Papers
  • Topological Nernst effect emerging from real-space gauge field and thermal fluctuations in a magnetic skyrmion lattice
    H. Oike, T. Ebino, Takashi Koretsune, A. Kikkawa, M. Hirschberger, Y. Taguchi, Y. Tokura, and F. Kagawa
    Phys. Rev. B 106 214425 (2022)
  • sparse-ir: Optimal compression and sparse sampling of many-body propagators
    Markus Wallerberger, Samuel Badr, Shintaro Hoshino, Sebastian Huber, Fumiya Kakizawa, Takashi Koretsune, Yuki Nagai, Kosuke Nogaki, Takuya Nomoto, Hitoshi Mori, Junya Otsuki, Soshun Ozaki, Thomas Plaikner, Rihito Sakurai, Constanze Vogel, Niklas Witt, Kazuyoshi Yoshimi, Hiroshi Shinaoka
    Software X 21 101266 (2023)
  • Optimal alloying in hydrides: Reaching room-temperature superconductivity in LaH10
    Tianchun Wang, José A. Flores-Livas, Takuya Nomoto, Yanming Ma, Takashi Koretsune, and Ryotaro Arita
    Phys. Rev. B 105 174516 (2022)
  • Wannier-based implementation of the coherent potential approximation with applications to Fe-based transition metal alloys
    Naohiro Ito, Takuya Nomoto, Koji Kobayashi, Sergiy Mankovsky, Kentaro Nomura, Ryotaro Arita, Hubert Ebert, and T. Koretsune
    Phys. Rev. B 105 125136 (2022)
  • Large anomalous Nernst effect and nodal plane in an iron-based kagome ferromagnet
    T. Chen, S. Minami, A. Sakai, Y. Wang, Z. Feng, T. Nomoto, M. Hirayama, R. Ishi, T. Koretsune, R. Arita, and S. Nakatsuji
    Science Advances 8 (2022)
  • Magneto-optical spectroscopy on Weyl nodes for anomalous and topological Hall effects in chiral MnGe
    Y. Hayashi, Y. Okamura, N. Kanazawa, T. Yu, T. Koretsune, R. Arita, A. Tsukazaki, M. Ichikawa, M. Kawasaki, Y. Tokura and Y. Takahashi
    Nature Communications 12 5974 (2021)
  • X-ray study of ferroic octupole order producing anomalous Hall effect
    Motoi Kimata, Norimasa Sasabe, Kensuke Kurita, Yuichi Yamasaki, Chihiro Tabata, Yuichi Yokoyama, Yoshinori Kotani, Muhammad Ikhlas, Takahiro Tomita, Kenta Amemiya, Hiroyuki Nojiri, Satoru Nakatsuji, Takashi Koretsune, Hironori Nakao, Taka-hisa Arima, and Tetsuya Nakamura
    Nature Communications 12 5582 (2021)
  • Absence of conventional room-temperature superconductivity at high pressure in carbon-doped H3S
    Tianchun Wang, Motoaki Hirayama, Takuya Nomoto, Takashi Koretsune, Ryotaro Arita, and José A. Flores-Livas
    Phys. Rev. B 104 064510 (2021)
  • Effect of symmetry breaking on short-wavelength acoustic phonons in the chiral magnet MnSi
    Y. Nii, Y. Hirokane, T. Koretsune, D. Ishikawa, A. Q. R. Baron, and Y. Onose
    Phys. Rev. B 104 L081101 (2021)
  • Quantum anomalous Hall effect in a three-dimensional topological-insulator–thin-film-ferromagnetic-metal heterostructure
    Katsuhiro Arimoto, Takashi Koretsune, Kentaro Nomura
    Phys. Rev. B 103 235315 (2021)
  • Anomalous transport due to Weyl fermions in the chiral antiferromagnets Mn3X, X = Sn, Ge
    Taishi Chen, Takahiro Tomita, Susumu Minami, Mingxuan Fu, Takashi Koretsune, Motoharu Kitatani, Ikhlas Muhammad, Daisuke Nishio-Hamane, Rieko Ishii, Fumiyuki Ishii, Ryotaro Arita and Satoru Nakatsuji
    Nature Comm. 12 572 (2021)
  • Geometrical Hall effect and momentum-space Berry curvature from spin-reversed band pairs
    Max Hirschberger, Yusuke Nomura, Hiroyuki Mitamura, Atsushi Miyake, Takashi Koretsune, Yoshio Kaneko, Leonie Spitz, Yasujiro Taguchi, Akira Matsuo, Koichi Kindo, Ryotaro Arita, Masashi Tokunaga, and Yoshinori Tokura
    Phys. Rev. B 103 L041111 (2021)
  • Enhancement of the transverse thermoelectric conductivity originating from stationary points in nodal lines
    Susumu Minami, Fumiyuki Ishii, Motoaki Hirayama, Takuya Nomoto, T. Koretsune, and Ryotaro Arita
    Phys. Rev. B 102 205128 (2020)
  • Efficient ab initio Migdal-Eliashberg calculation considering the retardation effect in phonon-mediated superconductors
    Tianchun Wang, Takuya Nomoto, Yusuke Nomura, Hiroshi Shinaoka, Junya Otsuki, T. Koretsune, and Ryotaro Arita
    Phys. Rev. B 102 134503 (2020)
  • Giant magneto-optical responses in magnetic Weyl semimetal Co3Sn2S2
    Y. Okamura, S. Minami, Y. Kato, Y. Fujishiro, Y. Kaneko, J. Ikeda, J. Muramoto, R. Kaneko, K. Ueda, V. Kocsis, N. Kanazawa, Y. Taguchi, T. Koretsune, K. Fujiwara, A. Tsukazaki, R. Arita, Y. Tokura, and Y. Takahashi
    Nature Communications 11 4619 (2020)
  • Topological Kagome magnet Co3Sn2S2 thin flakes with high electron mobility and large anomalous Hall effect
    Miuko Tanaka, Yukako Fujishiro, Masataka Mogi, Yoshio Kaneko, Takamoto Yokosawa, Naoya Kanazawa, Susumu Minami, Takashi Koretsune, Ryotaro Arita, Seigo Tarucha, Michihisa Yamamoto, and Yoshinori Tokura
    Nano Lett. 20 7476 (2020)
  • Formation mechanism of helical Q structure in Gd-based skyrmion materials
    Takuya Nomoto, Takashi Koretsune, and Ryotaro Arita
    Phys. Rev. Lett. 125 117204 (2020)
  • Local force method for the ab initio tight-binding model: Effect of spin-dependent hopping on exchange interactions
    Takuya Nomoto, Takashi Koretsune, and Ryotaro Arita
    Phys. Rev. B 102 014444 (2020)
  • Systematic first-principles study of the on-site spin-orbit coupling in crystals
    Kensuke Kurita, Takashi Koretsune
    Phys. Rev. B 102 045109 (2020)
  • Iron-based binary ferromagnets for transverse thermoelectric conversion
    Akito Sakai, Susumu Minami, Takashi Koretsune, Taishi Chen, Tomoya Higo, Yangming Wang, Takuya Nomoto, Motoaki Hirayama, Shinji Miwa, Daisuke Nishio-Hamane, Fumiyuki Ishii, Ryotaro Arita and Satoru Nakatsuji
    Nature 581 53-57 (2020)
    Press release
  • Quantum crystal structure in the 250-kelvin superconducting lanthanum hydride
    Ion Errea, Francesco Belli, Lorenzo Monacelli, Antonio Sanna, Takashi Koretsune, Terumasa Tadano, Raffaello Bianco, Matteo Calandra, Ryotaro Arita, Francesco Mauri and Jose A. Flores-Livas
    Nature 578 66-69 (2020)
    Press release
  • Wannier90 as a community code: new features and applications
    Giovanni Pizzi, Valerio Vitale, Ryotaro Arita, Stefan Bluegel, Frank Freimuth, Guillaume Géranton, Marco Gibertini, Dominik Gresch, Charles Johnson, Takashi Koretsune, Julen Ibanez, Hyungjun Lee, Jae-Mo Lihm, Daniel Marchand, Antimo Marrazzo, Yuriy Mokrousov, Jamal Ibrahim Mustafa, Yoshiro Nohara, Yusuke Nomura, Lorenzo Paulatto, Samuel Ponce, Thomas Ponweiser, Junfeng Qiao, Florian Thöle, Stepan S. Tsirkin, Malgorzata Wierzbowska, Nicola Marzari, David Vanderbilt, Ivo Souza, Arash A Mostofi and Jonathan R Yates
    Journal of Physics: Condensed Matter 32 165902 (2020)
  • Microscopic characterization of the superconducting gap function in Sn1-xInxTe
    T. Nomoto, M. Kawamura, T. Koretsune, R. Arita, T. Machida, T. Hanaguri, M. Kriener, Y. Taguchi, and Y. Tokura
    Phys. Rev. B 101 014505 (2020)
  • Ferromagnetic state above room temperature in a proximitized topological Dirac semimetal
    Masaki Uchida, Takashi Koretsune, Shin Sato, Markus Kriener, Yusuke Nakazawa, Shinichi Nishihaya, Yasujiro Taguchi, Ryotaro Arita, and Masashi Kawasaki
    Phys. Rev. B 100 245148 (2019)
  • Realization of interlayer ferromagnetic interaction in MnSb2Te4 toward the magnetic Weyl semimetal state
    Taito Murakami, Yusuke Nambu, Takashi Koretsune, Gu Xiangyu, Takafumi Yamamoto, Craig M. Brown, and Hiroshi Kageyama
    Phys. Rev. B 100 195103 (2019)
  • Topological transitions among skyrmion- and hedgehog-lattice states in cubic chiral magnets
    Y. Fujishiro, N. Kanazawa, T. Nakajima, X. Z. Yu, K. Ohishi, Y. Kawamura, K. Kakurai, T. Arima, H. Mitamura, A. Miyake, K. Akiba, M. Tokunaga, A. Matsuo, K. Kindo, T. Koretsune, R. Arita and Y. Tokura
    Nature Communications 10 1059 (2019)
    Press release
  • Finite phenine nanotubes with periodic vacancy defects
    Zhe Sun, Koki Ikemoto, Toshiya M. Fukunaga, Takashi Koretsune, Ryotaro Arita, Sota Sato, Hiroyuki Isobe
    Science 363 151 (2019)
    Press release
  • Negative-pressure-induced helimagnetism in ferromagnetic cubic perovskites Sr1-xBaxCoO3
    H. Sakai, S. Yokoyama, A. Kuwabara, J. S. White, E. Canevet, H. M. Ronnow, T. Koretsune, R. Arita, A. Miyake, M. Tokunaga, Y. Tokura, and S. Ishiwata
    Phys. Rev. Materials 2 104412 (2018)
    Press release
  • Controlling the helicity of magnetic skyrmions in a beta-Mn-type high-temperature chiral magnet
    K. Karube, K. Shibata, J. S. White, T. Koretsune, X. Z. Yu, Y. Tokunaga, H. M. Rønnow, R. Arita, T. Arima, Y. Tokura, and Y. Taguchi
    Phys. Rev. B 98 155120 (2018)
  • Maximally Localized Wannier Orbitals and the Extended Hubbard Model for Twisted Bilayer Graphene
    Mikito Koshino, Noah F. Q. Yuan, Takashi Koretsune, Masayuki Ochi, Kazuhiko Kuroki, and Liang Fu
    Phys. Rev. X 8 031087 (2018)
  • Superconductivity in Anti-ThCr2Si2-type Er2O2Bi Induced by Incorporation of Excess Oxygen with CaO Oxidant
    K. Terakado, R. Sei, H. Kawasoko, T. Koretsune, D. Oka, T. Hasegawa, and T. Fukumura
    Inorganic Chemistry 57 10587 (2018)
  • Giant anomalous Nernst effect and quantum-critical scaling in a ferromagnetic semimetal
    Akito Sakai, Yo Pierre Mizuta, Agustinus Agung Nugroho, Rombang Sihombing, Takashi Koretsune, Michi-To Suzuki, Nayuta Takemori, Rieko Ishii, Daisuke Nishio-Hamane, Ryotaro Arita, Pallab Goswami and Satoru Nakatsuji
    Nature Physics 14 1119 (2018)
    Press release
  • Electronic Structure Calculation and Superconductivity in λ-(BETS)2GaCl4
    Hirohito Aizawa, Takashi Koretsune, Kazuhiko Kuroki, and Hitoshi Seo
    J. Phys. Soc. Jpn. 87 093701 (2018)
  • Anisotropic band splitting in monolayer NbSe2: implications for superconductivity and charge density wave
    Yuki Nakata, Katsuaki Sugawara, Satoru Ichinokura, Yoshinori Okada, Taro Hitosugi, Takashi Koretsune, Keiji Ueno, Shuji Hasegawa, Takashi Takahashi and Takafumi Sato
    npj 2D Materials and Applications 2 12 (2018)
  • Tailoring band structure and band filling in a simple cubic (IV, III)-VI superconductor
    M. Kriener, M. Kamitani, T. Koretsune, R. Arita, Y. Taguchi, and Y. Tokura
    Phys. Rev. Materials 2 044802 (2018)
  • Charge-transfer complexes based on C2v-symmetric benzo[ghi]perylene: comparison of their dynamic and electronic properties with those of D6h-symmetric coronene
    Yukihiro Yoshida, Shunsuke Tango, Kazuhide Isomura, Yuto Nakamura, Hideo Kishida, Takashi Koretsune, Masafumi Sakata, Yoshiaki Nakano, Hideki Yamochiag and Gunzi Saito
    Materials Chemistry Frontiers 2 1165 (2018)
  • Large magneto-thermopower in MnGe with topological spin texture
    Y. Fujishiro, N. Kanazawa, T. Shimojima, A. Nakamura, K. Ishizaka, T. Koretsune, R. Arita, A. Miyake, H. Mitamura, K. Akiba, M. Tokunaga, J. Shiogai, S. Kimura, S. Awaji, A. Tsukazaki, A. Kikkawa, Y. Taguchi and Y. Tokura
    Nature Communications 9 408 (2018)
    Press release
  • Large magneto-optical Kerr effect and imaging of magnetic octupole domains in an antiferromagnetic metal
    Tomoya Higo, Huiyuan Man, Daniel B. Gopman, Liang Wu, Takashi Koretsune, Olaf M. J. van't Erve, Yury P. Kabanov, Dylan Rees, Yufan Li, Michi-To Suzuki, Shreyas Patankar, Muhammad Ikhlas, C. L. Chien, Ryotaro Arita, Robert D. Shull, Joseph Orenstein, and Satoru Nakatsuji
    Nature Photonics 12 73-78 (2018)
    Press release
  • First-Principles Evaluation of the Dzyaloshinskii-Moriya Interaction
    T. Koretsune, T. Kikuchi and R. Arita
    J. Phys. Soc. Jpn. 87 041011 (2018)
  • Evidence for magnetic Weyl fermions in a correlated metal
    K. Kuroda, T. Tomita, M.-T. Suzuki, C. Bareille, A. A. Nugroho, P. Goswami, M. Ochi, M. Ikhlas, M. Nakayama, S. Akebi, R. Noguchi, R. Ishii, N. Inami, K. Ono, H. Kumigashira, A. Varykhalov, T. Muro, T. Koretsune, R. Arita, S. Shin, Takeshi Kondo and S. Nakatsuji
    Nature Materials 16 1090-1095 (2017)
    Press release
  • Efficient method to calculate the electron-phonon coupling constant and superconducting transition temperature
    T. Koretsune and R. Arita
    Comp. Phys. Comm. 220C 239 (2017)
  • Large anomalous Nernst e ect at room temperature in a chiral antiferromagnet
    Muhammad Ikhlas, Takahiro Tomita, Takashi Koretsune, Michi-To Suzuki, Daisuke Nishio-Hamane, Ryotaro Arita, Yoshichika Otani and Satoru Nakatsuji
    Nature Physics 13 1085-1090 (2017)
    Press release
  • Pentagon-Embedded Cycloarylenes with Cylindrical Shapes
    Shunpei Hitosugi, Sota Sato, Taisuke Matsuno, Takashi Koretsune, Ryotaro Arita, Hiroyuki Isobe
    Angewandte Chemie 56 9106-9110 (2017)
  • Weak phonon-mediated pairing in BiS2 superconductor from first principles
    C. Morice, R. Akashi, T. Koretsune, S. S. Saxena and R. Arita
    Phys. Rev. B 95 180505(R) (2017)
  • π-electron S=1/2 quantum spin-liquid state in an ionic polyaromatic hydrocarbon
    Y. Takabayashi, M. Menelaou, H. Tamura, N. Takemori, T. Koretsune, A. Stefancic, G. Klupp, A. J. C. Buurma, Y. Nomura, R. Arita, D. Arcon, M. J. Rosseinsky and P. Kosmas
    Nature Chemistry 9 635-643 (2017)
  • Cluster multipole theory for anomalous Hall effect in antiferromagnets
    M.-T. Suzuki, T. Koretsune, M. Ochi, and R. Arita
    Phys. Rev. B 95 094406 (2017)
  • Efficient blue electroluminescence from a single-layer organic device composed solely of hydrocarbons
    T. Izumi, T. Yi, K. Ikemoto, A. Yoshii, T. Koretsune, R. Arita, H. Kita, H. Taka, S. Sato and H. Isobe
    Chem. Asian J 12 730-733 (2017)
  • Structural Modulation of Macrocyclic Materials for Charge Carrier Transport Layers in Organic Light-Emitting Devices
    A. Yoshii, K. Ikemoto, T. Izumi, H. Kita, H. Taka, T. Koretsune, R. Arita, S. Sato and H. Isobe
    ECS Journal of Solid State Science and Technology 6 M3065 (2017)
  • Nonempirical Calculation of Superconducting Transition Temperatures in Light-Element Superconductors
    R. Arita, T. Koretsune, S. Sakai, R. Akashi, Y. Nomura, W. Sano
    Advanced Materials (2017)
  • Cationic pi-Stacking Columns of Coronene Molecules with Fully Charged and Charge-Disproportionated States
    Y. Yoshida, K. Isomura, M. Maesato, T. Koretsune, Y. Nakano, H. Yamochi, M. Kishida, and G. Saito
    Cryst. Growth Des. 16 5994 (2016)
  • Gate-Tuned Thermoelectric Power in Black Phosphorus
    Y. Saito, T. Iizuka, T. Koretsune, R. Arita, S. Shimizu, and Y. Iwasa
    Nano Letter 16 4819 (2016)
  • Dzyaloshinskii-Moriya Interaction as a Consequence of a Doppler Shift due to Spin-Orbit-Induced Intrinsic Spin Current
    T. Kikuchi, T. Koretsune, R. Arita, and G. Tatara
    Phys. Rev. Lett 116 247201 (2016)
    Press release
  • Two-dimensional metallic NbS2: growth, optical identification and transport properties
    S. Zhao, T. Hotta, T. Koretsune, K. Watanabe, T. Taniguchi, K. Sugawara, T. Takahashi, H. Shinohara, R. Kitaura
    2D Materials 3 025027 (2016)
  • Effect of Van Hove singularities on high-Tc superconductivity in H3S
    W. Sano, T. Koretsune, T. Tadano, R. Akashi, and R. Arita
    Phys. Rev. B 93 094525 (2016)
  • Conducting pi Columns of Highly Symmetric Coronene, The Smallest Fragment of Graphene
    Y. Yoshida, K. Isomura, H. Kishida, Y. Kumagai, M. Mizuno, M. Sakata, T. Koretsune, Y. Nakano, H. Yamochi, M. Maesato, and G. Saito
    Chemistry A European Journal 22 6023 (2016)
  • Aromatic hydrocarbon macrocycles for highly efficient organic light-emitting devices with single-layer architectures
    Jing Yang Xue, Tomoo Izumi, Asami Yoshii, Koki Ikemoto,Takashi Koretsune, Ryosuke Akashi, Ryotaro Arita, Hideo Taka, Hiroshi Kita, Sota Sato and Hiroyuki Isobe
    Chemical Science 7 896-904 (2016)
  • In-plane electric polarization of bilayer graphene nanoribbons induced by an interlayer bias voltage
    R. Okugawa, J. Tanaka, T. Koretsune, S. Saito, and S. Murakami
    Phys. Rev. Lett. 115 156601 (2015)
  • Control of Dzyaloshinskii-Moriya interaction in Mn1-xFexGe: a first-principles study
    T. Koretsune, N. Nagaosa, and R. Arita
    Scientific Reports 5 13302 (2015)
  • Field-direction control of the type of charge carriers in nonsymmorphic IrO2
    M. Uchida, W. Sano, K. S. Takahashi, T. Koretsune, Y. Kozuka, R. Arita, Y. Tokura, and M. Kawasaki
    Phys. Rev. B 91 241119(R) (2015)
  • Spin-disordered quantum phases in a quasi-one-dimensional triangular lattice
    Yukihiro Yoshida, Hiroshi Ito, Mitsuhiko Maesato, Yasuhiro Shimizu, Hiromi Hayama, Takaaki Hiramatsu, Yuto Nakamura, Hideo Kishida, Takashi Koretsune, Chisa Hotta and Gunzi Saito
    Nature Physics 11 679 - 683 (2015)
  • Large surface relaxation in the organic semiconductor tetracene
    Hazuki Morisaki, Takashi Koretsune, Chisa Hotta, Jun Takeya, Tsuyoshi Kimura and Yusuke Wakabayashi
    Nature Communications 5 5400 (2014)
    Press release
  • Evaluating model parameters of the kappa- and beta'-type Mott insulating organic solids
    T. Koretsune and C. Hotta
    Phys. Rev. B 89 045102 (2014)
    We elucidate the model parameters for a series of organic crystals called κ- and β'-type salts by constructing the maximally localized Wannier orbitals which reproduce the bulk energy band of the first-principles methods based on the density functional theory (DFT). These materials host a dimer Mott insulator, localizing one hole per dimerized ET molecules due to strong on-dimer interaction, Ud. For all these materials, we evaluate the parameters of the two representative effective lattice models in units of molecule and on dimer, and clarify two issues. First, the conventional relationships between the two models called "dimer approximation" does not hold. Second, contrary to the previous semiempirical estimates, the degree of dimerization (which approximates Ud) does not depend much on materials, and that the overall ground state properties are controlled by the degree of anisotropy of the triangular lattice, denoted as |tc/ta| in units of dimers. We update the DFT estimates |tc/ta| of κ-ET2Cu2(CN)3, showing that it falls on a class of regular triangle with the strongest degree of frustration.
  • Isotope composition dependence of band gap energy in diamond
    H. Watanabe, T. Koretsune, S. Nakashima, S. Saito and S. Shikata
    Phys. Rev. B 88 (2013) 205420
    We present experimental results on the band-gap energies of homoepitaxial diamond films with isotopic compositions ranging from nearly pure carbon-12 (12C) to nearly pure carbon-13 (13C). Diamond crystals were grown by microwave plasma-assisted chemical vapor deposition, which controls the isotope composition and minimizes the density of impurities and defects. We find that the isotope substitution of 12C by 13C increases the band-gap energy in diamond by up to 15.4 meV at 79 K. The increase at room temperature is estimated from the temperature dependence of the band-gap renormalization due to electron-phonon interaction and is found to be even larger than that at low temperatures. These results unambiguously demonstrate the possibility of band-gap engineering of diamond via control of the isotopic composition.
  • Magneto-orbital effect without spin-orbit interactions in a noncentrosymmetric zeolite-templated carbon structure
    T. Koretsune, R. Arita and H. Aoki
    Phys. Rev. B 86 (2012) 125207
    A peculiar manifestation of orbital angular momentum is proposed for a zeolite-templated carbon system, C36H9. The structure, being a network of nanoflakes in the shape of a "pinwheel", lacks inversion symmetry. While the unit cell is large, the electronic structure obtained with a first-principles density functional theory and captured as an effective tight-binding model in terms of maximally-localized Wannier functions, exhibits an unusual feature that the valence band top comes from two chiral states having orbital magnetic momenta of 1. The noncentrosymmetric lattice structure then makes the band dispersion asymmetric, as reminiscent of, but totally different from, spin-orbit systems. The unusual feature is predicted to imply a current-induced orbital magnetism when holes are doped.
  • Energetics and electronic properties of twisted single-walled carbon nanotubes
    K. Kato, T. Koretsune and S. Saito
    Phys. Rev. B 85 (2012) 115448
    We perform a systematic first-principles study of energetics and electronic properties of chiral carbon nanotubes (CNTs) in the density-functional theory. It is found that chiral CNTs possess slightly twisted ground-state geometries. Moderate-diameter CNTs show twisting-dependent electronic properties well classified by their chiral indices, while the electronic structures of small-diameter CNTs possess sizable but individually different twisting dependences, leading to metal-semiconductor transitions in some CNTs. The CNT having the widest fundamental gap is predicted to be the twisted (4,3) CNT.
  • One-dimensional alkali-doped C60 chains encapsulated in BN nanotubes
    T. Koretsune, S. Saito and M. L. Cohen
    Phys. Rev. B 83 (2011) 193406
    We study the energetics, electronic structures, and electron-phonon couplings of a one-dimensional potassium-doped C60 chain encapsulated in a boron nitride nanotube using the framework of the density-functional theory. We demonstrate that the reaction of potassium doping is exothermic and the resulting material is one-dimensional metal where conducting electrons are only in the C60 chain. Interestingly, the Fermi-level density of states has a peculiar pressure dependence and can be larger than those in the three-dimensional alkali-doped fullerene compounds, indicating the possibility of various phase transitions. We also discuss the electron-phonon couplings and the possibility of superconductivity.
  • Electronic structure and stability of layered superlattice composed of graphene and boron nitride monolayer
    Y. Sakai, T. Koretsune and S. Saito
    Phys. Rev. B 83 (2011) 205434
    We study superlattices with alternate stacking of graphene and boron nitride monolayers. We propose several candidate stacking sequences of the superlattices, and optimize their geometries based on the energetics in the framework of the density functional theory. From the total energies of the superlattices with the candidate stacking sequences, we identify the most stable stacking sequence. The atomic configuration of the superlattice with the most stable stacking sequence is found to have the shortest B-C distance among all the optimized superlattice geometries, indicating a strong interaction between the carbon and boron atoms. We also study the electronic structure of the superlattices in detail. It is revealed that the most stable structure exhibits metallic electronic properties.
  • "Ab initio derivation of the low-energy model for alkali-cluster-loaded sodalites"
    K. Nakamura, T. Koretsune and R. Arita
    Phys. Rev. B 80 (2009) 174420 (cond-mat/0907.4593v1 )
    An effective low-energy model describing magnetic properties of alkali-cluster-loaded sodalites is derived by ab initio downfolding. We start with constructing an extended Hubbard model for maximally localized Wannier functions. Ab initio screened Coulomb and exchange interactions are calculated by constrained random-phase approximation. We find that the system resides in the strong-coupling regime and thus the Heisenberg model is derived as a low-energy model of the extended Hubbard model. We obtain antiferromagnetic couplings ~O(10 K), being consistent with the experimental temperature dependence of the spin susceptibility. Importance of considering the screening effect in the derivation of the extended Hubbard model is discussed.
  • "Thermodynamic properties of Heisenberg model on a triangular lattice with two exchange couplings: Application to two-dimensional solid 3He adsorbed on graphite"
    T. Koretsune, M. Udagawa and M. Ogata
    Phys. Rev. B 80 (2009) 075408
    To discuss the gapless spin-liquid-like behavior of the second-layer solid-phase 3He adsorbed on graphite, we study a spin-1/2 Heisenberg model on a triangular lattice with two kinds of superexchange couplings due to the corrugation effects from the first-layer by using finite temperature Lanczos method and high-temperature expansions. In some parameter region, it is found that this model can be expressed by an effective Hamiltonian with two different energy scales consisting of kagome Heisenberg model and triangular Heisenberg model. We find that this effective Hamiltonian well reproduces the experimental behaviors such as the double-peak structure and the low-temperature linear-T behavior of the specific heat as well as the excess enhancement of the spin susceptibility at low temperatures.
  • "A new crystalline phase of four-fold coordinated silicon and germanium"
    Y. Fujimoto, T. Koretsune, S. Saito, T. Miyake and A. Oshiyama
    New Journal of Physics 10 (2008) 083001
    We have performed first-principles calculations for body-centered tetragonal (bct) Si and Ge consisting solely of four-fold coordinated elements. The structural optimization has been carried out based on the local density approximation (LDA) in the density functional theory (DFT). For total-energy minimized structures, quasi-particle spectra have been calculated using GW approximation. We find that the bct Si and Ge are new stable crystalline phases reachable under tensile stress with moderate magnitude. We also find that the bct Ge is a semimetal with the carrier density of 2×1019 cm−3, whereas the bct Si is a semiconductor with the indirect band gap of 0.5 eV. The calculated density of states of the bct Si and Ge show characteristic features which are discriminated from those of the diamond structures. Effective masses of conduction-band electrons and valence-band holes are found to be relatively light compared with those of the diamond Si and Ge. The origins of reduction or closure of band gaps are discussed.
  • "Superconductivity in Thin Films of Boron-Doped Carbon Nanotubes"
    N. Murata, J. Haruyama, J. Reppert, A.M. Rao, T. Koretsune, S. Saito, M. Matsudaira and Y. Yagi
    Phys. Rev. Lett. 101 027002 (2008).
  • "Electronic structure of boron-doped carbon nanotube"
    T. Koretsune and S. Saito
    Physical Review B 77 165417 (2008).
    We study boron-doped single-walled carbon nanotubes by using first-principles methods based on the density functional theory. The total energy, band structure, and density of states are calculated. From the formation energy of boron-doped nanotubes with different diameters, it is found that a narrower tube needs a smaller energy cost to substitute a carbon atom with a boron atom. By using the result of different doping rates in the (10,0) tube, we extrapolate the result to low boron density limit and find that the ionization energy of the acceptor impurity level should be approximately 0.2 eV. Furthermore, we discuss the doping rate dependence of the density of states at the Fermi level, which is important to realize superconductivity.
  • "Exact Diagonalization Study of Mott Transition in the Hubbard Model on an Anisotropic Triangular Lattice"
    T. Koretsune, Y. Motome and A. Furusaki
    J. Phys. Soc. Jpn. 76 074719-1-10 (2007).
    We study Mott transition in the two-dimensional Hubbard model on an anisotropic triangular lattice. We use the Lanczos exact diagonalization of finite-size clusters up to eighteen sites, and calculate Drude weight, charge gap, double occupancy and spin structure factor. We average these physical quantities over twisted boundary conditions in order to reduce finite-size effects. We find a signature of the Mott transition in the dependence of the Drude weight and/or charge gap on the system size. We also examine the possibility of antiferromagnetic order from the spin structure factor. Combining these information, we propose a ground-state phase diagram which has a nonmagnetic insulating phase between a metallic phase and an insulating phase with antiferromagnetic order. Finally, we compare our results with those reported in the previous theoretical studies, and discuss the possibility of an unconventional insulating state.
  • "Pairing correlation functions in the triangular t-J model: d-wave and f-wave superconductivity"
    T. Koretsune and M. Ogata
    Phys. Rev. B 72 134513-1-6 (2005).
    Equal-time pairing correlation functions of the two-dimensional t-J model on the triangular lattice are studied using high-temperature expansions method. We calculate the pairing correlation lengths and the effective pairing interactions down to T ∼ 0.2t, and find the growth of pairing correlations. When t > 0 with hole doping, a rapid growth of effective d-wave pairing interaction is found which indicates the resonating-valence-bond superconductivity. In contrast, when t < 0 where the ferromagnetic correlation and antiferromagnetic correlation compete, correlation lengths of triplet pairings as well as d-wave pairing grow at low temperatures, although they do not diverge for T => 0 in the competing region, i.e. near half-filling. On the other hand, around n=0.4, f-wave pairing correlation tends to diverge, although its effective interaction is small. Relation of the present study to the recently discovered superconductor, NaxCoO2 yH2O, is discussed.
  • "Development of superconducting correlation at low temperatures in the two-dimensional t-J model"
    T. Koretsune and M. Ogata
    J. Phys. Soc. Jpn. 74, 1390-1393 (2005).
    The equal-time pairing correlation function of the two-dimensional t-J model on a square lattice is studied using a high-temperature expansion method. The sum of the pairing correlation, its spatial dependence, and the correlation length are obtained as functions of temperature down to T∼0.2t. By comparison of single-particle contributions in the correlation functions, we find an effective attractive interaction between quasi-particles in dx2-y2-wave pairings. It is shown that d-wave correlation grows rapidly at low temperatures for 0.5 < n < 0.9, with n being the electron density. The temperature for this growth is roughly scaled by J/2. This is in sharp contrast to the Hubbard model in a weak or intermediate coupling region, where there is no numerical evidence of superconductivity.
  • "Feromagnetism on the Frustrated Lattices"
    T. Koretsune and M. Ogata
    J. Phys. Soc. Jpn. 72, 2437-2440 (2003).
    The two-dimensional t-J model of the triangular and kagome lattice is studied by high temperature expansions. The analyses of uniform susceptibility as well as the ground-state energy show strong evidence that ferromagnetic ground state exists in a wide region in the phase diagram with resprect to electron density, n, and superexchange coupling, J, which is a different feature from the case of the square lattice. This result means that the low-density region, where the ferromagnetism is understood by Kanamori's mechanism, continues to Nagaoka's ferromagnetism in frustrated lattices. We also find the possibility of partial ferromagnetism in the low-density region of the triangular lattice.
  • "Resonating-Valence-Bond States and Ferromagnetic Correlations in the Doped Triangular Mott Insulator"
    T. Koretsune and M. Ogata
    Phys. Rev. Lett. 89, 116401-1-4 (2002).
    The two-dimensional t-J model on a triangular lattice is studied using high-temperature expansions. By studying the entropy and spin susceptibility, we find that the sign of the hopping integral t is very crucial. In the case of t>0, the peak of the spin susceptibility moves to the high-temperature region with hole doping, which indicates the appearance of the resonating-valence-bond state. In contrast, for t<0, the peak of the spin susceptibility disappears with hole doping and the entropy at low temperatures behaves as S=γT with large coefficient γ, representing a large effective mass. This behavior is understood from the competition between Nagaoka's ferromagnetism and singlet formation.

Proceedings
  • "Electronic structures of hexagonal boron-nitride monolayer: strain-induced effects"
    Y. Fujimoto, T. Koretsune and S. Saito
    J. Ceramic Soc. Jpn. 122 (2014) 346
  • "Electronic structures of carbon-doped hexagonal boron nitride sheet: A density-functional study"
    Y. Fujimoto, T. Koretsune and S. Saito
    JPS Conf. Proc. 1 (2014) 012066
  • "Twisting Effects on Carbon Nanotubes: A First-Principles Study with Helical Symmetry Operations"
    K. Kato, T. Koretsune and S. Saito
    J. Phys: Conf. Ser. 302 (2011) 012007
  • "Electronic structures and three-dimensional effects of the boron-doped carbon nanotubes"
    T. Koretsune and S. Saito
    Sci. Technol. Adv. Mater. 9 (2008) 044203
    We study boron-doped carbon nanotubes by first-principles methods based on the density functional theory. To discuss the possibility of superconductivity, we calculate the electronic band structure and the density of states (DOS) of boron-doped (10,0) nanotubes by changing the boron density. It is found that the Fermi level density of states D(F) increases upon lowering the boron density. This can be understood in terms of the rigid band picture where the one-dimensional van Hove singularity lies at the edge of the valence band in the DOS of the pristine nanotube. The effect of three-dimensionality is also considered by performing the calculations for bundled (10,0) nanotubes and boron-doped double-walled carbon nanotubes (10,0)@(19,0). From the calculation of the bundled nanotubes, it is found that interwall dispersion is sufficiently large to broaden the peaks of the van Hove singularity in the DOS. Thus, to achieve the high D(F) using the bundle of nanotubes with single chirality, we should take into account the distance from each nanotube. In the case of double-walled carbon nanotubes, we find that the holes introduced to the inner tube by boron doping spread also on the outer tube, while the band structure of each tube remains almost unchanged.
  • "Effective mass divergence in the infinite-U Hubbard model"
    T. Koretsune and M. Ogata
    Physica B. 378-380 323-324 (2006).
    To clarify the property of Mott transition in the strong correlation limit, we investigate the infinite-U Hubbard model using high-temperature expansion method. The free energies in various lattices are obtained as a function of inverse temperature and electron density. If we assume the low temperature behavior as ST, we can extrapolate the series down to T=0 with remarkable accuracy and find that the specific heat coefficient γ diverges with n = 1. Furthermore, it is revealed that the divergence is scaled as γ ∝ (1-n)^-x with x ∼ 1.7-1.8, which is almost irrespective of lattice structure.
  • "Possible pairing symmetry in the two-dimensional t-J model on square and triangular lattices"
    T. Koretsune and M. Ogata
    Physica B. 359-361 545-547 (2005).
  • "Effect of a geometrical frustration in the doped Mott insulator"
    T. Koretsune and M. Ogata
    Physica C. 388-389, 88-89 (2003).
  • "The ground state energy and entropy of the two-dimensional t-J model"
    T. Koretsune and M. Ogata
    J. Phys. Chem. Solids 63, 1419-1422 (2002).
    We have studied the entropy of two-dimensional t-J model by high temperature expansions through 14th order in inverse temperature. We extrapolated the series of entropy as a function of internal energy down to T=0 and found that the entropy has wavy form in low doped case. We conclude that this indicate the spin-charge separation.

Books etc.