研究業績
  1. "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)

  2. "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)

  3. "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)

  4. "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)

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

  6. "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)

  7. "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)

  8. "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)

  9. "Wilson-like real-space renormalization group and low-energy effective spectrum of the XXZ chain in the critical regime"
    Kouichi Okunishi
    cond-mat/0702581; to appear in JPSJ.

  10. "Filling-dependence of the zigzag Hubbard ladder for a quasi-one-dimensional superconductor Pr_2Ba_4Cu_7O_{15-delta} "
    Kouichi Okunishi
    cond-mat/0610734 to appear in PRB.

  11. "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)

  12. "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)

  13. "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)

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

  15. "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)

  16. "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)

  17. "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)

  18. "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)

  19. "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

  20. "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)

  21. "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)

  22. "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)

  23. "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)

  24. "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)

  25. "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)

  26. "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)

  27. "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)
     
  28. "Two-Dimensional Tensor Product Variational Formulation"
    T. Nishino, Y. Hieida, K. Okunishi, N. Maeshima and Y. Akutsu.
    Prog. Theor. Phys. 105, 409-417 (2001) (cond-mat/0011103)
     
  29. "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)
     
  30. "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
     
  31. "Antiferromagnetic Zigzag Spin Chain in Magnetic Fileds at finite temperatures"
    Nobuya Maeshima and Kouichi Okunishi
    Phys. Rev. B 62 (2000) 934-939
     
  32. 論文，『Kramers-Wannier Approxmation for 3D Ising model』，共著，
    Prog. Theor. Phys.103：541-548 (2000).
    奥西巧一，西野友年
  33. 論文，『Middle-Field Cusp Singularities in the Magnetization Process of One-Dimensional Quantum Antiferromagnets』, 共著，
    Phys. Rev. B 60, R6953-R6956 (1999).
    奥西巧一，日永田泰啓，阿久津泰弘
  34. 論文，『Transfer Matrix Approach to Classical Systems』, 共著，
    Springer Lecture Note in Physics 528, Springer, Berlin (1999).
    西野友年，奥西巧一，引原俊也，その他,
  35. 論文，『Magnetization Curve of Bilinear-Biquadratic Spin Chain at Finite Temperature』，単著，
    Phys. Rev. B 60, 4043-4050 (1999).
    奥西巧一
  36. 論文，『Corner Transfer Matrix Algorithm for Classical Renormalization group』，共著，
    J.Phys.Soc.Jpn. 66, 3040 (1997).
    西野友年，奥西巧一
  37. 論文，『Universal relation between the dispersion curve and the ground-state correlation length in 1D antiferromagnetic quantum spin systems』共著，
    Phys. Rev. B 64, 104432 (2001).
    K. Okunishi, Y. Akutsu, N. Akutsu and T. Yamamoto