
Topological Nernst effect emerging from realspace 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)

sparseir: Optimal compression and sparse sampling of manybody 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 roomtemperature superconductivity in LaH10
Tianchun Wang, José A. FloresLivas, Takuya Nomoto, Yanming Ma, Takashi Koretsune, and Ryotaro Arita
Phys. Rev. B 105 174516 (2022)

Wannierbased implementation of the coherent potential approximation with applications to Febased 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 ironbased 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)

Magnetooptical 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)

Xray 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, Takahisa Arima, and Tetsuya Nakamura
Nature Communications 12 5582 (2021)

Absence of conventional roomtemperature superconductivity at high pressure in carbondoped H3S
Tianchun Wang, Motoaki Hirayama, Takuya Nomoto, Takashi Koretsune, Ryotaro Arita, and José A. FloresLivas
Phys. Rev. B 104 064510 (2021)

Effect of symmetry breaking on shortwavelength 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 threedimensional topologicalinsulator–thinfilmferromagneticmetal 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 NishioHamane, Rieko Ishii, Fumiyuki Ishii, Ryotaro Arita and Satoru Nakatsuji
Nature Comm. 12 572 (2021)

Geometrical Hall effect and momentumspace Berry curvature from spinreversed 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 MigdalEliashberg calculation considering the retardation effect in phononmediated superconductors
Tianchun Wang, Takuya Nomoto, Yusuke Nomura, Hiroshi Shinaoka, Junya Otsuki, T. Koretsune, and Ryotaro Arita
Phys. Rev. B 102 134503 (2020)

Giant magnetooptical 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 Gdbased skyrmion materials
Takuya Nomoto, Takashi Koretsune, and Ryotaro Arita
Phys. Rev. Lett. 125 117204 (2020)

Local force method for the ab initio tightbinding model: Effect of spindependent hopping on exchange interactions
Takuya Nomoto, Takashi Koretsune, and Ryotaro Arita
Phys. Rev. B 102 014444 (2020)

Systematic firstprinciples study of the onsite spinorbit coupling in crystals
Kensuke Kurita, Takashi Koretsune
Phys. Rev. B 102 045109 (2020)

Ironbased 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 NishioHamane, Fumiyuki Ishii, Ryotaro Arita and Satoru Nakatsuji
Nature 581 5357 (2020)
Press release

Quantum crystal structure in the 250kelvin 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. FloresLivas
Nature 578 6669 (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, JaeMo 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 Sn1xInxTe
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 hedgehoglattice 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

Negativepressureinduced helimagnetism in ferromagnetic cubic perovskites Sr1xBaxCoO3
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 betaMntype hightemperature 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 AntiThCr2Si2type 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 quantumcritical scaling in a ferromagnetic semimetal
Akito Sakai, Yo Pierre Mizuta, Agustinus Agung Nugroho, Rombang Sihombing, Takashi Koretsune, MichiTo Suzuki, Nayuta Takemori, Rieko Ishii, Daisuke NishioHamane, 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)

Chargetransfer complexes based on C2vsymmetric benzo[ghi]perylene: comparison of their dynamic and electronic properties with those of D6hsymmetric 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 magnetothermopower 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 magnetooptical 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, MichiTo Suzuki, Shreyas Patankar, Muhammad Ikhlas, C. L. Chien, Ryotaro Arita, Robert D. Shull, Joseph Orenstein, and Satoru Nakatsuji
Nature Photonics 12 7378 (2018)
Press release

FirstPrinciples Evaluation of the DzyaloshinskiiMoriya 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 10901095 (2017)
Press release

Efficient method to calculate the electronphonon 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, MichiTo Suzuki, Daisuke NishioHamane, Ryotaro Arita, Yoshichika Otani and Satoru Nakatsuji
Nature Physics 13 10851090 (2017)
Press release

PentagonEmbedded Cycloarylenes with Cylindrical Shapes
Shunpei Hitosugi, Sota Sato, Taisuke Matsuno, Takashi Koretsune, Ryotaro Arita, Hiroyuki Isobe
Angewandte Chemie 56 91069110 (2017)

Weak phononmediated 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)

πelectron S=1/2 quantum spinliquid 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 635643 (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 singlelayer 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 730733 (2017)

Structural Modulation of Macrocyclic Materials for Charge Carrier Transport Layers in Organic LightEmitting 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 LightElement Superconductors
R. Arita, T. Koretsune, S. Sakai, R. Akashi, Y. Nomura, W. Sano
Advanced Materials (2017)

Cationic piStacking Columns of Coronene Molecules with Fully Charged and ChargeDisproportionated States
Y. Yoshida, K. Isomura, M. Maesato, T. Koretsune, Y. Nakano, H. Yamochi, M. Kishida, and G. Saito
Cryst. Growth Des. 16 5994 (2016)

GateTuned Thermoelectric Power in Black Phosphorus
Y. Saito, T. Iizuka, T. Koretsune, R. Arita, S. Shimizu, and Y. Iwasa
Nano Letter 16 4819 (2016)

DzyaloshinskiiMoriya Interaction as a Consequence of a Doppler Shift due to SpinOrbitInduced Intrinsic Spin Current
T. Kikuchi, T. Koretsune, R. Arita, and G. Tatara
Phys. Rev. Lett 116 247201 (2016)
Press release

Twodimensional 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 highTc 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 lightemitting devices with singlelayer 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 896904 (2016)

Inplane 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 DzyaloshinskiiMoriya interaction in Mn_{1x}Fe_{x}Ge: a firstprinciples study
T. Koretsune, N. Nagaosa, and R. Arita
Scientific Reports 5 13302 (2015)

Fielddirection control of the type of charge carriers in nonsymmorphic IrO_{2}
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)

Spindisordered quantum phases in a quasionedimensional 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)
Abstract
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 firstprinciples 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 ondimer 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 κET2Cu2(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
Abstract
We present experimental results on the bandgap energies of homoepitaxial diamond films with isotopic compositions ranging from nearly pure carbon12 (12C) to nearly pure carbon13 (13C). Diamond crystals were grown by microwave plasmaassisted 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 bandgap 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 bandgap renormalization due to electronphonon interaction and is found to be even larger than that at low temperatures. These results unambiguously demonstrate the possibility of bandgap engineering of diamond via control of the isotopic composition.

Magnetoorbital effect without spinorbit interactions in a noncentrosymmetric zeolitetemplated carbon structure
T. Koretsune, R. Arita and H. Aoki
Phys. Rev. B 86 (2012) 125207
Abstract
A peculiar manifestation of orbital angular momentum is proposed for a zeolitetemplated 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 firstprinciples density functional theory and captured as an effective tightbinding model in terms of maximallylocalized 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, spinorbit systems. The unusual feature is predicted to imply a currentinduced orbital magnetism when holes are doped.

Energetics and electronic properties of twisted singlewalled carbon nanotubes
K. Kato, T. Koretsune and S. Saito
Phys. Rev. B 85 (2012) 115448
Abstract
We perform a systematic firstprinciples study of energetics and electronic properties of chiral carbon nanotubes (CNTs) in the densityfunctional theory. It is found that chiral CNTs possess slightly twisted groundstate geometries. Moderatediameter CNTs show twistingdependent electronic properties well classified by their chiral indices, while the electronic structures of smalldiameter CNTs possess sizable but individually different twisting dependences, leading to metalsemiconductor transitions in some CNTs. The CNT having the widest fundamental gap is predicted to be the twisted (4,3) CNT.

Onedimensional alkalidoped C60 chains encapsulated in BN nanotubes
T. Koretsune, S. Saito and M. L. Cohen
Phys. Rev. B 83 (2011) 193406
Abstract
We study the energetics, electronic structures, and electronphonon couplings of a onedimensional potassiumdoped C60 chain encapsulated in a boron nitride nanotube using the framework of the densityfunctional theory. We demonstrate that the reaction of potassium doping is exothermic and the resulting material is onedimensional metal where conducting electrons are only in the C60 chain. Interestingly, the Fermilevel density of states has a peculiar pressure dependence and can be larger than those in the threedimensional alkalidoped fullerene compounds, indicating the possibility of various phase transitions. We also discuss the electronphonon 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
Abstract
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 BC 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 lowenergy model for alkaliclusterloaded sodalites"
K. Nakamura, T. Koretsune and R. Arita
Phys. Rev. B 80 (2009) 174420 (condmat/0907.4593v1 )
Abstract
An effective lowenergy model describing magnetic properties of alkaliclusterloaded 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 randomphase approximation. We find that the system resides in the strongcoupling regime and thus the Heisenberg model is derived as a lowenergy 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 twodimensional solid 3He adsorbed on graphite"
T. Koretsune, M. Udagawa and M. Ogata
Phys. Rev. B 80 (2009) 075408
Abstract
To discuss the gapless spinliquidlike behavior of the secondlayer solidphase 3He adsorbed on graphite, we study a spin1/2 Heisenberg model on a triangular lattice with two kinds of superexchange couplings due to the corrugation effects from the firstlayer by using finite temperature Lanczos method and hightemperature 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 doublepeak structure and the lowtemperature linearT behavior of the specific heat as well as the excess enhancement of the spin susceptibility at low temperatures.

"A new crystalline phase of fourfold coordinated silicon and germanium"
Y. Fujimoto, T. Koretsune, S. Saito, T. Miyake and A. Oshiyama
New Journal of Physics 10 (2008) 083001
Abstract
We have performed firstprinciples calculations for bodycentered tetragonal (bct) Si and Ge consisting solely of fourfold coordinated elements. The structural optimization has been carried out based on the local density approximation (LDA) in the density functional theory (DFT). For totalenergy minimized structures, quasiparticle 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 conductionband electrons and valenceband 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 BoronDoped 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 borondoped carbon nanotube"
T. Koretsune and S. Saito
Physical Review B 77 165417 (2008).
Abstract
We study borondoped singlewalled carbon nanotubes by using firstprinciples methods based on the density functional theory. The total energy, band structure, and density of states are calculated. From the formation energy of borondoped 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 074719110 (2007).
Abstract
We study Mott transition in the twodimensional Hubbard model on an anisotropic triangular lattice. We use the Lanczos exact diagonalization of finitesize 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 finitesize 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 groundstate 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 tJ model: dwave and fwave superconductivity"
T. Koretsune and M. Ogata
Phys. Rev. B 72 13451316 (2005).
Abstract
Equaltime pairing correlation functions of the twodimensional tJ model on the triangular lattice are studied using hightemperature 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 dwave pairing interaction is found which indicates the resonatingvalencebond superconductivity. In contrast, when t < 0 where the ferromagnetic correlation and antiferromagnetic correlation compete, correlation lengths of triplet pairings as well as dwave pairing grow at low temperatures, although they do not diverge for T => 0 in the competing region, i.e. near halffilling. On the other hand, around n=0.4, fwave 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 twodimensional tJ model"
T. Koretsune and M. Ogata
J. Phys. Soc. Jpn. 74, 13901393 (2005).
Abstract
The equaltime pairing correlation function of the twodimensional tJ model on a square lattice is studied using a hightemperature 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 singleparticle contributions in the correlation functions, we find an effective attractive interaction between quasiparticles in dx2y2wave pairings. It is shown that dwave 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, 24372440 (2003).
Abstract
The twodimensional tJ model of the triangular and kagome lattice is studied by high temperature expansions. The analyses of uniform susceptibility as well as the groundstate 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 lowdensity 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 lowdensity region of the triangular lattice.

"ResonatingValenceBond States and Ferromagnetic Correlations in the Doped Triangular Mott Insulator"
T. Koretsune and M. Ogata
Phys. Rev. Lett. 89, 11640114 (2002).
Abstract
The twodimensional tJ model on a triangular lattice is studied using hightemperature 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 hightemperature region with hole doping, which indicates the appearance of the resonatingvalencebond 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.