2024/05/14 更新

ナカムラ カズマ
中村 和磨
NAKAMURA Kazuma
Scopus 論文情報  
総論文数: 0  総Citation: 0  h-index: 10

Citation Countは当該年に発表した論文の被引用数

所属
大学院工学研究院 基礎科学研究系
職名
教授
メールアドレス
メールアドレス
研究室電話
093-884-3419
外部リンク

研究キーワード

  • 第一原理計算

  • 物性理論

取得学位

  • 京都大学  -  博士(理学)   2003年09月

学内職務経歴

  • 2022年03月 - 現在   九州工業大学   大学院工学研究院   基礎科学研究系     教授

  • 2012年10月 - 2022年02月   九州工業大学   大学院工学研究院   基礎科学研究系     准教授

論文

  • Ab initio calculation for electronic structure and optical property of tungsten carbide in a TiCN-based cermet for solar thermal applications 査読有り 国際誌

    Hayakawa S., Chono T., Watanabe K., Kawano S., Nakamura K., Miyazaki K.

    Scientific Reports   13 ( 1 )   2023年06月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present an ab initio calculation to understand electronic structures and optical properties of a tungsten carbide WC being a major component of a TiCN-based cermet. The TiCN-based cermet is widely used as a cutting tool, and is discarded as usual after use. On the other hand, cermet itself is also a famous ingredient of a solar absorption film. We found that the WC has a fairly low-energy plasma excitation ∼ 0.6 eV (2 μ m) and therefore can be a good constituent of a solar selective absorber. The evaluated figure of merit for photothermal conversion is prominently high compared to those of the other materials included in the TiCN-based cermet. The imaginary part of the dielectric function is considerably small around the zero point of the real part of the dielectric function, corresponding to the plasma excitation energy. Therefore, a clear plasma edge appeared, ensuring the high performance of the WC as the solar absorber. This is a fascinating aspect, because the wasted TiCN-based cermet cutting tool can be recycled as the solar absorption film after proper treatments and modifications.

    DOI: 10.1038/s41598-023-36337-4

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  • Insulating Nature of Iridium Oxide Ca<inf>5</inf>Ir<inf>3</inf>O<inf>12</inf> Probed by Synchrotron-Radiation-Based Infrared Spectroscopy 査読有り

    Hanate H., Kawano S., Hayashida M., Nakamura K., Ikemoto Y., Moriwaki T., Hasegawa T., Tsutsui S., Matsuhira K.

    Journal of the Physical Society of Japan   92 ( 6 )   2023年05月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    Ca5Ir3O12 shows semiconducting behavior, although it is expected to have metallic conduction because of its 1/6-filled band. To investigate the insulating nature of Ca5Ir3O12, synchrotron-radiation-based infrared spectroscopy and electrical resistivity measurements were performed. Optical conductivity obtained using Kramers–Krönig transformation is compared with ab initio calculations based on density-functional and random-phase-approximation calculations, and their differences are carefully discussed. A detailed analysis of the temperature dependence of electrical resistivity along the c-axis reveals that ln ρ ∝ T −2/3. This temperature dependence indicates that the electrical conduction of Ca5Ir3O12 along the c-axis follows Efros–Shklovskii variable-range hopping. The optical conductivity with polarization parallel to the c-axis shows no clear onset at 1,300 cm−1 (0.16 eV) of the energy gap obtained by assuming the Arrhenius law. This feature of the optical conductivity is consistent with the fact that Ca5Ir3O12 follows Efros–Shklovskii variable-range hopping.

    DOI: 10.7566/JPSJ.92.064705

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  • Hidden Markov model analysis for fluorescent time series of quantum dots 査読有り

    Tatsuhiro Furuta, Keisuke Hamada, Masaru Oda, and Kazuma Nakamura

    Physical Review B ( American Physical Society )   106 ( 104305 )   1 - 15   2022年09月

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    担当区分:最終著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present a hidden Markov model analysis for fluorescent time series of colloidal quantum dots. A fundamental quantity to measure optical performance of the quantum dots is a distribution function for the light-emission duration. So far, to estimate it, a threshold value for the fluorescent intensity was introduced, and the light-emission state was evaluated as a state above the threshold. With this definition, the light-emission duration was estimated, and its distribution function was derived as a blinking plot. Due to the noise in the fluorescent data, however, this treatment generates a large number of artificially short-lived emission states, thus leading to an erroneous blinking plot. In the present paper, we propose a hidden Markov model to eliminate these artifacts. The hidden Markov model introduces a hidden variable specifying the light-emission and quenching states behind the observed fluorescence. We found that it is possible to avoid the above artifacts by identifying the state from the hidden-variable time series. We found that, from the analysis of experimental and theoretical benchmark data, the accuracy of our hidden Markov model is beyond human cognitive ability.

    DOI: 10.1103/PhysRevB.106.104305

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  • Electronic Correlation Strength of Inorganic Electrides from First Principles 査読有り

    Kanno S., Tada T., Utsumi T., Nakamura K., Hosono H.

    Journal of Physical Chemistry Letters   12 ( 50 )   12020 - 12025   2021年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    Strongly correlated electron systems, generally recognized as d- and f-electron systems, have attracted attention as a platform for the emergence of exotic properties such as high-Tc superconductivity. However, correlated electron behaviors have been recently observed in a group of novel materials, electrides, in which s-electrons are confined in subnanometer-sized spaces. Here, we present a trend of electronic correlation of electrides by evaluating the electronic correlation strength obtained from model parameters characterizing effective Hamiltonians of 19 electrides from first principles. The calculated strengths vary in the order 0D ≫ 1D > 2D ∼ 3D electrides, which corresponds to experimental trends, and exceed 10 (a measure for the emergence of exotic properties) in all of the 0D and some of the 1D electrides. We also found the electronic correlation depends on the cation species surrounding the s-electrons. The results indicate that low-dimensional electrides will be new research targets for studies of strongly correlated electron systems.

    DOI: 10.1021/acs.jpclett.1c03637

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  • Ab initio derivation of low-energy Hamiltonians for systems with strong spin-orbit interaction: Application to Ca5 Ir3 O12 査読有り

    Charlebois M., Morée J.B., Nakamura K., Nomura Y., Tadano T., Yoshimoto Y., Yamaji Y., Hasegawa T., Matsuhira K., Imada M.

    Physical Review B   104 ( 7 )   2021年08月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present an ab initio derivation method for effective low-energy Hamiltonians of material with strong spin-orbit interactions. The effective Hamiltonian is described in terms of the Wannier function in the spinor form, and effective interactions are derived with the constrained random phase approximation (cRPA) method. Based on this formalism and the developed code, we derive an effective Hamiltonian of a strong spin-orbit interaction material Ca5Ir3O12. This system consists of three edge-shared IrO6 octahedral chains arranged along the c axis, and the three Ir atoms in the ab plane compose a triangular lattice. For such a complicated structure, we need to set up the Wannier spinor function under the local coordinate system. We found that a density-functional band structure near the Fermi level is formed by local dxy and dyz orbitals. Then, we constructed the ab initio dxy/dyz model. The estimated nearest-neighbor transfer t is close to 0.2 eV, and the cRPA on-site U and neighboring V electronic interactions are found to be 2.4-2.5 eV and 1 eV, respectively. The resulting characteristic correlation strength defined by (U-V)/t is above 7, and thus this material is classified as a strongly correlated electron system. The on-site transfer integral involved in the spin-orbit interaction is 0.2 eV, which is comparable to the on-site exchange integrals ∼0.2 eV, indicating that the spin-orbit-interaction physics would compete with the Hund physics. Based on these calculated results, we discuss possible rich ground-state low-energy electronic structures of spin, charge, and orbitals with competing Hund, spin-orbit, and strong-correlation physics.

    DOI: 10.1103/PhysRevB.104.075153

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  • RESPACK: An ab initio tool for derivation of effective low-energy model of material 査読有り

    Nakamura K., Yoshimoto Y., Nomura Y., Tadano T., Kawamura M., Kosugi T., Yoshimi K., Misawa T., Motoyama Y.

    Computer Physics Communications   261   2021年04月

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    担当区分:筆頭著者   記述言語:英語   掲載種別:研究論文(学術雑誌)

    RESPACK is a first-principles calculation software for evaluating the interaction parameters of materials and is able to calculate maximally localized Wannier functions, response functions based on the random phase approximation and related optical properties, and frequency-dependent electronic interaction parameters. RESPACK receives its input data from a band-calculation code using norm-conserving pseudopotentials with plane-wave basis sets. Automatic generation scripts that convert the band-structure results to the RESPACK inputs are prepared for xTAPP and Quantum ESPRESSO. An input file for specifying the RESPACK calculation conditions is designed pursuing simplicity and is given in the Fortran namelist format. RESPACK supports hybrid parallelization using OpenMP and MPI and can treat large systems including a few hundred atoms in the calculation cell. Program summary: Program Title: RESPACK CPC Library link to program files: https://dx.doi.org/10.17632/3cxb7474nj.1 Developer's repository link: https://sites.google.com/view/kazuma7k6r Licensing provisions: GNU General Public Licence v3.0 Programming language: FORTRAN, PYTHON External routines: LAPACK, BLAS, MPI Nature of problem: Ab initio calculations for maximally localized Wannier function, response function with random-phase approximation, and matrix-element evaluations of frequency-dependent screened direct and exchange interactions. With this code, an effective low-energy model of materials is derived from first principles. Solution method: Our method is based on ab initio many-body perturbation calculation and the maximally localized Wannier function calculation. The program employs the plane-wave basis set, and evaluations of matrix elements are performed with the fast Fourier transformation. The generalized tetrahedron method is used for the Brillouin Zone integral. Additional comments including restrictions and unusual features: RESPACK supports xTAPP and Quantum ESPRESSO packages, and automatic generation scripts for converting the band-calculation results to the RESPACK inputs are prepared for these software. The current RESPACK only supports band-calculation codes using norm-conserving pseudopotentials with plane-wave basis sets. RESPACK supports hybrid parallelization using OpenMP and MPI to treat large systems in which a few hundred atoms are contained in unit cell.

    DOI: 10.1016/j.cpc.2020.107781

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  • Study of phonon dispersion of iridium oxide Ca5ir3O12 with strong spin–orbit interaction 査読有り

    Hanate H., Hasegawa T., Tsutsui S., Nakamura K., Yoshimoto Y., Kishigami N., Haneta S., Matsuhira K.

    Journal of the Physical Society of Japan   89 ( 5 )   2020年05月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    In this study, we report the results of experiments and calculations of phonon dispersion of iridium oxide with a strong spin–orbit interaction (SOI). Using inelastic X-ray scattering (IXS), we measured the IXS spectra of Ca5Ir3O12 along Γ–A, Γ–M, and Γ–K–M directions in the Brillouin zone of a hexagonal lattice at room temperature. We also show ab initio density-functional phonon dispersions based on local density approximation and generalized gradient approximation (GGA) considering SOI. By comparing the experimental and calculated results, we found that the GGA phonon dispersion with SOI is in very good agreement with the experimental results. The phonon calculation was performed for supercells of 1 × 1 × 3 and preliminary 2 × 2 × 1. We found no phonon instability within these supercells. Low-energy phonon properties such as Debye temperature, specific heat, and sound velocity are also discussed.

    DOI: 10.7566/JPSJ.89.053601

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  • Raman scattering investigation of structural transition in Ca 5 ir 3 O 12 査読有り 国際誌

    Hasegawa T., Yoshida W., Nakamura K., Ogita N., Matsuhira K.

    Journal of the Physical Society of Japan   89 ( 5 )   2020年05月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We report a study of the second-order phase transition at 105 K in the geometrically frustrated iridate Ca5Ir3O12 using a Raman scattering method. The Raman scattering spectra of a single crystal were measured from 4 K to room temperature. Ab initio phonon calculations that consider the spin–orbit interaction were also conducted and compared with the experimental spectra. Agreement between the theoretical and experimental results at room temperature is reasonably good. At room temperature, 6A01 þ 9E0 þ 5E00 were assigned among the Raman active modes, 6A01 þ 13E0 þ 6E00, based on the reported P62 m crystal structure. Below Ts, 23 additional peaks were observed, suggesting the appearance of a superlattice structure. The polarization dependence of Raman spectra below Ts indicates the existence of 6 symmetry. We observed at least one additional mode as a broad weak-intensity peak at temperatures higher than Ts. This suggests possible local distortion around the Ir ions, which would be expected for Ir ions with mixed valence states.

    DOI: 10.7566/JPSJ.89.054602

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  • Raman Scattering Investigation of Structural Transition in Ca5Ir3O12 査読有り

    Hasegawa Takumi, Yoshida Wataru, Nakamura Kazuma, Ogita Norio, Matsuhira Kazuyuki

    Journal of the Physical Society of Japan ( Physical Society of Japan )   89 ( 5 )   54602 - 54602   2020年05月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

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    その他リンク: https://ci.nii.ac.jp/naid/210000158158

  • Harmonic voltage response to AC current in the nonlinear conductivity of iridium oxide Ca5Ir3O12 査読有り

    Hanate H., Nakamura K., Matsuhira K.

    Journal of Magnetism and Magnetic Materials   498   2020年03月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    © 2019 Elsevier B.V. We have carried out harmonic voltage response experiments by application of AC current along the c-axis of Ca5Ir3O12, which has a nonlinear electrical conductivity in a non-ordered state. This AC current method can allow us to investigate a detail of the nonlinear conductivity by application of small current. We observed the harmonics up to 7th order below 200 K. The results reveal that the nonlinear conductivity exists even in application of current close to zero. In addition, the temperature dependence of the resistance R0 estimated at the zero current limit is expressed by ln R0∝T-2/3, which is explained by an adaptation of Efros-Shklovskii variable range hopping or Fogler-Teber-Shklovskii variable range hopping. As a field assisted motion of charge career occurs in hopping conduction, from this analysis result, the nonlinear conductivity comes form the field-assisted hopping conduction.

    DOI: 10.1016/j.jmmm.2019.166203

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  • NdNiO2における自己ドープ型2次元単軌道強相関系の形成

    平山 元昭, 野村 悠祐, 只野 央将, 吉本 芳英, 中村 和磨, 有田 亮太郎

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   75.1 ( 0 )   1710 - 1710   2020年01月

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    記述言語:日本語   掲載種別:研究論文(その他学術会議資料等)

    DOI: 10.11316/jpsgaiyo.75.1.0_1710

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  • Formation of a two-dimensional single-component correlated electron system and band engineering in the nickelate superconductor NdNiO2 査読有り

    Yusuke Nomura, Motoaki Hirayama, Terumasa Tadano, Yoshihide Yoshimoto, Kazuma Nakamura, Ryotaro Arita

    Physical Review B ( American Physical Society )   100 ( 20 )   205138   2019年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    Motivated by the recent experimental discovery of superconductivity in the infinite-layer nickelate Nd0.8Sr0.2NiO2 [Li et al., Nature (London) 572, 624 (2019)], we study how the correlated Ni 3dx2-y2 electrons in the NiO2 layer interact with the electrons in the Nd layer. We show that three orbitals are necessary to represent the electronic structure around the Fermi level: Ni 3dx2-y2, Nd 5d3z2-r2, and a bonding orbital made from an interstitial s orbital in the Nd layer and the Nd 5dxy orbital. By constructing a three-orbital model for these states, we find that the hybridization between the Ni 3dx2-y2 state and the states in the Nd layer is tiny. We also find that the metallic screening by the Nd layer is not so effective in that it reduces the Hubbard U between the Ni 3dx2-y2 electrons just by 10%-20%. On the other hand, the electron-phonon coupling is not strong enough to mediate superconductivity of Tc ∼ 10 K. These results indicate that NdNiO2 hosts an almost isolated correlated 3dx2-y2 orbital system. We further study the possibility of realizing a more ideal single-orbital system in the Mott-Hubbard regime. We find that the Fermi pockets formed by the Nd-layer states dramatically shrink when the hybridization between the interstitial s state and Nd 5dxy state becomes small. By an extensive materials search, we find that the Fermi pockets almost disappear in NaNd2NiO4 and NaCa2NiO3

    DOI: 10.1103/PhysRevB.100.205138

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  • Anisotropic compression effects on nanocrystalline crystals of nickel oxide 査読有り

    Mito M., Tajiri T., Saisho S., Deguchi H., Kohno A., Nakamura K.

    Journal of Magnetism and Magnetic Materials   489   2019年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    © 2019 Elsevier B.V. Nickel oxide (NiO) with bulk crystalline size is an antiferromagnetic insulator correlated strongly with crystal structure. A reduction in crystalline size causes a change in the magnetic sublattice, resulting in the appearance of ferromagnetic moments. Furthermore, in the nano crystals fabricated in mesoporous silica, there is a lattice distortion at the unit cell level that brings about the change in the magnetic property, suggesting a prominent magneto-structural correlation. We investigate anisotropic compression effects on nanocrystalline NiO with a crystalline size (D) of 11.4 nm to observe this remarkable magneto-structural correlation. Magneto-crystalline anisotropy is at its maximum when negative contraction occurs. The negative contraction appears even in a bulk crystal under non-ideal hydrostatic compression, and its anomalous structural change is suppressed with decreasing D.

    DOI: 10.1016/j.jmmm.2019.165407

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  • Hydrostatic pressure effects on superconducting transition of nanostructured niobium highly strained by high-pressure torsion 査読有り 国際誌

    Mito M., Kitamura Y., Tajiri T., Nakamura K., Shiraishi R., Ogata K., Deguchi H., Yamaguchi T., Takeshita N., Nishizaki T., Edalati K., Horita Z.

    Journal of Applied Physics   125 ( 12 )   2019年03月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    © 2019 Author(s). We study the effects of hydrostatic pressure (HP) compression on the superconducting transition of severely strained Nb samples, whose grain sizes are reduced to the submicrometer level. Engineered granularity by high-pressure torsion (HPT) treatment changes the strength of coupling between submicrometer-scale grains and introduces lattice strain. We attempt to utilize the initially accumulated shear strain in the starting material for increasing the superconducting transition temperature T c under HP compression. The HP effects on non-strained Nb have already been investigated in the pressure regime over 100 GPa by Struzhkin et al. [Phys. Rev. Lett. 79, 4262 (1997)], and T c reportedly exhibited an increase from 9.2 to 9.9 K at approximately 10 GPa. (1) Slightly strained Nb in the HPT treatment exhibits the increase in T c under HP due to the strengthening of the intergrain coupling, so the pressure scale of the pressure response observed by Struzhkin et al. is reduced to approximately one-seventh at the maximum. (2) Prominently strained Nb in the HPT treatment exhibits the increase in T c under HP due to a reduction in structural symmetry at the unit-cell level: In a Nb sample subjected to HPT (6 GPa, 10 revolutions), T c exceeds 9.9 K at approximately 2 GPa. According to our first-principle calculations, the reduction in the structural symmetry affords an increase in the density of states at the Fermi energy, thereby yielding a prominent increase in T c at low pressures.

    DOI: 10.1063/1.5083094

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  • 銅酸化物超伝導体の一軸圧縮効果 招待有り 査読有り 国際誌

    美藤 正樹, 中村 和磨, 松本 要, 高野 義彦

    高圧力の科学と技術 ( 日本高圧力学会 )   29 ( 4 )   262 - 271   2019年01月

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    記述言語:英語   掲載種別:記事・総説・解説・論説等(学術雑誌)

    <p>In this article, uniaxial compression effects on cuprate superconductors such as YBa<sub>2</sub>Cu<sub>4</sub>O<sub>8</sub> [Y-124], Y<sub>0.98</sub>Ca<sub>0.02</sub>Ba<sub>2</sub>Cu<sub>4</sub>O<sub>8</sub> [Y<sub>0.98</sub>Ca<sub>0.02</sub>-124], and Hg<sub>0.83</sub>Re<sub>0.18</sub>Ba<sub>2</sub>Ca<sub>2.4</sub>Cu<sub>3.6</sub>O<sub>14</sub> [Hg<sub>0.83</sub>(Re<sub>0.18</sub>)-1223] were reviewed. The uniaxial compression effects were compared with the hydrostatic compression effects via measuring the Meissner signal of their single crystals in the setup of using a diamond anvil cell. In Y-124 and Y<sub>0.98</sub>Ca<sub>0.02</sub>-124, the disappearance of the Meissner signal depended on the style of compression, and the difference in the change in the superconducting transition temperature <i>T</i><sub>c</sub> against initial compression are discussed with the structural symmetry of the CuO<sub>5</sub> pyramid. In Hg<sub>0.83</sub>(Re<sub>0.18</sub>)-1223, the mechanism of increasing <i>T</i><sub>c</sub> is discussed on the basis of the first principle calculation.</p>

    DOI: 10.4131/jshpreview.29.262

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  • 第一原理計算に基づく熱力学状態図作成

    中村 和磨, 飯久 保智

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   74.1 ( 0 )   2961 - 2961   2019年01月

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    担当区分:筆頭著者   記述言語:日本語   掲載種別:研究論文(その他学術会議資料等)

    DOI: 10.11316/jpsgaiyo.74.1.0_2961

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  • X線非弾性散乱による幾何学的フラストレート系イリジウム酸化物Ca<sub>5</sub>Ir<sub>3</sub>O<sub>12</sub>のフォノン分散の研究

    花手 洋樹, 中村 和磨, 松平 和之, 岸上 尚弘, 羽根田 翔, 長谷川 巧, 筒井 智嗣

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   74.2 ( 0 )   1876 - 1876   2019年01月

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    記述言語:日本語   掲載種別:研究論文(その他学術会議資料等)

    DOI: 10.11316/jpsgaiyo.74.2.0_1876

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  • 幾何学的フラストレート系イリジウム酸化物Ca<sub>5</sub>Ir<sub>3</sub>O<sub>12</sub>の非線形伝導による高調波応答の研究

    花手 洋樹, 中村 和磨, 松平 和之

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   74.1 ( 0 )   2311 - 2311   2019年01月

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    記述言語:日本語   掲載種別:研究論文(その他学術会議資料等)

    DOI: 10.11316/jpsgaiyo.74.1.0_2311

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  • Hydrostatic compression effects on fifth-group element superconductors V, Nb, and Ta subjected to high-pressure torsion 査読有り 国際誌

    Mito M., Shigeoka S., Kondo H., Noumi N., Kitamura Y., Irie K., Nakamura K., Takagi S., Deguchi H., Tajiri T., Ishizuka M., Nishizaki T., Edalati K., Horita Z.

    Materials Transactions ( 公益社団法人 日本金属学会 )   60 ( 8 )   1472 - 1483   2019年01月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    © 2019 The Japan Institute of Metals and Materials In fifth-group element superconductors V, Nb, and Ta, the increase in superconducting transition temperature (Tc) was attempted by using both high-pressure torsion (HPT) and additional hydrostatic pressure (HP) compression. The former brings about the grain refinement and strain accumulation in the unit-cell level. The additional compression for severely strained superconductors triggers strengthening intergrain-contact and/or structural deformation in the unit-cell level. The manner of the appearance of the above two effects depends on the kind of elements: First, in V, there is no prominent effect of HPT, comparing to the hydrostatic compression effects on its non-strained material. Next, in Ta, the effect of strengthening intergrain-contact appears at small hydrostatic compression, resulting in temporal increase in Tc. Finally, Nb exhibits prominent increase in Tc by both effects and, in particular, the structural deformation in the unit-cell level promotes the increase in Tc. Thus, the accumulation of residual strain in the level of starting material can be a promising work to manipulate Tc under HP compression.

    DOI: 10.2320/matertrans.MF201932

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  • Nonlinear conductivity of geometrically frustrated iridate Ca5Ir3O12 査読有り 国際誌

    Matsuhira K., Nakamura K., Yasukuni Y., Yoshimoto Y., Hirai D., Hiroi Z.

    Journal of the Physical Society of Japan   87 ( 1 )   2018年01月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    © 2018 The Physical Society of Japan. We report the discovery of nonlinear conductivity along the c-axis in a single crystal of Ca5Ir3O12, which indicates a semiconducting behavior with a narrow band gap of ∼0.2 eV. The resistivity decreases with increase in the applied current. This nonlinearity is reversible with the direction of current. We also show the ab initio density functional band structures and the Fermi surface. We found that the spin-orbit interactions result in an appreciable change in the lowenergy electronic structure; the interaction splits the metallic bands and leads to a pocket-like band structure, thus reducing the metallic trend. The size of the spin-orbit interaction is estimated as ∼0.3 eV, which is large enough to be comparable to the valence bandwidth of ∼0.5 eV. The Fermi surface exhibits a sheet structure along the c∗-axis, due to the 1D chain structure of edge-sharing IrO6.

    DOI: 10.7566/JPSJ.87.013703

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  • 幾何学的フラストレート系イリジウム酸化物Ca<sub>5</sub>Ir<sub>3</sub>O<sub>12</sub>の非線形伝導と105K相転移

    松平 和之, 花手 洋樹, 中村 和磨, 矢島 健, 長谷川 巧

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   73 ( 0 )   1440 - 1440   2018年01月

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    記述言語:日本語   掲載種別:研究論文(研究会,シンポジウム資料等)

    DOI: 10.11316/jpsgaiyo.73.2.0_1440

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    その他リンク: https://ci.nii.ac.jp/naid/130007735210

  • USPEXによる非経験的新物質探索:水素化物への応用

    中村 和磨, 飯久保 智

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   73.1 ( 0 )   2678 - 2678   2018年01月

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    担当区分:筆頭著者   記述言語:日本語   掲載種別:研究論文(その他学術会議資料等)

    DOI: 10.11316/jpsgaiyo.73.1.0_2678

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  • 幾何学的フラストレート系イリジウム酸化物Ca<sub>5</sub>Ir<sub>3</sub>O<sub>12</sub>の非線形伝導

    松平 和之, 吉田 航, 安國 友貴, 中村 和磨, 吉本 芳英, 平井 大悟郎, 廣井 善二

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   73 ( 0 )   2044 - 2044   2018年01月

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    記述言語:日本語   掲載種別:研究論文(研究会,シンポジウム資料等)

    DOI: 10.11316/jpsgaiyo.73.1.0_2044

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    その他リンク: https://ci.nii.ac.jp/naid/130007647045

  • Uniaxial strain effects on the superconducting transition in Re-doped Hg-1223 cuprate superconductors 査読有り 国際誌

    Mito M., Ogata K., Goto H., Tsuruta K., Nakamura K., Deguchi H., Horide T., Matsumoto K., Tajiri T., Hara H., Ozaki T., Takeya H., Takano Y.

    Physical Review B   95 ( 6 )   2017年02月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    © 2017 American Physical Society. The effects of uniaxial strain and hydrostatic pressure on Hg0.83Re0.18Ba2Ca2.4Cu3.6O14[Hg0.83(Re0.18)-1223] were investigated by ac magnetic measurements under stress corresponding to a pressure of 20 GPa at maximum. According to a previous thermal study based on the Ehrenfest relation, in-plane contraction should increase the superconducting transition temperature Tc, whereas out-of-plane contraction should decrease Tc. This suggests that the increase in Tc under hydrostatic-pressure contraction must be smaller than that under in-plane contraction. However, the present uniaxial-strain experiments revealed enhancement of Tc under both in-plane and out-of-plane contraction, and the largest enhancement was observed under hydrostatic-pressure contraction. According to a band calculation, all contraction styles induce hole doping from the HgO blocks to the CuO2 blocks, and hydrostatic-pressure contraction yields the largest hole doping among three contractions. This behavior explains well a series of changes in Tc in the stress region of below 8 GPa. More specifically, under hydrostatic-pressure contraction, Tc exhibited an increase, a decrease, and another increase with increasing pressure, and this multistep change is similar to that observed in Bi-2223-type cuprate superconductors, suggesting that it is necessary to distinguish the effect of strain on the middle CuO2 plane in the three-CuO2-plane package from that on the outer planes.

    DOI: 10.1103/PhysRevB.95.064503

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  • 幾何学的フラストレート系イリジウム酸化物Ca5Ir3O12の磁性と電気伝導

    松平 和之, 安國 友貴, 中村 和磨, 吉本 芳英, 平井 大悟郎, 廣井 善二

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   72 ( 0 )   1788 - 1788   2017年01月

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    記述言語:日本語   掲載種別:研究論文(その他学術会議資料等)

    DOI: 10.11316/jpsgaiyo.72.2.0_1788

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    その他リンク: https://ci.nii.ac.jp/naid/130007508009

  • 幾何学的フラストレート系イリジウム酸化物Ca<sub>5</sub>Ir<sub>3</sub>O<sub>12</sub>の輸送特性

    松平 和之, 安國 友貴, 岡 知春, 分島 亮, 日夏 幸雄, 中村 和磨, 吉本 芳英, 長谷川 巧, 廣井 善二

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   72.1 ( 0 )   2327 - 2327   2017年01月

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    記述言語:日本語   掲載種別:研究論文(その他学術会議資料等)

    <p>イリジウム酸化物Ca_5_Ir_3_O_12_はIrが+4.67と中間価数状態にあり,IrO_6_の1次元的な辺共有からなる1次元鎖が三角格子をなした幾何学的にフラストレートした強相関5d電子系物質である。今回,Caサイトの元素置換によるIrサイトへのキャリアドープ(電子ドープおよびホールドープ)した電気抵抗および熱電能におけるキャリアドープ効果について報告する。また,最近得られた単結晶試料の輸送特性などについても報告する。</p>

    DOI: 10.11316/jpsgaiyo.72.1.0_2327

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  • Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain 査読有り 国際誌

    Mito M., Matsui H., Tsuruta K., Yamaguchi T., Nakamura K., Deguchi H., Shirakawa N., Adachi H., Yamasaki T., Iwaoka H., Ikoma Y., Horita Z.

    Scientific Reports   6   2016年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    © 2016 The Author(s). Finding a physical approach for increasing the superconducting transition temperature (T c) is a challenge in the field of material science. Shear strain effects on the superconductivity of rhenium were investigated using magnetic measurements, X-ray diffraction, transmission electron microscopy, and first-principles calculations. A large shear strain reduces the grain size and simultaneously expands the unit cells, resulting in an increase in T c. Here we show that this shear strain approach is a new method for enhancing T c and differs from that using hydrostatic strain. The enhancement of T c is explained by an increase in net electron-electron coupling rather than a change in the density of states near the Fermi level. The shear strain effect in rhenium could be a successful example of manipulating Bardeen-Cooper-Schrieffer-type Cooper pairing, in which the unit cell volumes are indeed a key parameter.

    DOI: 10.1038/srep36337

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  • Ab initio GW plus cumulant calculation for isolated band systems: Application to organic conductor (TMTSF)2PF6 and transition-metal oxide SrVO3 査読有り

    Kazuma Nakamura, Yoshiro Nohara, Yoshihide Yosimoto, Yusuke Nomura

    Phys. Rev. B   93 ( 8 )   085124-1 - 085124-13   2016年02月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present ab initio GW plus cumulant-expansion calculations for an organic compound (TMTSF)2PF6 and a transition-metal oxide SrVO3. These materials exhibit characteristic low-energy band structures around the Fermi level, which bring about interesting low-energy properties; the low-energy bands near the Fermi level are isolated from the other bands, and, in the isolated bands, unusually low-energy plasmon excitations occur. To study the effect of this low-energy-plasmon fluctuation on the electronic structure, we calculate spectral functions and photoemission spectra using the ab initio cumulant expansion of the Green's function based on the GW self-energy. We found that the low-energy plasmon fluctuation leads to an appreciable renormalization of the low-energy bands and a transfer of the spectral weight into the incoherent part, thus resulting in an agreement with experimental photoemission data.

    DOI: 10.1103/PhysRevB.93.085124

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  • (x)TAPPおよびpost-TAPPコードを用いた超伝導パラメータ評価

    中村 和磨, 野原 善郎, 吉本 芳英

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   71.2 ( 0 )   2669 - 2669   2016年01月

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    担当区分:筆頭著者   記述言語:日本語   掲載種別:研究論文(学術雑誌)

    <p>第一原理計算汎用コード「TAPP(東京大学 ab initio program package)」および「ポストTAPP」コードを用いた最近の進捗として, 超伝導転移温度パラメータの評価を実装した。計算アルゴリズムおよびコードの紹介と実証研究に関する結果報告を行う。</p>

    DOI: 10.11316/jpsgaiyo.71.2.0_2669

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  • 幾何学的フラストレート系イリジウム酸化物Ca<sub>5</sub>Ir<sub>3</sub>O<sub>12</sub>のキャリアドープ効果

    安國 友貴, 福岡 亮祐, 前田 賢, 分島 亮, 日夏 幸雄, 中村 和磨, 吉本 芳英, 松平 和之

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   71.2 ( 0 )   1955 - 1955   2016年01月

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    記述言語:日本語   掲載種別:研究論文(その他学術会議資料等)

    <p>イリジウム酸化物$\mathrm{Ca_{5} Ir_{3} O_{12}}$ (六方晶)はIrイオンの価数が+4.67と中間価数状態にあり,$\mathrm{Ir O_{6}}$の辺共有からなる1次元鎖が三角格子をなした幾何学的にフラストレートした強相関5d電子系物質である。今回,CaサイトのBiおよび La 置換によるIrサイトへのキャリアドープ(電子ドープ)を行った。磁化,電気抵抗および熱電能におけるキャリアドープ効果について報告する。</p>

    DOI: 10.11316/jpsgaiyo.71.2.0_1955

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  • Effect of Electron-Phonon Interactions on Orbital Fluctuations in Iron-Based Superconductors 査読有り

    Yusuke Nomura, Kazuma Nakamura, and Ryotaro Arita

    Phys. Rev. Lett.   112 ( 2 )   027002-1 - 027002-5   2014年01月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    To investigate the possibility of whether electron-phonon coupling can enhance orbital fluctuations in iron-based superconductors, we develop an ab initio method to construct the effective low-energy models including the phonon-related terms. With the derived effective electron-phonon interactions and phonon frequencies, we estimate the static part (ω=0) of the phonon-mediated effective on site intra- or interorbital electron-electron attractions as ∼-0.4 eV and exchange or pair-hopping terms as ∼-0.02 eV. We analyze the model with the derived interactions together with the Coulomb repulsions within the random phase approximation. We find that the enhancement of the orbital fluctuations due to the electron-phonon interactions is small, and that the spin fluctuations enhanced by the Coulomb repulsions dominate. It leads to the superconducting state with the sign reversal in the gap functions (s± wave). © 2014 American Physical Society.

    DOI: 10.1103/PhysRevLett.112.027002

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  • 8pBK-4 遷移金属酸化物SrvO3およびSrRuO3の第一原理GWスペクトル関数計算(8pBK バナジウム酸化物,領域8(強相関系))

    中村 和磨, 酒井 志朗, 吉本 芳英

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   69 ( 0 )   2014年01月

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    記述言語:日本語   掲載種別:研究論文(研究会,シンポジウム資料等)

    DOI: 10.11316/jpsgaiyo.69.2.3.0_393_4

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    その他リンク: https://ci.nii.ac.jp/naid/110009887625

  • 27pAD-7 第一原理GW計算による低エネルギープラズマロン状態の解析(27pAD 電子系,領域11(物性基礎論・統計力学・流体物理・応用数学・社会経済物理))

    中村 和磨, 酒井 志朗, 吉本 芳英

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   69 ( 0 )   2014年01月

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    記述言語:日本語   掲載種別:研究論文(研究会,シンポジウム資料等)

    DOI: 10.11316/jpsgaiyo.69.1.2.0_298_1

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    その他リンク: https://ci.nii.ac.jp/naid/110009834621

  • GW calculation of plasmon excitations in the quasi-one-dimensional organic compound (TMTSF)2PF6 査読有り

    Kazuma Nakamura, Shiro Sakai, Ryotaro Arita, and Kazuhiko Kuroki

    Phys. Rev. B   88 ( 12 )   125128-1 - 125128-5   2013年09月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present an ab initio GW calculation to study dynamical effects on an organic compound (TMTSF)2PF6. Calculated polarized reflectivities reproduce experimental plasma edges at around 0.2 eV for Eb ′ and 1.0 eV for Ea. The low-energy plasmons come out from the low-energy narrow bands energetically isolated from other higher-energy bands, and affect the low-energy electronic structure via the GW-type self-energy. Because of the quasi-one-dimensional band structure, a distinct plasmaron state is observed along the Y-Γ line and a large plasmon-induced electron scattering is found in the low-energy occupied states along the X-M line. © 2013 American Physical Society.

    DOI: 10.1103/PhysRevB.88.125128

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  • 26aXM-6 動的遮蔽効果を考慮した超伝導密度汎関数理論(26aXM 電子系1,領域11(統計力学,物性基礎論,応用数学,力学,流体物理))

    明石 遼介, 中村 和磨, 有田 亮太郎

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   68 ( 0 )   2013年01月

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    記述言語:日本語   掲載種別:研究論文(研究会,シンポジウム資料等)

    DOI: 10.11316/jpsgaiyo.68.1.2.0_320_1

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    その他リンク: https://ci.nii.ac.jp/naid/110009643566

  • 27pDJ-8 有機導体(TMTSF)_2PF_6に対する第一原理GW計算(擬一次元系,密度波,領域7(分子性個体・有機導体))

    中村 和磨, 酒井 志朗, 有田 亮太郎, 黒木 和彦

    日本物理学会講演概要集 ( 一般社団法人 日本物理学会 )   68 ( 0 )   2013年01月

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    記述言語:日本語   掲載種別:研究論文(研究会,シンポジウム資料等)

    DOI: 10.11316/jpsgaiyo.68.2.4.0_774_3

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    その他リンク: https://ci.nii.ac.jp/naid/110009756148

  • Ab initio two-dimensional multiband low-energy models of EtMe3Sb[Pd(dmit)2]2 and κ-(BEDT-TTF)2Cu(NCS)2 with comparisons to single-band models 査読有り

    Kazuma Nakamura, Yoshihide Yoshimoto, and Masatoshi Imada

    Phys. Rev. B   86 ( 20 )   205117   2012年11月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present ab initio two-dimensional extended Hubbard-type multiband models for EtMe 3Sb[Pd(dmit) 2] 2 (where dmit is 1,3-dithiole-2-thione-4,5-dithiolate) and κ-(BEDT-TTF) 2Cu(NCS) 2 [where BEDT-TTF is bis(ethylenedithio)-tetrathiafulvalene] after a downfolding scheme based on the constrained random-phase approximation (cRPA) and maximally localized Wannier orbitals, together with the dimensional downfolding. In the Pd(dmit) 2 salt, the antibonding state of the highest occupied molecular orbital (HOMO) and the bonding/antibonding states of the lowest unoccupied molecular orbital (LUMO) are considered to be the orbital degrees of freedom, while, in the κ-BEDT-TTF salt, the HOMO-antibonding/bonding states are considered. Accordingly, a three-band model for the Pd(dmit) 2 salt and a two-band model for the κ-(BEDT-TTF) salt are derived. We derive single-band models for the HOMO-antibonding state for both of the compounds as well. The HOMO antibonding band of the Pd(dmit) 2 salt has a triangular structure of the transfers with a one-dimensional anisotropy, in contrast to the nearly equilateral triangular structure predicted in the extended Hückel results. The ratio of the larger interchain transfer t b to the intrachain transfer t a is around t b/t a∼0.82. Our calculated screened onsite interaction U and the largest offsite interaction V are ∼0.7 and ∼0.23 eV, respectively, for EtMe 3Sb[Pd(dmit) 2] 2 and ∼0.8 and ∼0.2 eV for κ-(BEDT-TTF) 2Cu(NCS) 2. These values are large enough compared to transfers t as ∼55 meV for the Pd(dmit) 2 salt and ∼65 meV for the κ-BEDT-TTF one, and the resulting large correlation strength (U-V)/t∼10 indicates that the present compounds are classified as the strongly correlated electron systems. In addition, the validity whether the present multiband model can be reduced to the single-band model for the HOMO-antibonding state, widely accepted in the literature, is discussed. For this purpose, we estimated the order of vertex corrections ignored in the cRPA downfolding to the single-band model, which is given by W′/D, where W′ is a full-screened-interaction matrix element between the HOMO-antibonding and other bands away from the Fermi level (namely, HOMO-bonding or LUMO-bonding/antibonding bands), whereas D is the energy distance between the Fermi level and the bands away from the Fermi level. In the present materials, W′/D estimated as 0.3-0.5 signals a substantial correction and thus the exchange process between the low-energy HOMO-antibonding and other bands away from the Fermi level may play a key role to the low-energy ground state. This supports that the minimal models to describe the low-energy phenomena of the organic compounds are the multiband models and may not be reduced to the single-band model. © 2012 American Physical Society.

    DOI: 10.1103/PhysRevB.86.205117

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  • High-temperature superconductivity in layered nitrides β-LixMNCl (M = Ti, Zr, Hf): Insights from density functional theory for superconductors 査読有り 国際誌

    Ryosuke Akashi, Kazuma Nakamura, Ryotaro Arita, and Masatoshi Imada

    Phys. Rev. B   86 ( 5 )   054513   2012年08月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present an ab initio analysis with density functional theory for superconductors (SCDFT) to understand the superconducting mechanism of doped layered nitrides β-Li xMNCl (M=Ti, Zr, and Hf). The current version of SCDFT is based on the Migdal-Eliashberg theory and has been shown to reproduce accurately experimental superconducting-transition temperatures T c of a wide range of phonon-mediated superconductors. In the present case, however, our calculated T c≤4.3 K (M=Zr) and ≤10.5 K (M=Hf) are found to be less than half of the experimental T c. In addition, T c obtained in the present calculation increases with increasing doping concentration x, opposite to that observed in the experiment. Our results indicate that we need to consider some factors missing in the current SCDFT based on the Migdal-Eliashberg theory. © 2012 American Physical Society.

    DOI: 10.1103/PhysRevB.86.054513

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  • Effective on-site interaction for dynamical mean-field theory 査読有り

    Yusuke Nomura, Merzuk Kaltak, Kazuma Nakamura, Ciro Taranto, Shiro Sakai, Alessandro Toschi, Ryotaro Arita, Karsten Held, Georg Kresse, and Masatoshi Imada

    Phys. Rev. B   86 ( 8 )   085117   2012年08月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    A scheme to incorporate nonlocal polarizations into the dynamical mean-field theory (DMFT) and a tailor-made way to determine the effective interaction for DMFT are systematically investigated. Applying it to the two-dimensional Hubbard model, we find that nonlocal polarizations induce a nontrivial filling-dependent antiscreening effect for the effective interaction. The present scheme combined with density functional theory offers an ab initio way to derive effective on-site interactions for the impurity problem in DMFT. We apply it to SrVO3 and find that the antiscreening competes with the screening caused by the off-site interaction. © 2012 American Physical Society.

    DOI: 10.1103/PhysRevB.86.085117

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  • Ab Initio Evidence for Strong Correlation Associated with Mott Proximity in Iron-Based Superconductors 査読有り

    Takahiro Misawa, Kazuma Nakamura, and Masatoshi Imada

    Phys. Rev. Lett.   108 ( 17 )   177007   2012年04月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We predict that iron-based superconductors discovered near d6 configuration (5 Fe 3d orbitals filled by 6 electrons) is located on the foot of an unexpectedly large dome of correlated electron matter centered at the Mott insulator at d5 (namely, half filling). This is based on the many-variable variational Monte Carlo results for abinitio low-energy models derived by the downfolding. The d5 Mott proximity extends to subsequent emergence of incoherent metals, orbital differentiations due to the Mott physics, and Hund's rule coupling, followed by antiferromagnetic quantum criticality, in quantitative accordance with available experiments. © 2012 American Physical Society.

    DOI: 10.1103/PhysRevLett.108.177007

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  • Ab initio derivation of electronic low-energy models for C60 and aromatic compounds 査読有り

    Yusuke Nomura, Kazuma Nakamura, and Ryotaro Arita

    Phys. Rev. B   85 ( 15 )   155452   2012年04月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present a systematic study for understanding the relation between electronic correlation and superconductivity in C 60 and aromatic compounds. We derived, from first principles, extended Hubbard models for twelve compounds: fcc K 3C 60, Rb 3C 60, Cs 3C 60 (with three different lattice constants), A15 Cs 3C 60 (with four different lattice constants), doped solid picene, coronene, and phenanthrene. We show that these compounds are strongly correlated and have similar energy scales of their bandwidths and interaction parameters. However, they have a different trend in the relation between the strength of the electronic correlation and superconducting- transition temperature. While the C 60 compounds have a positive correlation, the aromatic compounds exhibit a negative correlation. © 2012 American Physical Society.

    DOI: 10.1103/PhysRevB.85.155452

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  • Effects of transition-metal substitution in the iron-based superconductor LaFeAsO: Momentum- and real-space analysis from first principles 査読有り

    Konbu S., Nakamura K., Ikeda H., Arita R.

    Solid State Communications   152 ( 8 )   728 - 734   2012年04月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We study how transition-metal substitution changes the electronic structure of the iron-based superconductor LaFeAsO in real and momentum space. We first perform ab initio density functional calculation for various sizes of supercells with one transition-metal impurity. For various substitutes (Mn, Co, Ni, Zn, and Ru), we derive effective tight-binding models by constructing the maximally localized Wannier functions from the d bands around the Fermi level. The local electronic structure around the impurity site is quantitatively characterized by their onsite potential and transfer hoppings to neighboring sites. We find that the impurities are classified into three groups according to the derived parameters. For Mn, Co, and Ni, their impurity 3d levels measured from the Fe 3d level are ∼0.3, -0.3, and -0.8 eV, respectively, while, for the Zn case, its d level is extremely deep as ∼8 eV. For the Ru case, although the onsite-level difference is much smaller (∼O(0.1) eV), the transfer integrals around the impurity ion are larger than those of the pure system by 20% ∼ 30%, due to the large spatial spread of the Ru 4d orbitals. We also show that the charge distribution of the extra d electrons is confined around the impurity ion. We then unfold the first Brillouin zone (BZ) for the supercell to calculate the spectral function in the BZ for the normal cell for the case of Co and Ni doping. While the charge distribution seems to suggest that Co and Ni impurities do not change the amount of mobile carriers in the system, the momentum-space analysis clearly shows that the Fermi-surface volume indeed expands by Co and Ni substitutions, which can be well described by the rigid-band shift approximation. © 2012 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ssc.2011.12.048

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  • Mott Transition and Phase Diagram of κ-(BEDT-TTF)2Cu(NCS)2 Studied by Two-Dimensional Model Derived from Ab initio Method 査読有り 国際誌

    Hiroshi Shinaoka, Takahiro Misawa, Kazuma Nakamura, and Masatoshi Imada

    J. Phys. Soc. Jpn   81 ( 3 )   034701   2012年02月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present an ab initio analysis for the ground-state properties of a correlated organic compound κ-(BEDT-TTF) 2Cu(NCS) 2. First, we derive an effective two-dimensional low-energy model from first principles, having shortranged transfers and short-ranged Coulomb and exchange interactions. Then, we perform many-variable variational Monte Carlo calculations for this model and draw a ground-state phase diagram as functions of scaling parameters for the onsite and off-site interactions. The phase diagram consists of three phases; a paramagnetic metallic phase, an antiferromagnetic (Mott) insulating phase, and a charge-ordered phase. In the phase diagram, the parameters for the real compound are close to the first-order Mott transition, being consistent with experiments. We show that the off-site Coulomb and exchange interactions affect the phase boundary; (i) they appreciably stabilize the metallic state against the Mott insulating phase and (ii) enhance charge fluctuations in a wide parameter region in the metallic phase. We observe arc-like structure in Fermi surface around the region where the charge fluctuations are enhanced. Possible relevance of the charge fluctuations to the experimentally observed dielectric anomaly in the κ-BEDT-TTF family compounds is also pointed out. © 2012 The Physical Society of Japan.

    DOI: 10.1143/JPSJ.81.034701

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  • Fermi-suface evolution by transition-metal substitution in the iron-based superconductor LaFeAsO 査読有り

    Konbu S., Nakamura K., Ikeda H., Arita R.

    Journal of the Physical Society of Japan   80 ( 12 )   2011年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We study how Co- and Ni-substitution affect the electronic structure of the iron-based superconductor, LaFeAsO. We perform ab initio supercell calculations and unfold the first Brillouin zone (BZ) to calculate the spectral function in the BZ for the normal cell. The charge density distribution in real space shows that doped extra electrons are trapped around Co (Ni) atom. This seems to suggest that carriers are not doped by Co(Ni)-substitution. However, the present momentum-space analysis indicates that the Fermi-surface volume indeed expands by substitutions, which can be well described by the rigid-band shift approximation. By taking into account this effective doping, we discuss whether the sign-reversing s-wave (s±-wave) scenario is compatible with experiments. © 2011 The Physical Society of Japan.

    DOI: 10.1143/JPSJ.80.123701

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  • Ab initio Derivation of Correlated Superatom Model for Potassium Loaded Zeolite A 査読有り 国際誌

    Yoshiro Nohara, Kazuma Nakamura, and Ryotaro Arita

    J. Phys. Soc. Jpn   80 ( 12 )   124705   2011年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We derive an effective low-energy Hamiltonian for potassium loaded zeolite A, a unique ferromagnet from nonmagnetic elements. We perform ab initio density functional calculations and construct maximally localized Wannier functions for low-energy states made from potassium s electrons. The resulting Wannier orbitals, spreading widely in the alminosilicate cage, are found to be the superatomic s and p orbitals in the confining potential formed by the host cage. We then make a tight-binding model for these superatomic orbitals and introduce interaction parameters such as the Hubbard U. After mean-field calculations for the effective model, we find that ab initio spin density functional results are well reproduced by choosing appropriate sets of the interaction parameters. The interaction parameters turn out to be as large as the band width, ~0.5 eV, indicating the importance of electron correlation, and that the present system is an interesting analog of correlated multi-orbital transition metal oxides. © 2011 The Physical Society of Japan.

    DOI: 10.1143/JPSJ.80.124705

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  • Comparative study of hybrid functionals applied to structural and electronic properties of semiconductors and insulators 査読有り

    Yu-ichiro Matsushita, Kazuma Nakamura, and Atsushi Oshiyama

    Phys. Rev. B   84 ( 7 )   075205   2011年08月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present a systematic study that clarifies the validity and limitation of current hybrid functionals in density functional theory for structural and electronic properties of various semiconductors and insulators. The three hybrid functionals, PBE0 by Perdew, Ernzerhof, and Burke, HSE by Heyd, Scuseria, and Ernzerhof, and a long-range corrected (LC) functional, are implemented in a well-established plane-wave-basis-set scheme combined with norm-conserving pseudopotentials, thus enabling us to assess the applicability of each functional on an equal footing to the properties of the materials. The materials we have examined range from covalent to ionic materials as well as a rare-gas solid whose energy gaps determined by experiments are in the range of 0.6-14.2 eV, i.e., Ge, Si, BaTiO3, β-GaN, diamond, MgO, NaCl, LiCl, Kr, and LiF. We find that the calculated bulk moduli by the hybrid functionals show better agreement with the experiments than that provided by the generalized-gradient approximation (GGA), whereas the calculated lattice constants by the hybrid functionals and the GGA show comparable accuracy. The calculated energy band gaps and the valence-band widths for the ten prototype materials show substantial improvement using the hybrid functional compared with the GGA. In particular, it is found that the band gaps of the ionic materials as well as the rare-gas solid are well reproduced by the LC-hybrid functional, whereas those of covalent materials are well described by the HSE functional. We also examine exchange effects due to short-range and long-range components of the Coulomb interaction, and we propose an optimum recipe to the short-range and long-range separation in treating the exchange energy. © 2011 American Physical Society.

    DOI: 10.1103/PhysRevB.84.075205

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  • First-principles calculation of transition-metal impurities in LaFeAsO 査読有り

    Kazuma Nakamura, Ryotaro Arita, and Hiroaki Ikeda

    Phys. Rev. B   83 ( 14 )   144512   2011年04月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present a systematic ab initio study based on density functional calculations to understand impurity effects in iron-based superconductors. Effective tight-binding Hamiltonians for the d bands of LaFeAsO with various transition-metal impurities such as Mn, Co, Ni, Zn, and Ru are constructed using maximally localized Wannier orbitals. Local electronic structures around the impurity are quantitatively characterized by their onsite potential and transfer hoppings to neighboring sites. We found that the impurities are classified into three groups according to the derived parameters: For Mn, Co, and Ni, their impurity 3d levels measured from the Fe 3d level are nearly, 0.3-0.3, and -0.8 eV, respectively, while, for the Zn case, the d level is considerably deep as -8 eV. For the Ru case, although the onsite-level difference is much smaller as O(0.1) eV, the transfer integrals around the impurity site are larger than those of the pure system by 20% ~ 30%, due to the large spatial spread of the Ru 4d orbitals. We also show that, while excess carriers are tightly trapped around the impurity site (due to the Friedel sum rule), there is a rigid shift of band structure near the Fermi level, which has the same effect as carrier doping. © 2011 American Physical Society.

    DOI: 10.1103/PhysRevB.83.144512

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  • Magnetic Properties of Ab initio Model of Iron-Based Superconductors LaFeAsO 査読有り 国際誌

    Takahiro Misawa, Kazuma Nakamura, and Masatoshi Imada

    J. Phys. Soc. Jpn   80 ( 2 )   023704   2011年01月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    By using a variational Monte Carlo method, we examine an effective low-energy model for LaFeAsO derived from an ab initio downfolding scheme. We show that quantum and many-body fluctuations near the antiferromagnetic (AF) quantum critical point largely reduce the antiferromagnetic ordered moment. Our derived model not only quantitatively reproduces the small ordered moment in LaFeAsO, but also accounts for the diversity from LaFePO, BaFe 2As2 to FeTe. Electron correlation is found to determine the observed material dependence. We also find that LaFeAsO is subject to large orbital fluctuations, sandwiched by the AF Mott insulator and weakly correlated metals. The orbital fluctuations and Dirac-cone dispersion hold keys for the diverse magnetic properties. © 2011 The Physical Society of Japan.

    DOI: 10.1143/JPSJ.80.023704

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  • Ab initio Low-Dimensional Physics Opened Up by Dimensional Downfolding: Application to LaFeAsO 査読有り

    Kazuma Nakamura, Yoshihide Yoshimoto, Yoshiro Nohara, and Masatoshi Imada

    J. Phys. Soc. Jpn   79 ( 12 )   123708   2010年12月

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    担当区分:筆頭著者, 責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)

    An ab initio downfolding method is formulated to construct low-dimensional models for correlated electrons. In addition to band downfolding by a constrained random phase approximation formulated for 3D models, screening away from the target layer (chain) is further involved. Eliminating the off-target degrees of freedom, namely, dimensional downfolding, yields ab initio low-dimensional models. The method is applied to derive a 2D model for the layered superconductor LaFeAsO, where interlayer screening crucially makes the effective interaction short-ranged and reduces the onsite Coulomb interactions by 10-20% compared with the 3D model for the five iron-3d orbitals. © 2010 The Physical Society of Japan.

    DOI: 10.1143/JPSJ.79.123708

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  • Magnetic properties of diluted magnetic semiconductors: Quantum Monte Carlo approach 査読有り 国際誌

    Ohe J., Tomoda Y., Bulut N., Arita R., Nakamura K., Maekawa S.

    Journal of Magnetism and Magnetic Materials   322 ( 9-12 )   1192 - 1194   2010年05月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    The magnetic correlation between magnetic impurities in semiconductors is investigated by performing the quantum Monte Carlo (QMC) simulation. The Anderson Hamiltonian with the realistic parameters obtained by the local density approximation (LDA) calculation is employed. The LDA calculation gives a dispersion of the host (GaAs) electron and the mixing energy between host and magnetic impurity (Mn). The mixing between host and impurity electrons generates the impurity bound state in the energy gap of semiconductors. The long range ferromagnetic coupling is observed when the Fermi energy locates between the band edge and the impurity bound state. The ferromagnetic coupling is enhanced by decreasing temperature. © 2009 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jmmm.2009.06.037

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  • Local atomic structure of superconducting FeSe<inf>1-x</inf>Te<inf>x</inf> 査読有り 国際誌

    Louca D., Horigane K., Llobet A., Arita R., Ji S., Katayama N., Konbu S., Nakamura K., Koo T., Tong P., Yamada K.

    Physical Review B - Condensed Matter and Materials Physics   81 ( 13 )   2010年04月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    The isovalent substitution of Te for Se in the superconducting α-FeSe raises TCwhere the average chalcogen-Fe bond angle decreases and the chalcogen-Fe distance increases. Locally, however, the Se and Te ions do not share the same site and have two distinct z coordinates, in contrast to what is presumed in the P4/nmm symmetry. The local bond angle between the chalcogens and Fe increases with the substitution, consistent with the rise in TC, the Fe-Te bonds become shorter than in the binary FeTe, while the Fe-Se bonds stay the same as in the binary. Ab initio calculations based on spin density functional theory yielded an optimized structure with distinct z coordinates for Se and Te, in addition to a stronger hybridization of Te with Fe. © 2010 The American Physical Society.

    DOI: 10.1103/PhysRevB.81.134524

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  • Comparison of Ab initio Low-Energy Models for LaFePO, LaFeAsO, BaFe2As2, LiFeAs, FeSe, and FeTe: Electron Correlation and Covalency 査読有り

    Takashi Miyake, Kazuma Nakamura, Ryotaro Arita, and Masatoshi Imada

    J. Phys. Soc. Jpn   79 ( 4 )   044705   2010年03月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    Effective low-energy Hamiltonians for several different families of iron-based superconductors are compared after deriving them from the downfolding scheme based on first-principles calculations. Systematic dependences of the derived model parameters on the families are elucidated, many of which are understood from the systematic variation of the covalency between Fe-3d and pnictogen-/chalcogenp orbitals. First, LaFePO, LaFeAsO (1111), BaFe 2As2 (122), LiFeAs (111), FeSe, and FeTe (11) have overall similar band structures near the Fermi level, where the total widths of 10-fold Fe-3d bands are mostly around 4.5 eV. However, the derived effective models of the 10-fold Fe-3d bands (d model) for FeSe and FeTe have substantially larger effective onsite Coulomb interactions U ̃ 4:2 and 3.4 eV, respectively, after the screening by electrons on other bands and after averaging over orbitals, as compared to ̃2:5 eV for LaFeAsO. The difference is similar in the effective models containing p orbitals of As, Se or Te (dp or dpp model), where U ranges from ̃4 eV for the 1111 family to ̃7 eV for the 11 family. The exchange interaction J has a similar tendency. The family dependence of models indicates a wide variation ranging from weak correlation regime (LaFePO) to substantially strong correlation regime (FeSe). The origin of the larger effective interaction in the 11 family is ascribed to smaller spread of the Wannier orbitals generating larger bare interaction, and to fewer screening channels by the other bands. This variation is primarily derived from the distance h between the pnictogen/chalcogen position and the Fe layer: The longer h for the 11 family generates more ionic character of the bonding between iron and anion atoms, while the shorter h for the 1111 family leads to more covalent-bonding character, the larger spread of the Wannier orbitals, and more efficient screening by the anion p orbitals. The screened interaction of the d model is strongly orbital dependent, which is also understood from the Wannier spread. The dp and dpp models show much weaker orbital dependence. The larger h also explains why the 10-fold 3d bands for the 11 family are more entangled with the smearing of the "pseudogap" structure above the Fermi level seen in the 1111 family. While the family-dependent semimetallic splitting of the bands primarily consists of dyz/dzx and dx 2-y2 orbitals, the size of the pseudogap structure is controlled by the hybridization between these orbitals and dxy/ d3z2-r2 : A large hybridization in the 1111 family generates a large "band-insulating"-like pseudogap (hybridization gap), whereas a large h in the 11 family weakens them, resulting in a "half-filled" like bands of orbitals. This may enhance strong correlation effects in analogy with Mott physics and causes the orbital selective crossover in the three orbitals. On the other hand, the geometrical frustration t'/t, inferred from the ratio of the next-nearest transfer t0 to the nearest one t of the d model is relatively larger for the 1111 family than the 11 one. The models comprehensively derived here may serve as a firm starting basis of understanding both common and diverse properties of the iron-based superconductors including magnetism and superconductivity. © 2010 The Physical Society of Japan.

    DOI: 10.1143/JPSJ.79.044705

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  • Spin density functional study of magnetism in potassium-loaded zeolite A 査読有り

    Nohara Y., Nakamura K., Arita R.

    Physical Review B - Condensed Matter and Materials Physics   80 ( 22 )   2009年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    In order to clarify the mechanism of spin polarization in potassium-loaded zeolite A, we perform ab initio density functional calculations. We find that (i) the system comprising only nonmagnetic elements (Al, Si, O, and K) can indeed exhibit ferromagnetism, (ii) the host cage makes a confining quantum-well potential in which superatom s - and p -like states are formed, the latter p states are responsible for the spin polarization, and (iii) the size of the magnetic moment depends sensitively on atomic positions of potassium clusters. We show that the spin polarization can be described systematically in terms of the confining potential and the crystal-field splitting in the superatom p states. © 2009 The American Physical Society.

    DOI: 10.1103/PhysRevB.80.220410

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  • Ab initio derivation of the low-energy model for alkali-cluster-loaded sodalites 査読有り

    Nakamura K., Koretsune T., Arita R.

    Physical Review B - Condensed Matter and Materials Physics   80 ( 17 )   2009年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    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. © 2009 The American Physical Society.

    DOI: 10.1103/PhysRevB.80.174420

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  • Combined approach of density functional theory and quantum Monte Carlo method to electron correlation in dilute magnetic semiconductors 査読有り

    Ohe J., Tomoda Y., Bulut N., Arita R., Nakamura K., Maekawa S.

    Journal of the Physical Society of Japan   78 ( 8 )   2009年08月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present a realistic study for electronic and magnetic properties in dilute magnetic semiconductor (Ga,Mn)As. A multi-orbital Haldane-Anderson model parameterized by density-functional calculations is presented and solved with the Hirsch-Fye quantum Monte Carlo algorithm. Results well reproduce experimental results in the dilute limit. When the chemical potential is located between the top of the valence band and an impurity bound state, a long-range ferromagnetic correlations between the impurities, mediated by antiferromagnetic impurity-host couplings, are drastically developed. We observe an anisotropic character in local density of states at the impurity-bound-state energy, which is consistent with the STM measurements. The presented combined approach thus offers a firm starting point for realistic calculations of the various family of dilute magnetic semiconductors. © 2009 The Physical Society of Japan.

    DOI: 10.1143/JPSJ.78.083703

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  • Ab initio derivation of low-energy model for κ-ET type organic conductors 査読有り

    Nakamura K., Yoshimoto Y., Kosugi T., Arita R., Imada M.

    Journal of the Physical Society of Japan   78 ( 8 )   2009年08月

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    担当区分:筆頭著者   記述言語:英語   掲載種別:研究論文(学術雑誌)

    We derive effective Hubbard-type Hamiltonians of κ-(BEDT-TTF)2X, using an ab initio downfolding technique, for the first time for organic conductors. They contain dispersions of the highest occupied Wannier-type molecular orbitals with the nearest neighbor transfer t ∼ 0:067 eV for a metal X - Cu(NCS)2and 0.055 eV for a Mott insulator X - Cu2(CN)3, as well as screened Coulomb interactions. It shows unexpected differences from the conventional extended Hückel results, especially much stronger onsite interaction U ∼ 0:8eV (U/t ∼ 12{15) than the Hückel estimates (U/t ∼ 7{8) as well as an appreciable longer-ranged interaction. Reexamination on physics of this family of materials is required from this realistic basis. © 2009 The Physical Society of Japan.

    DOI: 10.1143/JPSJ.78.083710

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  • Ab initio derivation of low-energy model for iron-based superconductors LaFeAsO and LaFePO 査読有り

    Nakamura K., Arita R., Imada M.

    Journal of the Physical Society of Japan   77 ( 9 )   2008年09月

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    担当区分:筆頭著者   記述言語:英語   掲載種別:研究論文(学術雑誌)

    Effective Hamiltonians for LaFeAsO and LaFePO are derived from the downfolding scheme based on first-principles calculations and provide insights for newly discovered superconductors in the family of LnFeAsO1-xFx, Ln = La, Ce, Pr, Nd, Sm, and Gd. Extended Hubbard Hamiltonians for five maximally localized Wannier orbitals per Fe are constructed dominantly from five-fold degenerate iron-3d bands. They contain parameters for effective Coulomb and exchange interactions screened by the polarization of other electrons away from the Fermi level. The onsite Coulomb interaction estimated as 2.2 - 3.3 eV is compared with the transfer integrals between the nearest-neighbor Fe-3d Wannier orbitals, 0.2 -0.3 eV, indicating moderately strong electron correlation. The Hund's rule coupling is found to be 0.3- 0.6 eV. The derived model offers a firm basis for further studies on physics of this family of materials. The effective models for As and P compounds turn out to have very similar screened interactions with slightly narrower bandwidth for the As compound. ©2008 The Physical Society of Japan.

    DOI: 10.1143/JPSJ.77.093711

    Kyutacar

    Scopus

    その他リンク: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=54349109122&origin=inward

  • Optical absorption study by ab initio downfolding approach: Application to GaAs 査読有り

    Nakamura K., Yoshimoto Y., Arita R., Tsuneyuki S., Imada M.

    Physical Review B - Condensed Matter and Materials Physics   77 ( 19 )   2008年05月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We examine whether the essence and quantitative aspects of electronic excitation spectra are correctly captured by an effective low-energy model constructed from an ab initio downfolding scheme. A global electronic structure is first calculated by ab initio density-functional calculations with the generalized gradient approximation. With the help of constrained density-functional theory, the low-energy effective Hamiltonian for bands near the Fermi level is constructed by the downfolding procedure in the basis of maximally localized Wannier functions. The excited states of this low-energy effective Hamiltonian ascribed to an extended Hubbard model are calculated by using a low-energy solver. As the solver, we employ the Hartree-Fock approximation supplemented by the single-excitation configuration-interaction method considering electron-hole interactions. The present three-stage method is applied to GaAs, where eight bands are retained in the effective model after the downfolding. The resulting spectra well reproduce the experimental results, which indicate that our downfolding scheme offers a satisfactory framework of the electronic-structure calculation, particularly for the excitations and dynamics as well as for the ground state. © 2008 The American Physical Society.

    DOI: 10.1103/PhysRevB.77.195126

    Scopus

    その他リンク: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=44449157251&origin=inward

  • First-principles calculation of effective onsite Coulomb interactions of 3d transition metals: Constrained local density functional approach with maximally localized Wannier functions 査読有り

    Nakamura K., Arita R., Yoshimoto Y., Tsuneyuki S.

    Physical Review B - Condensed Matter and Materials Physics   74 ( 23 )   2006年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    We present an ab initio method for calculating effective onsite Coulomb interactions of solid. The method is based on constrained local density functional theory formulated in terms of maximally localized Wannier functions. This scheme can be implemented with any basis, and thus allows us to perform the constrained calculation with plane-wave-based electronic-structure codes. We apply the developed method to the evaluation of the onsite interaction of 3 d transition-metal series. The results are discussed using a heuristic formula for screened Coulomb interactions. © 2006 The American Physical Society.

    DOI: 10.1103/PhysRevB.74.235113

    Scopus

    その他リンク: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=33845803184&origin=inward

  • Effect of through-space electron transfer on infrared spectrum of amorphous selenium 査読有り

    Nakamura K., Tsuneyuki S.

    Journal of Chemical Physics   122 ( 19 )   2005年05月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    In this paper we present theoretical analyses on an infrared (IR) spectrum of amorphous selenium. The system is described by a 216-atom-chain model, and a set of molecular-dynamics simulations is performed to generate vitreous structures and vibrational modes. To describe an electronic structure of the system we employ a complete neglect of differential overlap model parametrized by ab initio cluster calculations. An IR intensity is evaluated with the Berry-phase formula for an electronic polarization. The effect of the through-space electron transfer on the IR spectrum is studied by artificially changing the magnitude of matrix elements associated with the electron transfer between nonbonded atoms in the chain. We find that the through-space electron transfer leads to (i) the enhancement of the bending IR peak at 135 cm-1 and (ii) the appearance of a new low-frequency peak around 50 cm-1, thus resulting in a good agreement with the experiment. The mechanism is discussed by a simple dipole model. © 2005 American Institute of Physics.

    DOI: 10.1063/1.1898217

    Scopus

    その他リンク: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=21544450568&origin=inward

  • Development and motion analysis of a cleaner robot for vertical type air conditioning duct 査読有り

    Yamamoto M., Hayashi Y., Nakamura K., Mohri A.

    Nihon Kikai Gakkai Ronbunshu, C Hen/Transactions of the Japan Society of Mechanical Engineers, Part C   71 ( 5 )   1704 - 1710   2005年05月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    This paper presents development and motion analysis of a cleaner robot for vertical type air conditioning duct. The air conditioning duct is used for ventilation and air conditioning. After years use of the duct without cleaning, much dust is accumulated inside the duct. That leads scattering the dust into rooms. This is not desirable in the view point of sanitation and health. Thus, periodic cleaning of the duct is requested. For the cleaning work, an air hose type cleaner robot is developed. An air nozzle is attached with the tip of the hose type robot. Compressed air blows off the dust from the air nozzle, then the dust inside the duct is collected by a dust collector with a filter. The part of nozzle is manipulated by wires' constraint using two DC motors. By watching TV monitor which shows inside of the duct, the cleaning work is done remotely using a control stick operation. To control the nozzle of the hose robot, the paper discusses a relation between position of nozzle (tip of hose robot) and wire's length. Discussions on wire force for the position is also given. An experiment of the motion for the hose robot is presented, then theoretical solutions and experimental results are compared.

    Scopus

    その他リンク: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=23144453271&origin=inward

  • Medium-range order in amorphous selenium: Molecular dynamics simulations 査読有り 国際誌

    Nakamura K., Ikawa A.

    Physical Review B - Condensed Matter and Materials Physics   67 ( 10 )   1042031 - 10420312   2003年03月

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    担当区分:筆頭著者   記述言語:英語   掲載種別:研究論文(学術雑誌)

    In this paper we present a theoretical study on a glassy structure and infrared (IR)/Raman spectra of amorphous selenium (a-Se). The vibrational spectra are calculated for two-hundred independent amorphous samples obtained by performing molecular-dynamics (MD) simulations for one linear chain of 216 Se atoms. The interaction potential used in the MD simulation is constructed on the basis of ab initio molecular-orbital calculations (with the Hartree-Fock and second-order Møller-Placed methods) for various Se clusters. The parameters in the bond-current and bond-polarizability models needed for the spectral calculations are also determined by the same ab initio approach. The calculated static structure factor, vibrational density of states, and IR/Raman spectra well reproduce experimental results. It is found that there exists a remarkable medium-range order in the disordered Se chain; i.e., a chain segment having four consecutive dihedral angles with alternate signs [i.e., (+, -, +, -) or (-, +, -, +)] tends to be excluded from the chain structure, which is attributed to the steric hindrance effect existing in those configurations. By comparing the polarized Raman spectra for two different random chains with and without the above steric hindrance effect, we find that only the former spectrum exhibits a distinct peak at 80 cm-1which is observed also in the experiment. Therefore the appearance of this peak provides useful information on the medium-range order existing in the disordered Se chain.

    Scopus

    その他リンク: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=0038417038&origin=inward

  • Vibrational properties of a regular helical Se chain 査読有り

    Nakamura K., Ikawa A.

    Physical Review B - Condensed Matter and Materials Physics   66 ( 2 )   243061 - 2430613   2002年07月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    In this paper we calculated the phonon dispersion curves and the infrared (IR)/Raman spectra of an infinite regular helical selenium (Se) chain. The ingredients needed for their calculations, i.e., the force constant matrix, dynamical-charge tensor (DCT), and polarizability-derivative tensor (PDT), were obtained from ab initio molecular orbital calculations with the second-order Møller-Plesset perturbation theory for a Se chain with finite length. Assignments for the IR and Raman spectra were performed in terms of a rotational angle τ of the helix; i.e., the phonon modes with wave number Q=0 or τ are IR active, while the phonon modes with Q=0, τ, or 2τ are Raman active. Therefore, IR and Raman spectroscopy are useful, not only for identifying the static structure but also for deriving the phonon dispersions of the Se chain. From analyses based on a valence force field model, we found that the ab initio phonon dispersion curve of the stretching band strongly depends on the off-diagonal couplings in the force constant matrix and on the chain geometry, especially the bond angle. The ab initio DCT and PDT were also analyzed with the so-called bond-current and bond-polarizability models, respectively. We found that these simple models reproduce the ab initio IR/Raman intensities quite accurately.

    DOI: 10.1103/PhysRevB.66.024306

    Scopus

    その他リンク: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=4644240669&origin=inward

  • Microscopic understanding of vibrational spectra of amorphous selenium 査読有り

    Nakamura K., Ikawa A.

    Journal of Non-Crystalline Solids   312 ( 314 )   168 - 171   2002年01月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    A chain model based on ab initio molecular orbital (MO) calculations was used to study the vibrational spectra of amorphous selenium (Se). The Infrared (IR) and Raman spectra of amorphous selenium were calculated for atomic structures obtained by classical molecular dynamics simulations. The phonon dispersion of a regular helical Se chain was used to explain the relative position between the main IR and polarized Raman peaks in the stretching band.

    DOI: 10.1016/S0022-3093(02)01680-0

    Scopus

    その他リンク: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=0036788895&origin=inward

  • Infrared absorption in amorphous selenium 査読有り

    Nakamura K., Ikawa A.

    Computer Physics Communications   142 ( 1-3 )   295 - 299   2001年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    The infrared (IR) absorption spectrum of amorphous selenium (a-Se) are calculated for the atomic structure constructed by a molecular dynamics with recently proposed chain model using an semiempirical electronic structure calculation. Its microscopic mechanism is investigated with an IR formula for chains in terms of bond and induced current correlations. The stretching band in the IR spectrum has two peaks, which are related to the intermediate range order that dihedral angle sequences with the signs of (+,-,+,-) and (-,+,-,+) hardly occur due to steric hindrance. The result urges us to modify the conventional picture that a-Se consists of the polymer chains with completely random sequences of the signs of the dihedral angles. © 2001 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0010-4655(01)00364-2

    Scopus

    その他リンク: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=0035892835&origin=inward

  • Interchain interaction in semiconducting liquid and amorphous selenium 査読有り

    Nakamura K., Ikawa A.

    Progress of Theoretical Physics Supplement   ( 138 )   266 - 267   2000年01月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)

    Atomic and electronic structures of semiconducting liquid and amorphous selenium are studied with a chain model including an anisotropic interaction between the Se atoms due to the p-lone pair on each atom.

    DOI: 10.1143/PTPS.138.266

    Scopus

    その他リンク: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=0034337296&origin=inward

▼全件表示

口頭発表・ポスター発表等

  • USPEXによる非経験的新物質探索: 水素化物への応用

    中村 和磨, 飯久保智

    日本物理学会講演概要集 

     詳細を見る

    開催期間: 2018年03月22日 - 2018年03月25日   記述言語:日本語  

    USPEXを用いた非経験的物質構造探索の研究結果について報告する。USPEXは遺伝アルゴリズムに基づき,結晶系・表面系・複雑分子の構造探索などに幅広く利用されている。第一原理計算・古典分子動力学計算など多くの汎用ソフトをサポートしており,量子力学的精度を必要とする系から大規模複雑系まで柔軟に対応できる。本研究では,第一原理電子構造ソフトVASPとUSPEXの併用による水素吸蔵合金の物質探索について報告する。

  • 幾何学的フラストレート系イリジウム酸化物Ca5Ir3O12の輸送特性

    松平 和之, 安國 友貴, 岡 知春, 分島 亮, 日夏 幸雄, 中村 和磨, 吉本 芳英, 長谷川 巧, 廣井 善二

    日本物理学会講演概要集 

     詳細を見る

    開催期間: 2017年01月   記述言語:英語  

    イリジウム酸化物Ca5Ir3O12はIrが+4.67と中間価数状態にあり,IrO6の1次元的な辺共有からなる1次元鎖が三角格子をなした幾何学的にフラストレートした強相関5d電子系物質である。今回,Caサイトの元素置換によるIrサイトへのキャリアドープ(電子ドープおよびホールドープ)した電気抵抗および熱電能におけるキャリアドープ効果について報告する。また,最近得られた単結晶試料の輸送特性などについても報告する。

    CiNii Article

  • 幾何学的フラストレート系イリジウム酸化物Ca5Ir3O12のキャリアドープ効果

    安國 友貴, 福岡 亮祐, 前田 賢, 分島 亮, 日夏 幸雄, 中村 和磨, 吉本 芳英, 松平 和之

    日本物理学会講演概要集 

     詳細を見る

    開催期間: 2016年01月   記述言語:英語  

    イリジウム酸化物 Ca5Ir3O12 (六方晶)はIrイオンの価数が+4.67と中間価数状態にあり,IrO6の辺共有からなる1次元鎖が三角格子をなした幾何学的にフラストレートした強相関5d電子系物質である。今回,CaサイトのBiおよび La 置換によるIrサイトへのキャリアドープ(電子ドープ)を行った。磁化,電気抵抗および熱電能におけるキャリアドープ効果について報告する。

    CiNii Article

  • (x)TAPPおよびpost-TAPPコードを用いた超伝導パラメータ評価

    中村 和磨, 野原 善郎, 是常隆, 吉本 芳英

    日本物理学会講演概要集 

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    開催期間: 2016年01月   記述言語:日本語  

    <p>第一原理計算汎用コード「TAPP(東京大学 ab initio program package)」および「ポストTAPP」コードを用いた最近の進捗として, 超伝導転移温度パラメータの評価を実装した。計算アルゴリズムおよびコードの紹介と実証研究に関する結果報告を行う。</p>

    CiNii Article

  • 第一原理GW+cumulant 展開法を用いた物質のスペクトル関数計算

    中村和磨, 野原善郎, 吉本芳英, 野村悠祐

    日本物理学会講演概要集 

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    開催期間: 2015年09月17日 - 2015年09月20日   記述言語:日本語  

作品

  • 第一原理多体摂動計算ソフトウェア: RESPACK

    2017年10月20日

講演

  • Ca5Ir3O12の第一原理計算

    新学術領域 J-Physics: 多極子伝導系の物理 J-Physics 地域研究会―北九州―  2019年06月 

     詳細を見る

    発表言語:日本語   講演種別:特別講演  

  • RESPACK: Ab initio software for many-body perturbation calculation and effective-model derivation

    International Conference on Frontiers of Correlated Electron Sciences  2019年05月 

     詳細を見る

    発表言語:英語   講演種別:招待講演  

  • 第一原理多体摂動論ソフトウェアRESPACKの開発と公開

    物性研究所スパコン共同利用・ CCMS合同研究会「計算物質科学の新展開」  2019年04月 

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    発表言語:日本語   講演種別:招待講演  

  • CCMSハンズオン: RESPACK講習会

    TIA “かけはし” 連携講座( 東京大学柏フューチャーセンター )  2019年03月 

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    発表言語:日本語   講演種別:特別講演  

  • CCMSハンズオン: RESPACK講習会

    TIA “かけはし” 連携講座  2017年12月 

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    講演種別:特別講演  

  • Search for new material structure using USPEX

    7th Annual World Congress of Nano Science & Technology-2017  2017年10月 

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    講演種別:招待講演  

  • 第一原理計算を用いた超伝導物性研究

    応用物理学会超伝導分科会第53回研究会「新奇超伝導の進展」  2016年06月 

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    講演種別:招待講演  

  • 第一原理からの物質の低エネルギー有効模型構築: constrained RPA and constrained GW

    トポロジカル物性と計算物質科学が創出する新物質科学に関する研究会  2016年03月 

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    講演種別:招待講演   開催地:東京大学物性研究所  

  • 第一原理多体摂動計算を用いた物性研究

    物性研究所短期研究会「量子物質研究の最前線」  2015年12月 

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    講演種別:招待講演   開催地:東京大学物性研究所  

  • 強相関金属の第一原理多体摂動計算

    第一原理多体摂動論ワークショップ―多体摂動計算手法の現状と展望  2015年08月 

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    講演種別:招待講演   開催地:東京大学柏フューチャーセンター  

  • 第一原理多体摂動論の前線

    日本物理学会第70回年次大会(2015年)  2015年03月 

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    講演種別:招待講演   開催地:早稲田大学  

  • 金属系の第一原理多体摂動計算

    実験と計算科学の協奏が拓く物質科学・物質開発のフロンティア―超伝導とトポロジカル物質の新展開  2015年03月 

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    講演種別:招待講演   開催地:東京大学理学部  

  • Recent progress in ab initio many-body perturbation theory for correlated materials

    International Workshop on New Frontier of Numerical Methods for Many-Body Correlation  2015年02月 

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    講演種別:招待講演   開催地:The University of Tokyo  

  • 21pAJ-3 第一原理多体摂動論の前線

    日本物理学会講演概要集  2015年01月 

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    開催期間: 2015年01月   発表言語:日本語   講演種別:特別講演  

    CiNii Article

  • Ab initio GW analysis for low-energy plasmaron states

    The 2nd International Symposium on Computics: Quantum Simulation and Design  2014年12月 

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    講演種別:招待講演   開催地:The University of Tokyo  

  • TAPP-GWコード開発の進捗

    xTAPP Developers Meeting 2014  2014年08月 

     詳細を見る

    講演種別:招待講演   開催地:東京大学理学部  

  • 低エネルギープラズモン状態のGW解析:有機導体および遷移金属酸化物への応用

    フロンティア物理講演会 in 山形  2014年01月 

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    講演種別:招待講演   開催地:山形大学理学部  

  • 低エネルギープラズマロン状態のGW解析

    第3回強相関電子系理論の最前線―若手によるオープン・イノベーション  2013年12月 

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    講演種別:招待講演   開催地:勝浦観光ホテル  

  • Effective model from first principles

    PGI-1 Seminar, Jülich  2012年02月 

     詳細を見る

    講演種別:招待講演   開催地:Juelich FORSCHUNGSZENTRUM, Germany  

  • The G0 dependence of low-energy model: GGA, Hartree, Hartee-Fock starting points

    JST-CREST program “High-accuracy hierarchical and many-body schemes for materials simulations”  2012年01月 

     詳細を見る

    講演種別:招待講演   開催地:Ecole Polytechnique, France  

  • Ab initio Derivation of Correlated Superatom Model for Potassium Loaded Zeolite A

    16th International Symposium on Intercalation Compounds  2011年03月 

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    講演種別:招待講演   開催地:Seč-Ústupky, Czech Republic  

  • Ab initio Low-Dimensional Physics Opened Up by Constrained RPA for Energy and Space: Applications to LaFeAsO and \kappa-(BEDT-TTF)2X

    Seminars at Center for Computational Materials Science, Vienna Technical University  2011年02月 

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    講演種別:招待講演   開催地:The international House of Japan, Minato-ku Tokyo  

▼全件表示

報道関係

  • 水銀系銅酸化物超伝導体の超伝導転移温度が上昇するメカニズムを解明   その他

    美藤正樹, 中村和磨, 出口博之, 他10名

    プレスリリース  2017年02月08日

  • 〜超伝導転移温度上昇への新たな道筋を開拓〜 レ二ウム金属の超伝導転移温度が“せん断ひずみ”によって飛躍的に上昇するメカニズムを解明   その他

    美藤正樹, 中村和磨, 出口博之, 他9名

    プレスリリース  2016年11月04日

学術関係受賞

  • 日本物理学会第23回論文賞

    日本物理学会   2018年03月24日

    中村和磨, 三宅隆, 有田亮太郎, 今田正俊

     詳細を見る

    受賞国:日本国

科研費獲得実績

  • スピン軌道結合系イリジウム酸化物の逐次新奇相転移と電流誘起交差相関物性の解明

    研究課題番号:22H01183  2022年04月 - 2026年03月   基盤研究(B)

  • 熱力学状態図の第一原理計算-水素化物状態図作成と圧力・組成・温度特性評価-

    研究課題番号:19K03673  2019年04月 - 2022年03月   基盤研究(C)

  • 強相関電子材料のドメイン界面におけるハイブリッド配位環境を利用した機能性制御

    研究課題番号:17H03393  2017年04月 - 2020年03月   基盤研究(B)

  • ランタノイド系希土類強磁性元素の超高圧磁性の全貌解明

    研究課題番号:17H03379  2017年04月 - 2020年03月   基盤研究(B)

  • 強相関物質設計と機能開拓ー非平衡系・非周期系への挑戦ー

    研究課題番号:16H06345  2016年04月 - 2021年03月   基盤研究(S)

  • 第一原理エリアシュベルグ計算コード開発と実証研究

    研究課題番号:16K05452  2016年04月 - 2020年03月   基盤研究(C)

  • 第一原理GW計算を用いた低密度キャリア系の電子構造研究

    研究課題番号:25800200  2013年04月 - 2017年03月   若手研究(B)

  • 超伝導転移温度の第一原理計算法の開発と応用

    研究課題番号:23340095  2011年11月 - 2014年03月   基盤研究(B)

  • 鎖状分子を基本構造とするTeナノ粒子の階層構造と光学特性

    研究課題番号:23510120  2011年04月 - 2014年03月   基盤研究(C)

  • 有機化合物強相関電子系に対する第一原理有効模型構築:『物質差異』の定量化

    研究課題番号:23110708  2011年04月 - 2013年03月   新学術領域研究

  • 第一原理有効模型と相関科学のフロンティア

    研究課題番号:22104010  2010年04月 - 2015年03月   新学術領域研究

  • 物質の低エネルギー有効模型の第一原理導出とこれを用いた実証研究

    研究課題番号:22740215  2010年04月 - 2013年03月   若手研究(B)

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受託研究・共同研究実施実績

  • 第一原理有効模型導出プログラムRESPACKと模型解析プログラムHΦ/mVMCの融合による非経験的強相関電子構造解析ソフトウェアの整備

    2018年04月 - 現在

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    研究区分:その他共同研究等

    2018年度東京大学物性研究所ソフトウェア開発・高度化プロジェクトの対称プログラムとしてRESPACKが採択された。

その他研究活動

  • 計算と実験の連携に基づく材料科学研究基盤構築 ―遷移金属酸化物デバイス機能開拓―

    2022年04月
    -
    2024年03月

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    本申請課題では, 遷移金属酸化物の物性・機能開拓およびデバイス応用のための基礎知見蓄積を目的として, (1) 銅酸化物に対する高圧巨大ひずみ加工による構造・電子物性調査, (2) 遷移金属酸化物人工超格子の界面物性理解に向けて取り組む。材料特有の問題である格子欠陥・転位に対する電子論的理解を得るため, 第一原理計算, 合成・加工・材料評価, 物性測定の観点から連携して研究を行う。現在の物質科学は, 計算と実験の高度連携が必要とされ, チーム最大成果が求められる状況になっている。本学の特色あるシーズを起点とすることで対外的な研究上の優位をより一層高め, 様々な研究課題に協働・迅速に取り組める研究協力体制を構築する。

  • i-ENERON 環境エネルギー融合研究センター

    2021年04月
    -
    現在

  • 巨大ひずみによって創出される励起状態を利用した電子物性開拓

    2021年04月
    -
    2022年03月

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    金属材料やセラミック材料に巨大ひずみを注入し、結晶構造が励起された状態(エキサイト格子状態と命名)を創出し、そこで創出される新たな電子状態を利用し、磁性材料・超伝導体材料・半導体材料の開発を目指している。昨年度、包括的研究については、大型外部資金獲得に挑戦し、不採択という結果に終わった。本研究プロジェクトは、その中の超伝導体・金属材料を通じて、エキサイト格子状態が発現する新規物理現象に関する研究を継続し、本研究課題がより多くの研究者を巻き込む舞台になるように研究基盤を強固なものにする。

  • 平成29年度研究力強化事業 (交差相関物性を利用した高効率環境発電材料による次世代自立型電源の開発)

    2017年04月
    -
    2018年03月

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    本学の材料開発,デバイス作成,電源製作の3つのグループによって構成された研究組織を立ち上げ(全6名),材料開発からデバイス作成および電源製作までのプロセスを統合的に行い,自立型電源システム構築を目的とした学内プロジェクトを立ち上げ,研究を行った。

  • 平成28年度大学改革プロジェクト事業 (次世代物質・材料開発手法の戦略的研究)

    2016年04月
    -
    2017年03月

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    第一原理計算や高度分析技術,AI技術等に知見のある本学研究者 7 名が協同して,次世代物質・材料開発に関して最新の知見を取り込んだ独自の開発手法を構築することを目指して学内プロジェクトを立ち上げ,研究を推進した。

  • 戦略的研究ユニット化促進プロジェクト (高温超伝導体のさらなる転移温度向上を目指した物質設計ユニット)

    2015年04月
    -
    2021年03月

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    高温超伝導体のさらなる転移温度向上を目指した物質設計ユニットを本学の教員8名より形成し,学内プロジェクトとして研究を行っている。

  • 九州工業大学物性グループセミナー

    2013年05月
    -
    現在

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    2013年5月より九州工業大学物性グループセミナーを組織して定期的にセミナーを開催している。本学の18名の教員が参加している。2018年3月までに38回のセミナーを開催している。これらのセミナーを通した本学教員の交流により、共同研究、科研費の共同提出、学内プロジェクトへの共同提出(三件採択)に繋がっている。

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担当授業科目(学内)

  • 2023年度   固体物理学特論

  • 2023年度   量子力学

  • 2023年度   基礎量子力学

  • 2023年度   物理学ⅡB

  • 2023年度   物理学ⅡA

  • 2023年度   物理学Ⅰ

  • 2022年度   固体物理学特論

  • 2022年度   量子力学

  • 2022年度   基礎量子力学

  • 2022年度   物理学ⅡB

  • 2022年度   物理学Ⅰ

  • 2021年度   固体物理学特論

  • 2021年度   量子力学

  • 2021年度   基礎量子力学

  • 2021年度   物理学Ⅰ

  • 2020年度   固体物理学特論

  • 2020年度   物理学ⅡB

  • 2020年度   物理学ⅡA

  • 2020年度   物理学Ⅰ

  • 2019年度   固体物理学特論

  • 2019年度   物理学ⅡB

  • 2019年度   物理学ⅡA

  • 2019年度   物理学Ⅰ

  • 2018年度   固体物理学特論

  • 2018年度   物理学ⅡA

  • 2018年度   物理学ⅡB

  • 2018年度   物理学ⅡB

  • 2018年度   物理学Ⅰ

  • 2017年度   固体物理学特論

  • 2017年度   物理学ⅡB

  • 2017年度   物理学ⅡA

  • 2017年度   物理学Ⅰ

  • 2016年度   物理学ⅡB

  • 2016年度   物理学ⅡA

  • 2016年度   物理学Ⅰ

  • 2016年度   固体物理学特論

  • 2015年度   固体物理学特論Ⅰ

  • 2015年度   固体物理学特論Ⅱ

  • 2015年度   物理学Ⅰ

  • 2015年度   物理学ⅡA

  • 2015年度   物理学ⅡB

  • 2014年度   物理学Ⅰ

  • 2014年度   力学基礎

  • 2014年度   固体物理学特論

  • 2014年度   基礎量子力学

  • 2014年度   物理学ⅡA

  • 2013年度   固体物理学特論

  • 2013年度   基礎量子力学

  • 2013年度   物理学ⅡA

  • 2013年度   物理学Ⅰ

  • 2013年度   物理学Ⅰ

  • 2012年度   基礎量子力学

  • 2012年度   基礎量子力学

  • 2012年度   物理学ⅡA

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教育活動に関する受賞・指導学生の受賞など

  • 2017年度前期科目総合システム工学科授業アンケート優秀賞

    九州工業大学総合システム工学科  

    2017年08月17日

    中村和磨

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    総合システム工学科生対象の授業アンケート集計で、中村が担当する物理学Ⅰが優秀賞となった。

その他教育活動

  • 他大学集中講義 (山形大学理学部/理学系大学院 「多体摂動論」)

    2015年09月
    -
    2015年10月

学会・委員会等活動

  • 日本物理学会   2018年秋季大会領域11セッション(11aM301)座長  

    2018年09月

  • 日本物理学会   第73回年次大会(2018年)領域11セッション(22pK704)座長  

    2018年03月

  • 日本物理学会   2017年秋季大会領域11セッション(22aJ24)座長  

    2017年09月

  • 日本物理学会   2016年秋季大会領域11セッション(13pAE)座長  

    2016年09月

  • 日本物理学会   2014年秋季大会領域8セッション(8pBK)座長  

    2014年09月

  • 日本物理学会   2013年秋季大会領域7セッション(27oDJ)座長  

    2013年09月

  • 日本物理学会   2013年秋季大会領域8セッション(27aED)座長  

    2013年09月

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