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Kusano, Kanya*; Ichimoto, Kiyoshi*; Ishii, Mamoru*; Miyoshi, Yoshizumi*; Yoden, Shigeo*; Akiyoshi, Hideharu*; Asai, Ayumi*; Ebihara, Yusuke*; Fujiwara, Hitoshi*; Goto, Tadanori*; et al.
Earth, Planets and Space (Internet), 73(1), p.159_1 - 159_29, 2021/12
Times Cited Count：6 Percentile：49.29(Geosciences, Multidisciplinary)The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.
Al and determination of the effective proton charge in the sd-shellDe Rydt, M.*; Neyens, G.*; Asahi, Koichiro*; Balabanski, D. L.*; Daugas, J. M.*; Depuydt, M.*; Gaudefroy, L.*; Gr
vy, S.*; Hasama, Yuka*; Ichikawa, Yuichi*; et al.
Physics Letters B, 678(4), p.344 - 349, 2009/07
Times Cited Count：17 Percentile：69.88(Astronomy & Astrophysics)no abstracts in English
Otsuka, Yuichi*; Seo, Hitoshi; Motome, Yukitoshi*; Kato, Takeo*
Physica B; Condensed Matter, 404(3-4), p.479 - 481, 2009/03
Times Cited Count：5 Percentile：25.54(Physics, Condensed Matter)We investigate ground state properties of a quasi-one-dimensional electron-lattice coupled model for quarter-filled molecular conductors. The effective one-dimensional extended Hubbard model coupled to adiabatic lattice degree of freedom is derived by the inter-chain mean-field approximation and solved by Lanczos exact diagonalization method. We find that the critical behavior among lattice tetramerized states with different charge-lattice ordered patterns is sensitively affected by the inter-chain Coulomb interaction, lattice anharmonicity, and intrinsic dimerization.
Otsuka, Yuichi*; Seo, Hitoshi; Motome, Yukitoshi*; Kato, Takeo*
Journal of the Physical Society of Japan, 77(11), p.113705_1 - 113705_4, 2008/11
Times Cited Count：30 Percentile：77.48(Physics, Multidisciplinary)Finite-temperature phase transitions in quasi-one-dimensional quarter-filled systems are investigated using the extended Hubbard model with electron-lattice coupling. By a quantum Monte Carlo method combined with interchain mean-field approximation, we clarify competing and coexisting behaviors among charge ordering, dimer Mott, and spin-Peierls states. The results are compared with experimental data for quasi-one-dimensional molecular conductors such as DCNQI and TMTTF compounds.
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：83.53(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.
Seo, Hitoshi; Yoshioka, Hideo*; Otsuka, Yuichi*
Journal of Physics; Conference Series, 132, p.012018_1 - 012018_6, 2008/00
We theoretically investigate the possibility of a Mott insulating state in a class of molecular conductors where the composition ratio between two molecular species is incommensurate to each other, i.e., incommensurate molecular conductors. Although the band-filling becomes irrational and then metallic behavior would be expected, the on-site Coulomb repulsion among the valence electrons together with the potential from the closed-shellions supplying the carriers can give rise to an "incommensurate Mott insulator", which is characterized by the carriers being localized with a period incommensurate to the underlying lattice.
nucleus 
CrOnishi, Takeo*; Gelberg, A.*; Sakurai, Hiroyoshi*; Yoneda, Kenichiro*; Aoi, Nori*; Imai, Nobuaki*; Baba, Hidetada*; Von Brentano, P.*; Fukuda, Naoki*; Ichikawa, Yuichi*; et al.
Physical Review C, 72(2), p.024308_1 - 024308_7, 2005/08
Times Cited Count：21 Percentile：77.62(Physics, Nuclear)no abstracts in English
Hirata, Yuichi*; Onishi, Akira*; Nara, Yasushi*; Kido, Toshihiko; Maruyama, Toshiki; Otsuka, Naohiko*; Niita, Koji*; Takada, Hiroshi; Chiba, Satoshi
Nuclear Physics A, 707(1-2), p.193 - 212, 2002/08
Times Cited Count：10 Percentile：51.1(Physics, Nuclear)no abstracts in English
Sakai, Toru; Sato, Masahiro; Otsuka, Yuichi*; Okunishi, Koichi*; Okamoto, Kiyomi*
no journal, ,
The S=1/2 three-leg frustrated antiferromagnetic spin tube is investigated using the numerical diagonalization, density matrix renormalization group, and effective field theory techniques. Varing one of the three rung couplings, a quantum phase transition between the spin gap and gapless phases was predicted in our previous work. The present phenomenological renormalization approach gives a phase diagram of the spin gap. In addition we study the magnetization process of the regular triangle spin tube. Our present effective field theory between the lower critical field where the spin gap vanishes, and the upper critical field where the magnetization is saturated, predicts two field-induced new phases appear; the one has the vector chiral order and the other has an inhomogeneous distribution of the magnetization. These two phases coexist with the Tomonaga-Luttinger liquid phase. The prediction is confirmed by the numerical diagonalization and finite-size scaling analyses.
Sakai, Toru; Otsuka, Yuichi*; Sato, Masahiro*; Okunishi, Koichi*; Okamoto, Kiyomi*
no journal, ,
The magnetization process of the 3-leg spin tube is investigated by some numerical simulations and field-theoretical approaches. As a result, we successfully predict the quantum phase transitions at which the 1/3 magnetization plateau appears, and at which the chiral order occurs. More quantitative analyses on these quantum phase transitions give the critical points and lead to a proposal of some new experiments to discover them.
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.
