Itinerant-Localized Duality Picture of Spin Fluctuations in High-T<sub>c</sub>Cuprates. I. Nested Spin-Fluctuation Theory

Miyake, Kazumasa; Narikiyo, Osamu

doi:10.1143/jpsj.63.3821

Cited by 82 publications

(47 citation statements)

References 57 publications

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“…The antiferromagnetic spin fluctuations described by χ s (q, iΩ n ) play a dominant role in the FLEX approximation. The characteristic results of the nearly anti-ferromagnetic Fermi liquid theory 17,53,54,55,56,59,60,72,73,75) are qualitatively reproduced within the FLEX approximation. The superconducting critical temperature T c is determined as the temperature below which the linearized Dyson-Gor'kov equation has a non-trivial solution ( Fig.…”

Section: §1 Introductionmentioning

confidence: 76%

Pseudogap Phenomena and Superconducting Fluctuations in Hubbard Model for High-T_cCuprates

2001

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The pseudogap phenomena in High-Tc cuprates are investigated on the basis of the Hubbard model which includes only the on-site repulsive interaction U . We consider the pairing scenario for the pseudogap. The pseudogap arises from the resonance scattering due to the strong superconducting fluctuations. First, the electronic state and the anti-ferromagnetic spin fluctuations are calculated by using the fluctuation exchange (FLEX) approximation. The T-matrix which is the propagator of the superconducting fluctuations is calculated by extending theÉliashberg equation. The characteristics of the superconducting fluctuations due to the pairing interaction arising from the spin fluctuations are represented in the T-matrix. The self-energy due to the superconducting fluctuations is calculated by the T-matrix approximation. The pseudogap is shown in the single particle properties and the magnetic properties. Moreover, a comprehensive explanation of the doping dependence of the pseudogap is obtained. Furthermore, we apply the theory to the electron-doped cuprates and obtain the consistent results with the recent experiments. Finally, the self-consistent calculation for the spin fluctuations, superconducting fluctuations and the single particle properties are carried out within the FLEX and the self-consistent T-matrix approximations. The relation between the superconducting fluctuations and the spin fluctuations are clarified. The calculated superconducting critical temperature Tc is remarkably reduced from the results of the mean field (FLEX) calculation. In particular, it is shown that the critical temperature decreases with decreasing doping in the under-doped region with large U . The pseudogap phenomena in under-doped High-T c cuprates have been interested for many years. The pseudogap is considered to be a key issue for the comprehensive understanding of the High-T c superconductivity.The pseudogap phenomena mean the suppression of the spectral weight above T c without any long range order. They are universal phenomena observed in various compounds of High-T c cuprates in the under-doped region. First, the pseudogap was found in the magnetic excitation channel by the nuclear magnetic resonance (NMR) experiment. 1) At present, the pseudogap phenomena have been observed in various quantities which include NMR, 1, 2, 3, 4, 5, 6, 7) neutron scattering, 8) transport, 9, 10) optical spectrum, 11) electronic specific heat, 12) density of states 13) and the single particle spectral weight. 14) The experimental results are reviewed in ref. 15.There are many theoretical scenarios proposed for the pseudogap phenomena. An important one is the resonating valence bond (RVB) theory. The RVB theory is an approach from the non-Fermi liquid state and attributes the pseudogap to the singlet pairing of the spinons. 16) As an approach from the Fermi liquid state, the magnetic * E-mail: yanase@hosi.phys.s.u-tokyo.ac.jp * * Present address: Department of Physics, University of Tokyo, Tokyo 113-0033 scenario has been investigated. 17,18) ...

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Section: §1 Introductionmentioning

confidence: 76%

Pseudogap Phenomena and Superconducting Fluctuations in Hubbard Model for High-T_cCuprates

2001

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“…In actual, many possible mechanisms of pseudogaps have already been proposed along these scenarios. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Since cuprateoxide superconductors are highly anisotropic quasi-twodimensional ones, it is also a reasonable argument that, even if either of these scenarios is relevant, low dimensionality must play a crucial role. If a second-order phase transition occurred at a nonzero critical temperature T c in one or two dimensions, eventual effects of critical thermal fluctuations or their integrated effects over the wave-number space would diverge at the nonzero T c .…”

Section: Introductionmentioning

confidence: 99%

Opening of a pseudogap in a quasi-two-dimensional superconductor due to critical thermal fluctuations

Ohkawa

2006

Phys. Rev. B

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We examine the role of the anisotropy of superconducting critical thermal fluctuations in the opening of a pseudogap in a quasi-two-dimensional superconductor such as a cuprate-oxide high-temperature superconductor. When the anisotropy between planes and their perpendicular axis is large enough and its superconducting critical temperature T c is high enough, the fluctuations are much developed in the critical region so that lifetime widths of quasiparticles are large and the energy dependence of the self-energy deviates from that of Landau's normal Fermi liquids. A pseudogap opens in such a critical region because quasiparticle spectra around the chemical potential are swept away due to the large lifetime widths. The pseudogap never smoothly evolves into a superconducting gap; it starts to open at a temperature higher than T c while the superconducting gap starts to open just at T c . When T c is rather low but the ratio of G ͑0͒ / k B T c , with G ͑0͒ the superconducting gap at T = 0 K, is much larger than a value of about 4 according to the mean-field theory, the pseudogap must be closing as temperature T approaches to the low T c because thermal fluctuations become less developed as T decreases. Critical thermal fluctuations cannot cause the opening of a prominent pseudogap in an almost isotropic three-dimensional superconductor, even if its T c is high.

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“…12 Actually, ρ and S of NaCo 2 O 4 are qualitatively consistent with some theories for high-T c superconductors. 13,14 In particular, ρ of Na 1.1−x Ca x Co 2 O 4 can be explained by adjusting the parameters in Ref. 13.…”

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confidence: 99%

Na-site substitution effects on the thermoelectric properties ofNaCo2O4

et al. 1999

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The resistivity and thermopower of Na1+xCo2O4 and Na1.1−xCaxCo2O4 are measured and analyzed. In Na1+xCo2O4, whereas the resistivity increases with x, the thermopower is nearly independent of x. This suggests that the excess Na is unlikely to supply carriers, and decreases effective conduction paths in the sample. In Na1.1−xCaxCo2O4, the resistivity and the thermopower increase with x, and the Ca 2+ substitution for Na + reduces the majority carriers in NaCo2O4. This means that they are holes, which is consistent with the positive sign of the thermopower. Strong correlation in this compound is evidenced by the peculiar temperature dependence of the resistivity.PACS numbers: 72.15. Jf, 72.80.Ga, 72.15.LhThere appears a growing interest to a hunt for new thermoelectric (TE) materials, 1 reflecting urgent needs for a new energy-conversion system in harmony with our environments. A TE material generates electric power in the presence of temperature gradient through the Seebeck effect, and pumps heat in the presence of electric current through the Peltier effect. A serious drawback is the low conversion efficiency: It is characterized by the so-called "figure of merit" Z = S 2 /ρκ, where S, ρ and κ are the thermopower, resistivity and thermal conductivity of a TE material, respectively. In other words, a good TE material is a material that shows large S, low ρ and low κ. However, a high value of Z is difficult to realize, because the three parameters cannot be changed independently. To overcome this difficulty, a number of new concepts and new materials have been examined.Recently we have observed that a layered cobalt oxide NaCo 2 O 4 exhibits unusually large S (100 µV/K at 300 K) accompanied by low ρ (200 µΩcm at 300 K) along the direction parallel to the CoO 2 plane. 2 NaCo 2 O 4 belongs to a layered Na bronze Na x CoO 2 , which was studied as a cathode for sodium batteries. 3 During the characterization, Molenda et al. 4 first found a large S in Na 0.7 CoO 2 . Although they noticed that S was anomalously large, they did not mention a possibility for a TE material. Their samples were polycrystals, the resistivity of which was 2-4 mΩcm at 300 K, much higher than that of our crystals. Our finding is that the carrier density (n) is of the order of 10 21 − 10 22 cm −3 , and is two orders of magnitude larger than n of conventional TE materials. This is difficult to understand in the framework of a conventional one-electron picture, and may indicate a way to get a good TE material other than the conventional approach. We have proposed that strong electron-electron correlation plays an important role in the enhancement of the thermopower of NaCo 2 O 4 .Even in a correlated system, we can expect that a conductor of low n will have a large S, because the diffusive part of S is the transport entropy, of the order of k B T /E F , where E F is the Fermi energy. 5 Thus it would be tempting to improve the TE properties in NaCo 2 O 4 by decreasing n. We easily think of three ways to change n in NaCo 2 O 4 , i.e., (i) doping of e...

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Itinerant-Localized Duality Picture of Spin Fluctuations in High-T_cCuprates. I. Nested Spin-Fluctuation Theory

Cited by 82 publications

References 57 publications

Pseudogap Phenomena and Superconducting Fluctuations in Hubbard Model for High-T_cCuprates

Pseudogap Phenomena and Superconducting Fluctuations in Hubbard Model for High-T_cCuprates

Opening of a pseudogap in a quasi-two-dimensional superconductor due to critical thermal fluctuations

Na-site substitution effects on the thermoelectric properties ofNaCo2O4

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Itinerant-Localized Duality Picture of Spin Fluctuations in High-TcCuprates. I. Nested Spin-Fluctuation Theory

Cited by 82 publications

References 57 publications

Pseudogap Phenomena and Superconducting Fluctuations in Hubbard Model for High-TcCuprates

Pseudogap Phenomena and Superconducting Fluctuations in Hubbard Model for High-TcCuprates

Opening of a pseudogap in a quasi-two-dimensional superconductor due to critical thermal fluctuations

Na-site substitution effects on the thermoelectric properties ofNaCo2O4

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Product

Resources

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Itinerant-Localized Duality Picture of Spin Fluctuations in High-T_cCuprates. I. Nested Spin-Fluctuation Theory

Pseudogap Phenomena and Superconducting Fluctuations in Hubbard Model for High-T_cCuprates

Pseudogap Phenomena and Superconducting Fluctuations in Hubbard Model for High-T_cCuprates