Ab Initio MO Calculations of Effective Exchange Integrals between Transition-Metal Ions via Oxygen Dianions: Nature of the Copper-Oxygen Bonds and Superconductivity

Yamaguchi, Kizashi; Takahara, Yoichi; Fueno, Takayuki; Nasu, Keiichirō

doi:10.1143/jjap.26.l1362

Cited by 225 publications

(196 citation statements)

References 17 publications

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“…Then the magnitude of J is a measure of transition temperature for our J model of superconductivity. 71 Before the discovery of the high Tc cuprates by Bednort and Muller, 72 our UHF calculations of MOM units 39 have indicated that the magnitude of J value for the CuOCu unit is one-order larger than those of other transition metal oxides. Therefore, after the discovery of the material, we immediately presented our J-model for the high-T c superconductivity (T c = cJ, c = constant) on the basis of the spin fluctuation mechanism.…”

Section: B Superconductivity Via Spin Hamiltonian Model (I) Spin Hamentioning

confidence: 99%

“…Therefore, after the discovery of the material, we immediately presented our J-model for the high-T c superconductivity (T c = cJ, c = constant) on the basis of the spin fluctuation mechanism. 71 We have also presented possible moleculebased analogs to the high-Tc cuprates on the basis of our J model . To this end, the ab initio calculations of J values for several types of compounds have been carried out.…”

Section: B Superconductivity Via Spin Hamiltonian Model (I) Spin Hamentioning

confidence: 99%

“…On the other hand, the high-Tc cuprate superconductors are antiferromagnets before hole doping as illustrated in Figure 11 because of the metal insulator transition in the CuO2 plane via strong electron correlation. 71 The most important On the other hand, the pseudo gap is often considered to be an indication of the preformed Cooper pair before the Bose-Einstein (BE) condensation to the high-T c d-wave superconductivity (dSC). Several groups [78][79][80][81] have pointed out that the stripe shown in Figure 11 may be its origin for pseudo gap.…”

Section: B Superconductivity Via Spin Hamiltonian Model (I) Spin Hamentioning

confidence: 99%

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Spin and Pseudo Spins in Theoretical Chemistry. A Unified View for Superposed and Entangled Quantum Systems

2003

Bulletin of the Korean Chemical Society

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A unified picture for magnetism, superconductivity, quantum optics and other properties of molecule-based materials has been presented on the basis of effective model Hamiltonians, where necessary parameter values have been determined by the first principle calculations of cluster models and/or band models. These properties of the matetials are qualitatively discussed on the basis of the spin and pseudo-spin Hamiltonian models, where several quantum operators are expressed by spin variables under the two level approximation. As an example, ab initio broken-symmetry DFT calculations are performed for cyclic magnetic ring constructed of 34 hydrogen atoms in order to obtain effective exchange integrals in the spin Hamiltonian model. The natural orbital analysis of the DFT solution was performed to obtain symmetry-adapted molecular orbitals and their occupation numbers. Several chemical indices such as information entropy and unpaired electron density were calculated on the basis of the occupation numbers to elucidate the spin and pair correlations, and bonding characteristic (kinetic correlation) of this mesoscopic magnetic ring. Both classical and quantum effects for spin alignments and singlet spin-pair formations are discussed on the basis of the true spin Hamiltonian model in detail. Quantum effects are also discussed in the case of superconductivity, atom optics and quantum optics based on the pseudo spin Hamiltonian models. The coherent and squeezed states of spins, atoms and quantum field are discussed to obtain a unified picture for correlation, coherence and decoherence in future materials. Implications of theoretical results are examined in relation to recent experiments on molecule-based materials and molecular design of future molecular soft materials in the intersection area between molecular and biomolecular materials.

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Section: B Superconductivity Via Spin Hamiltonian Model (I) Spin Hamentioning

confidence: 99%

Section: B Superconductivity Via Spin Hamiltonian Model (I) Spin Hamentioning

confidence: 99%

Section: B Superconductivity Via Spin Hamiltonian Model (I) Spin Hamentioning

confidence: 99%

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Spin and Pseudo Spins in Theoretical Chemistry. A Unified View for Superposed and Entangled Quantum Systems

2003

Bulletin of the Korean Chemical Society

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“…But we could not imagine that such finding might be related to the high-T c superconductivity, because our main interest is to elucidate electronic structure and reactivity of transition metal oxides. After the discovery of high-T c cuprates by Bednorz and Mü ller [4], we immediately proposed a magnetic (magnetic excitation-mediated) model (T c ϭ cJ(k B )) [15], where J is taken as a measure of magnetic excitation. The constant c is now determined by possible microscopic models such as t-J, boson-fermion, magnon excitation, and spin fluctuation models [9 -35].…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, the magnetic model [15] in the k-space is formulated as spin fluctuation (SF) theory [9,10,28,29] and/or spin-bag theory [17,19] in the weak correlation regime. Since metallic and magnetic phases have been observed, depending on kinds of M and Pn in LaOMPn [41][42][43][44][45][46][47][48][49][50], magnetic excitation mechanisms have been received current interest in relation to the exotic superconductivity.…”

Section: Introductionmentioning

confidence: 99%

N‐bands Hubbard models. IV. Comparisons of electron‐ or hole‐doped quaternary oxypictides LaOMPn superconductors with cuprates

Yamaguchi

Yamanaka

Isobe

et al. 2008

Int J of Quantum Chemistry

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ABSTRACT:A lot of theoretical and experimental results are examined to obtain a unified picture of magnetism and superconductivity in strongly correlated electron systems. First principle computational results reported recently have been used to elucidate electronic structures of strongly correlated electron systems. In this series of articles theoretical efforts for the systems such as transition metal oxides have been extended to search high-T c superconductors (HTSC) other than cuprates in relation to possible mechanism(s) of high-T c superconductivity. Very recently, Kamihara et al. have found that quaternary oxypictides LaOMPn (M ϭ V, Cr, Mn, Fe, Co, Ni, and Pn ϭ P, As) are a new family of high-T c superconductors, exhibiting high-transition temperature T c ϭ 26 K for the case of M ϭ Fe and Pn ϭ As. Since iron has been believed to be magnetic in many systems, their finding raises extremely interesting question concerning with relationships between magnetism and superconductivity. Moreover, coexistence of antiferromagnetism (AF) and superconductivity (SC) is also discovered in the recently synthesized cuprates with five CuO 2 planes. This may indicate the uniformly mixed phase of AF and SC in cuprates without disorder corresponds to spin glass, instead of other complex phases resulting from random potentials in disordered cuprates. Coexistence of AF and SC phases and multiband effects are also suggested for quaternary oxypictides LaOMPn. Here, comparison between quaternary oxypictides LaOMPn and cuprates is carried out from both theoretical and experimental grounds, leading to an extension of our magnetic (J) model for LaOMPn. Implications of these analyses are discussed in relation to possible candidates of HTSC with multi (N)-layers consisted of iso-electronic -d, -R, and -R systems, for which similar electronic phases are expected from the theoretical grounds.

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Possibilities of charge- and/or spin-mediated superconductors and photo-induced superconductors in the intermediate region of metal-insulator transitions

Nagao

Mitani

Nishino

et al. 1997

Int. J. Quant. Chem.

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Magnetism, conductivity, and superconductivity of molecular materials are discussed on the basis of extended Hubbard᎐Peierls Hamiltonians, which involve Ž . Ž . four parameters; transfer integral T , electron-lattice interaction W , and on-site and Ž . intersite Coulomb interactions U, V . The four-component spinor is introduced to define Ž order parameters which characterize four different electronic states charge density wave, . spin density wave, singlet and triplet superconductivities in a unified fashion. Several intermediate regions in these parameters are interesting and important from current theoretical reasons. Many experimental results clearly show the importance of intermediate correlation regimes for active controls of these states by chemical modifications and by external fields such as high pressure. Several model Hamiltonians such as CT and t᎐J models are derived for elucidation of potential electronic properties of molecule-based materials. Recent computational results based on the t᎐J model are utilized to rationalize our J model for spin-mediated superconductivity. Possibilities of magnetic conductors, charge-andror spin-mediated superconductors, and photoinduced superconductors instead of the charge-mediated Little model are examined in the intermediate region of several metal᎐insulator transitions. Possible candidates are also proposed on the basis of various circumstantial experimental results. Implications of the calculated results are finally discussed in relation to the recent development of the intersection area among conducting, magnetic, and optical molecular materials.

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Ab Initio MO Calculations of Effective Exchange Integrals between Transition-Metal Ions via Oxygen Dianions: Nature of the Copper-Oxygen Bonds and Superconductivity

Cited by 225 publications

References 17 publications

Spin and Pseudo Spins in Theoretical Chemistry. A Unified View for Superposed and Entangled Quantum Systems

Spin and Pseudo Spins in Theoretical Chemistry. A Unified View for Superposed and Entangled Quantum Systems

N‐bands Hubbard models. IV. Comparisons of electron‐ or hole‐doped quaternary oxypictides LaOMPn superconductors with cuprates

Possibilities of charge- and/or spin-mediated superconductors and photo-induced superconductors in the intermediate region of metal-insulator transitions

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