXiv:0807.4769)

  43. "On calculation of vector spin chirality for zigzag spin chains"
    Kouichi Okunishi
    J. Phys. Soc. Jpn. 77, (2008) 114004 (arXiv:0805.3872)

  44. "Exotic Finite-Temperature Phase Diagram for Weakly Coupled S = 1/2 XXZ Chain in a Magnetic Field"
    Takahumi Suzuki, Naoki Kawashima and Kouichi Okunishi
    J. Phys. Soc. Jpn. 76, (2007) 123707 (4 pages)

  45. "Field-induced incommensurate order for the quasi-one-dimensional XXZ model in a magnetic field"
    Kouichi Okunishi and Takahumi Suzuki
    Phys. Rev. B 76 224411 (2007) (5 pages)(cond-mat/0708.0264)

  46. "Novel ordering of an S = 1/2 quasi one-dimensional Ising-like anitiferromagnet in magnetic field"
    S. Kimura, T. Takeuchi, K. Okunishi, M. Hagiwara, Z. He, K. Kindo, T. Taniyama, M. Itoh
    Phys. Rev. Lett. 100, 057202 (2008) (cond-mat/0707.3713)

  47. "Field induced order-disorder transition driven by a softening of spinon excitation"
    S. Kimura, H. Yashiro, K. Okunishi, M. Hagiwara, Z. He, K. Kindo, T. Taniyama, M. Itoh
    Phys. Rev. Lett. 99, 087602 (2007)

  48. "Wilson-like real-space renormalization group and low-energy effective spectrum of the XXZ chain in the critical regime"
    Kouichi Okunishi
    J. Phys. Soc. Jpn. 76 063001 (2007) (cond-mat/0702581)

  49. "Filling dependence of the zigzag Hubbard ladder for the quasi-one-dimensional superconductor Pr_2Ba_4Cu_7O_{15-delta} "
    Kouichi Okunishi
    Phys. Rev. B 75, 174514 (2007) (cond-mat/0610734)

  50. "Possibility of field-induced incommensurate order in a quasi-one-dimensional frustrated spin system"
    N. Maeshima, K. Okunishi, K. Okamoto, T. Sakai and K. Yonemitsu
    J. Phys.: condens. matt.18, (2006) 4819-4826 (cond-mat/0604194)

  51. "Field-induced Berezinskii-Kosterlitz-Thouless Transition and String-Density Plateau in Anisotropic Triangular Antiferromagnetic Ising Model"
    Hiromi Otsuka, Yutaka Okabe, and Kouichi Okunishi
    Phys. Rev. E 73, 035105(R) (2006) (4 pages)(cond-mat/0510653)

  52. "Product Wave Function Renormalization Group: construction from the matrix product point of view"
    Kouji Ueda, Tomotoshi Nishino, Kouichi Okunishi, Yasuhiro Hieida, Rene Derian, Andrej Gendiar
    J. Phys. Soc. Jpn. 75,014003 (2006) (cond-mat/0509320)

  53. "Real-space renormalization group approach for the corner Hamiltonian"
    Kouichi Okunishi
    J. Phys. Soc. Jpn. 74 3186 (2005) (cond-mat/0507195)

  54. "Frustration induced eta inversion in the S=1/2 bond alternating spin chain"
    Nobuya Maeshima, Kouichi Okunishi, Kiyomi Okamoto and Toru Sakai
    Phys. Rev. Lett. 93, 127203 (2004) (cond-mat/0403349)

  55. "Quantum Fluctuation-induced Phase Transition in S=1/2 XY-like Heisenberg Antiferromagnets on the Triangular Lattice"
    Shin-ichiro Yoshikawa, Kouichi Okunishi, Makoto Senda and Seiji Miyashita.
    J. Phys. Soc. jpn. 73, 1798-1804 (2004)(cond-mat/0403335)

  56. "High-field magnetization of $S = 1$ antiferromagnetic bond-alternating chain compounds"
    Yasuo Narumi, Koichi Kindo, Masayuki Hagiwara, Hiroki Nakano, Akira Kawaguchi, Kouichi Okunishi and Masanori Kohno.
    Phys. Rev. B 69, 174405 (2004) (7 pages)

  57. "Fractional S^z excitation and its bound state around the 1/3 plateau of the Ising-like zigzag XXZ chain"
    K. Okunishi and T. Tonegawa.
    Phy. Rev. B 68, 224422 (2003) (cond-mat/0307121)

  58. "Exchange Interaction via Crystal-Field Excited States and Its Importance in CsCoCl3"
    Hiroyuki Shiba, Yoshifumi Ueda, Kouichi Okunishi, Shojiro Kimura and Koichi Kindo
    J. Phys. Soc. Jpn. 72 (2003) 2326-2333

  59. "Magnetic phase diagram of the S=1/2 antiferromagnetic zigzag spin chain in the strongly frustrated region: cusp and plateau"
    Kouichi Okunishi and Takashi Tonegawa.
    J. Phys. Soc. Jpn. 72, 479-482 (2003) (cond-mat/0211458)

  60. "Magnetic properties of a S=1/2 zigzag spin compound (N_2H_5)CuCl_3"
    N. Maeshima, M. Hagiwara, Y. Narumi, K. Kindo, T.C. Kobayashi and K. Okunishi.
    J. Phys.:condens.matter.15 3607-3618 (2003) (cond-mat/0208373)

  61. "Hole-doping effects on a frustrated spin ladder"
    Akira Kawaguchi, Akihisa Koga, Kouichi Okunishi and Norio Kawakami.
    J. Phys. Soc. Jpn. 72 405-410 (2003) (cond-mat/0205635)

  62. "Magnetization process for a quasi-one-dimensional S=1 antiferromagnet"
    Akira Kawaguchi, Akihisa Koga, Kouichi Okunishi and Norio Kawakami.
    Phys. Rev. B 65 214405 (2002) (cond-mat/0202080)

  63. "Spinon excitation and Mobius boundary condition in S=1/2 antiferromagnetic Heisenberg spin ladder with zigzag structure"
    Kouichi Okunishi and Nobuya Maeshima.
    Phys. Rev. B 64, 212406 (2001) (cond-mat/0104101)

  64. "Anisotropic antiferromagnetic spin chains in a transverse field: reentrant behavior of the staggered magnetization"
    Y. Hieida, K. Okunishi and Y. Akutsu
    Phys. Rev. B 64, 224422 (2001) (cond-mat/0103371)

  65. "Vertical density matrix algorithm: A higher dimensiinal numerical renormalization scheme based on the tensor product state ansats"
    N. Maeshima, Y. Hieida, Y. Akutsu, T. Nishino and K. Okunishi
    Phys. Rev. E 64, 016705 (2001). (cond-mat/0101360)

  66. "Universal relation between the dispersion curve and the ground-state correlation length in 1D antiferromagnetic quantum spin systems"
    K. Okunishi, Y. Akutsu, N. Akutsu and T. Yamamoto
    Phys. Rev. B 64, 104432 (2001). (cond-mat/0107021)

  67. "Two-Dimensional Tensor Product Variational Formulation"
    T. Nishino, Y. Hieida, K. Okunishi, N. Maeshima, Y. Akutsu and A. Gendiar.
    Prog. Theor. Phys. 105, 409-417 (2001) (cond-mat/0011103)

  68. "First-order quantum phase transition in the orthogonal-dimer spin chain"
    A. Koga, K. Okunishi and N. Kawakami
    Phys. Rev. B 62, 5558-5563 (2000)

  69. "Self-Consistent Tensor Product Variational Approxmation for 3D Classical models"
    T. Nishino, K. Okunishi, N. Maeshima, Y. Hieida and Y. Akutsu.
    Nucl. Phys. B 575 [FS](2000) 504-512

  70. "Antiferromagnetic Zigzag Spin Chain in Magnetic Fileds at finite temperatures"
    Nobuya Maeshima and Kouichi Okunishi
    Phys. Rev. B 62 (2000) 934-939

  71. "Kramers-Wannier Approxmation for 3D Ising model"
    K. Okunishi and T. Nishino
    Prog. Theor. Phys. 103 , (2000) 541-548.

  72. "Middle-Field Cusp Singularities in the Magnetization Process of One-Dimensional Quantum Antiferromagnets"
    K. Okunishi, Y. Hieida and Y. Akutsu
    Phys. Rev. B 60, (1999) R6953.

  73. "Numerical Renormalization Approach to Two-Dimensional Quantum Antiferromagnets with Valence-Bond-Solid Type Ground State"
    Y. Hieida, K. Okunishi and Y. Akutsu
    New. J. Phys. 1(1999) 7.

  74. "Universal Asymptotic Eigenvalue Distribution of Density Matrices and Corner Transfer Matrices in the Thermodynamic Linit"
    Kouichi Okunishi, Yasuhiro Hieida and Yasuhiro Akutsu.
    Phys. Rev. E 59, (1999) R6227.
     
  75. "Magnetization Curve of Bilinear-Biquadratic Spin Chain at Finite Temperature"
    K. Okunishi
    Phys. Rev. B 60, (1999) 4043.
     
  76. "A Densiry Matrix Algorithm for 3D Classical Models"
    T. Nishino and K. Okunishi
    J. Phys. Soc. Jpn.67 (1998) 3066

  77. "Delta-Function Bose Gas Picture of S=1 Antiferromagnetic Spin Chain Near Critical Field"
    K. Okunishi, Y. Hieida and Y. Akutsu.
    Phys. Rev. B 59 (1999) 6806
     
  78. "Numerical Latent Heat Observation of the q=5 Potts Model"
    T. Nishino and K. Okunishi,
    J. Phys. Soc. Jp. 67 (1998) 1492, (short note).

  79. "Corner Transfer Matrix Algorithm for Classical Renormalization Groups"
    T. Nishino and K. Okunishi,
    J. Phys. Soc. Jp. 66 (1997) 3040 .

  80. "Magnetization Process of One-Dimensional Quantum Antiferromagnet:Product Wavefunction Renormarization Group Approach"
    Yasuhiro Hieida, Kouichi Okunishi and Yasuhiro Akutsu,
    Phys. Lett. A 233 (1997) 464

  81. "Corner Transfer Matrix Renormalization Group Method"
    T. Nishino and K. Okunishi,
    J. Phys. Soc. Jp. 65 (1996) 891.

  82. "Renormarization Group at Criticality"
    T. Nishino, K. Okunishi and M. Kikuchi,
    Phys. Lett. A 213 (1996) 69.

  83. "Product WaveFunction Renormarization Group Method"
    T. Nishino and K. Okunishi,
    J. Phys. Soc. Jp. 64 (1995) 4084.

Review Articles

  1. "Developments in the Tensor Network --- from Statistical Mechanics to Quantum Entanglement"
    Kouichi Okunishi, Tomotoshi Nishino, Hiroshi Ueda
    J. Phys. Soc. Jpn. 91, 062001 (2022) (arxiv:2111.12223)

  2. "Unconventional magnetic excitations and spin dynamics of exotic quantum spin systems BaCo_2 V_2 O_8 and Ba_3CuSb_2O_9"
    Yibo Han, Shojiro Kimura, Kouichi Okunishi and Masayuki Hagiwara
    Applied Magnetic Resonance, (2020) 1-14

  3. "Quantum spin nanotubes -- frustration, competing orders and criticalities"
    Toru Sakai, Masahiro Sato, Kouichi Okunishi, Kiyomi Okamoto, Chigak Itoi
    J. Phys.: Condens. Matter 22 (2010) 403201 (arXiv:1007.5102)

  4. "Transfer Matrix Approach to Classical Systems"
    T. Nishino and K. Okunishi, T. Hikihara, and H. Takasaki
    Springer Lecture Note in Physics 528. eds. I. Peschel, X. Wang, K. Halberg
    Springer, Berlin (1999).

  5. "Density Matrix Renormalization Group" (Review)
    --- Introduction from a variational view point ---
    T.Nishino, T.Hikihara, K.Okunishi , and Y.Hieida
    Int. J. Mod. Phys. B 13, (1999) 1
     
  6. "Density Matrix Renormalization for Classical Lattice Models"
    T. Nishino and K. Okunishi
    in "Strongly Correlated Magnetic and Superconducting Systems" Springer Lecture Note in Physics 478.
    eds. G.Sierra and M.A. Martin-Delgado (1997) 167.
    　　

Proceedings

  1. "Visualization of Entanglement Geometry by Structural Optimization of Tree Tensor Network"
    Toshiya Hikihara, Hiroshi Ueda, Kouichi Okunishi, Kenji Harada, Tomotoshi Nishino
    arXiv:2401.16000 (9 pages)

  2. "Translational Symmetry Broken Magnetization Plateau of the Spin-1/2 Ferromagnetic and Antiferromagnetic Bond-Alternating Spin Chain with Competing Anisotropies"
    T Sakai, M Hashimoto, T Houda, R Furuchi, H Nakano, K Okamoto, K. Okunishi
    New Physics: Sae Mulli 73, 1131 (2023) (4 pages)

  3. "Magnetic Properties of One- and Two-Dimensional Functional Materials: Oxygen Molecules Encapsulated in Single-Walled Carbon Nanotubes and Copper Ions Embedded into Phthalocyanine Sheets"
    Masayuki Hagiwara, Takanori Kida, Kazuyuki Matsuda, Haruka Kyakuno, Yutaka Maniwa, Zentaro Honda, Yuya Sakaguchi, Makoto Tashiro, Masamichi Sakai, Takeshi Fukuda, Norihiko Kamata, Kouichi Okunishi
    Open Chemistry Journal 6 27-33 (2019)

  4. "A low-energy effective model for the S=1/2 Kagome-triangular-strip Heisenberg model"
    K. Okunishi, Y. Onozato, K. Seki,
    ICM2018, AIP advances 8, 101401 (2018).

  5. "Numerical Study of Random Correlation Matrices: Finite Size Effects"
    Y. Arai, K. Okunishi and H. Iyetomi,
    Intelligent Decision Technologies, SIST 10(2011), pp.557-565

  6. " Half magnetization plateau of a frustrated S = 1 antiferromagnetic chain"
    T Tonegawa , H Nakano , T Sakai , K Okamoto , K Okunishi and K Nomura
    J. Phys.: Conf. Ser. 200 022065 2010.

  7. "Wang-Landau simulation of the quasi-one-dimensional spin systems"
    Kouichi Okunishi and Takayuki Tanabe
    J. Phys.: Conf. Ser. 200 022043 2010

  8. "Exotic incommensurate order of weakly coupled S=1/2 XXZ antiferromagnetic chains"
    Takafumi Suzuki , Naoki Kawashima and Kouichi Okunishi
    J. Phys.: Conf. Ser. 150 042197 2009

  9. "Energy gap of spin nanotube"
    Toru Sakai, Munehisa Matsumoto, Kouichi Okunishi, Kiyomi Okamoto, Masahiro Sato
    Physica E: Low-dimensional Systems and Nanostructures, Volume 29, Issues 3-4, November 2005, Pages 633-636

  10. "High field magnetism of the quasi one-dimensional anisotropic antiferromagnet BaCo2V2O8"
    S. Kimura, H. Yashiro, M. Hagiwara, K. Okunishi, K. Kindo, Z. He, T. Taniyama and M. Itoh,
    RHFM, Sendai.
    J. Phys. Conference series 51 99 (2006)

  11. "Phase diagram and string-density plateau state of the anisotropic triangular anntiferromagnetic Ising model"
    Hiromi Otsuka, Yutaka Okabe and Kouichi Okunishi
    HFM2006 proceedings
    J. Phys. Condens. Matter. 19 (2007) 145236(6pp).

  12. "Chemical potential-electron density curve of the zigzag Hubbard ladder for Pr 247"
    Kouichi Okunishi
    ICM2006 kyoto proceedings
    J. Mag. Mag. Mat. 310(2007) 1108-1109.

  13. "Finite-field ground state of an S=1 zigzag ladder"
    T. Tonegawa, K. Okamoto, K. Okunishi, T. Sakai
    ICM2006 kyoto proceedings
    J. Mag. Mag. Mat. 310(2007) e372-e374.

  14. "Quantum Phase Transition in the Three-leg Spin Nanotube"
    T. Sakai, K. Okunishi, K. Okamoto, M. Sato, M. Matsumoto, Y. Otsuka
    ICM2006 kyoto proceedings
    J. Mag. Mag. Mat. 310 (2007) e423-e425.

  15. "Finite-Field Ground State of an S = 1 Anisotropic Antiferromagnetic Chain"
    T.Sakai, M.Matsumoto, K.Okunishi, K.Okamoto and M.Sato
    Physica E 29, 633 (2005)

  16. "Finite-Field Ground State of an S = 1 Anisotropic Antiferromagnetic Chain"
    Takashi Tonegawa, Kouichi Okunishi, ToruSakai and Makoto Kaburagi
    Prog. Theor. Phys. Suppl. 159 77-81 (2005)

  17. "Effect of Staggered Field on the Magnetization Process of S = 1/2 Antiferromagnetic Chains"
    Akira Matsuo, Kohei Hosokawa, Yasuo Narumi, Kouichi Okunishi, Nobuya Maeshima, Takayuki Asano, Yoshitami Ajiro, Naoyuki Ishida, Takashi Nogami and Koichi Kindo
    Prog. Theor. Phys. Suppl. 159 158-162 (2005)

  18. "Magnetization Plateau of S = 1 Spin Ladder BIP-TENO"
    Munehisa Kikuchi, Kiyomi Okamoto, Kouichi Okunishi and Toru Sakai
    Prog. Theor. Phys. Suppl. 159,251-255 (2005)

  19. "Low-Energy Excitations of the S = 1/2 Quantum Spin Tube with the Triangular Lattice Structure"
    Kouichi Okunishi, Shin-ichiro Yoshikawa, ToruSakai and Seiji Miyashita
    Prog. Theor. Phys. Suppl. 159, 297-301 (2005)

  20. "Fractional Sz excitation and its bound state for the S=1/2 antiferromagnetic zigzag spin chain in a magnetic field""
    SPQS, date:2004/7/17-20; place: Sendai, Japan.
    J. Phys. Soc. Jpn. Suppl. 74 151-156 (2005) (cond-mat/0505719)
    K. Okunishi and T. Tonegawa

  21. "Field-Induced Phase Transitions and Long-Range Orders in the S=1/2 Spin Bond-Alternating Chain with Frustrating Interaction"
    SPQS, date:2004/7/17-20; place: Sendai, Japan.
    J. Phys. Soc. Jpn. Suppl. 74 63-66 (2005)
    Nobuya Maeshima, Kouichi Okunishi, Kiyomi Okamoto, Toru Sakai, and Kenji Yonemitsu

  22. "Magnetization plateaux in an S=1/2 antiferromagnetic chain with frustration and bond-alternation "
    T. Tonegawa, K. Okamoto, K.Okunishi, K.Nomura and M. Kaburagi.
    Physica B 346-347 (2004) 50-54

  23. "Magnetization plateau and cusp in S=1 spin ladder"
    T. Sakai, K. Okamoto, K.Okunishi, K. Kindo, Y.Narumi, Y.Hosokoshi, K.Katoh, K. Inoue and T.Goto.
    Physica B 346-347 (2004) 34-47

  24. "The magnetization process of an Ising-type frustrated S = 1 spin chain"
    M Kaburagi, M Kang, T Tonegawa and K Okunishi
    J. Phys.:Condens. Matter 16 (2004) S765-S772 Conference paper (HighlyFrustrated Magnetism 2003, 26-30th August 2003, Grenoble, France)

  25. "Anomalous magnetization process in frustrated spin ladders"
    Toru Sakai, Kiyomi Okamoto, Kouichi Okunishi, and Masahiro Sato
    J. Phys.:Condens. Matter 16 (2004) S785-S789(cond-mat/0308473) Conference paper (HighlyFrustrated Magnetism 2003, 26-30th August 2003, Grenoble, France)

  26. "Hole-Doping Effects on Orthogonal-Dimer Spin Chain"
    ISSP-Kashiwa 2001 Correlated Electrons, date: 2001/10/2-5; Place: ISSP, University of Tokyo, Kashiwa, Chiba, Japan.
    J. Phys. Chem. Solid. 63 (2002) 1431-1434.
    A. Kawaguchi, A. Koga, K. Okunishi and N. Kawakami.

  27. "Magnetization curves of qusi-one dimensional Haldane systems"
    Physical Phenomena at High Magnetic Fields IV, date:2001/10/19-25; place: Sweeney Convention Center, Santa Fe, New Mexico, USA.
    Physical Phenomena at High Magnetic Fields IV, 447-450, World Scientific (2002)
    A. Kawaguchi, A. Koga, K. Okunishi and N. Kawakami.

  28. "First-order phase transition in frustrated spin systems"
    Order diorder in quantum spin systems, date:2001/11/15-16; place: Kyoto-kaikan, Kyoto, Japan.
    Prog. Theor. Phys. Suppl. 145 , (2002) 52-58.
    A. Kawaguchi, A. Koga, K. Okunishi and N. Kawakami.

  29. "The cusp singurality in the magnetization curve of the 1D quantum spin chains"(invited)
    Order diorder in quantum spin systems, date:2001/11/15-16; place: Kyoto-kaikan, Kyoto, Japan.
    Prog. Theor. Phys. Suppl. 145 , (2002) 119-124.
    K. Okunishi

  30. "Matrix product state approximation for the maximum-eigenvalue eigenstate of the quantum transfer matrix"
    Order diorder in quantum spin systems, date:2001/11/15-16; place: Kyoto-kaikan, Kyoto, Japan.
    Prog. Theor. Phys. Suppl. 145 , (2002) 204-208.
    N. Maeshima, Y. Hieida, T. Nishino and K. Okunishi

  31. "High-field magnetization of a S=1/2 zigzag chain compound (N2H5)CuCl3"
    M. Hagiwara, Y. Narumi, K. Kindo, N. Maeshima, K. Okunishi, T. Sakai, M. Takahashi.
    Physica B 294-295 (2001) 83-86
     

Japanese

  1. "量子多体系とテンソルネットワーク 〜表現形式の普遍性〜"
    奥西巧一　数理科学　2022年1月号.

  2. "「密度行列繰り込み群」の変分原理"
    西野友年、 奥西巧一、 引原俊哉、 物性研究 68‐2 (1997-5).

  3. "密度行列繰り込み群"
    西野友年、日永田泰啓、奥西巧一、日本物理学会誌 No.10 (2000)763-771.