Phase Diagram of Superconductivity    on the Anisotropic Triangular Lattice Hubbard Model:   An Effective Model of  <i>κ</i>-(BEDT-TTF) Salts

Kino, Hiori; Kontani, Hiroshi

doi:10.1143/jpsj.67.3691

Cited by 189 publications

(188 citation statements)

References 21 publications

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“…59,60) It has been shown that the superconducting critical temperature with a relevant order T c ∼ 100K is obtained by the FLEX approximation for High-T c cuprates. 61,62,63,64,65,66,67) The relevant results are also obtained for the organic superconductor κ-(BEDT-TTF) compounds 68,69,70) and for the ladder type compound Sr 14−x Ca x Cu 24 O 41 . 71) Moreover, the FLEX approximation is used to explain the anomalous properties resulting from the anti-ferromagnetic spin fluctuations, such as the Hall coefficient, 72, 73) the neutron resonance peak and the dip-hump structure in ARPES.…”

Section: §1 Introductionmentioning

confidence: 88%

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: 88%

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

2001

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“…What is interesting though is that the proposed scenario can give a unified approach to SC in all organic CTS, irrespective of whether the insulating state proximate to SC is AFM 102 , CO 67,103 or VBS 82 . Recall that within existing mean field theories the AFM-to-SC transition is driven by spin fluctuations [13][14][15][16][17][18][19][20][21][22][23] , while the CO-to-SC transition is driven by charge fluctuations 65 . Even if we ignore that recent precise numerical calculations [25][26][27] have demonstrated the absence of SC within the proposed spin-fluctuation models in this context (thereby raising doubts also about mean-field theory of charge-fluctuation mediated superconductivity), different mechanisms of SC for structurally related materials with identical or nearidentical molecular components appear to be unrealistic.…”

Section: Consequence Of Stronger Frustration-paired Electron Liquid Amentioning

confidence: 99%

“…An extension of the RVB theory of dopant-induced SC in ρ = 1 is the proposal that frustration-induced SC occurs in the anisotropic triangular lattice within the simple Hubbard model even for ρ exactly 1, where a narrow superconducting phase is straddled on both sides by broader PM and AFM insulator phases [13][14][15][16][17][18][19][20][21][22][23] . It has been claimed that this transition explains the SC in the CTS [13][14][15][16][17][18][19][20][21][22][23][24] . Recent numerical work by us and others, however, have determined that SC is absent within the ρ = 1 triangular lattice Hubbard model [25][26][27] and the earlier results are artifacts of mean-field approximations.…”

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confidence: 99%

Paired electron crystal: Order from frustration in the quarter-filled band

et al. 2011

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We present a study of the effects of simultaneous charge-and spin-frustration on the twodimensional strongly correlated quarter-filled band on an anisotropic triangular lattice. Our conclusions are based on exact diagonalization studies that include electron-electron interactions as well as adiabatic electron-phonon coupling terms treated self-consistently. The broken-symmetry states that dominate in the weakly frustrated region near the rectangular lattice limit are the well known antiferromagnetic state with in-phase lattice dimerization along one direction, and the Wigner crystal state with the checkerboard charge order. For moderate to strong frustration, however, the dominant phase is a novel spin-singlet paired-electron crystal (PEC), consisting of pairs of charge-rich sites separated by pairs of charge-poor sites. The PEC, with coexisting charge-order and spin-gap in two dimension, is the quarter-filled band equivalent of the valence bond solid (VBS) that can appear in the frustrated half-filled band within antiferromagnetic spin Hamiltonians. We discuss the phase diagram as a function of on-site and intersite Coulomb interactions as well as electronphonon coupling strength. We speculate that the spin-bonded pairs of the PEC can become mobile for even stronger frustration, giving rise to a paired-electron liquid. We discuss the implications of the PEC concept for understanding several classes of quarter-filled band materials that display unconventional superconductivity, focusing in particular on organic charge transfer solids. Our work points out the need to go beyond quantum spin liquid (QSL) concepts for highly frustrated organic charge-transfer solids such as κ-(BEDT-TTF)2Cu2(CN)3 and EtMe3Sb[Pd(dmit)2]2, which we believe show frustration-induced charge disproportionation at low temperatures. We discuss possible application to layered cobaltates and 1 4 -filled band spinels.

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“…In analogy to these theories, mean-field and dynamic mean-field theories of κ-(ET) 2 X have proposed that SC also occurs within the exactly 1 2 -filled band Hubbard model on an anisotropic triangular lattice, for a range of Hubbard U and anisotropy [7][8][9][10][11][12][13][14][15][16] . A necessary condition for SC within any interacting electrons model however is that interactions must enhance superconducting pair-pair correlations relative to the noninteracting model.…”

Section: Introductionmentioning

confidence: 99%

Coulomb enhancement of superconducting pair-pair correlations in a34-filled model forκ−(BEDT-TTF)2X

Silva¹,

Gomes²,

Mazumdar³

et al. 2016

Phys. Rev. B

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We present the results of precise correlated-electron calculations on the monomer lattices of the organic charge-transfer solids κ-(BEDT-TTF)2X for 32 and 64 molecular sites. Our calculations are for band parameters corresponding to X = Cu[N(CN)2]Cl and Cu2(CN)3, which are semiconducting antiferromagnetic and quantum spin liquid, respectively, at ambient pressure. We have performed our calculations for variable electron densities ρ per BEDT-TTF molecule, with ρ ranging from 1 to 2. We find that d-wave superconducting pair-pair correlations are enhanced by electron-electron interactions only for a narrow carrier concentration about ρ = 1.5, which is precisely the carrier concentration where superconductivity in the charge-transfer solids occurs. Our results indicate that the enhancement in pair-pair correlations is not related to antiferromagnetic order, but to a proximate hidden spin-singlet state that manifests itself as a charge-ordered state in other chargetransfer solids. Long-range superconducting order does not appear to be present in the purely electronic model, suggesting that electron-phonon interactions also must play a role in a complete theory of superconductivity.

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Phase Diagram of Superconductivity on the Anisotropic Triangular Lattice Hubbard Model: An Effective Model of κ-(BEDT-TTF) Salts

Cited by 189 publications

References 21 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

Paired electron crystal: Order from frustration in the quarter-filled band

Coulomb enhancement of superconducting pair-pair correlations in a34-filled model forκ−(BEDT-TTF)2X

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Phase Diagram of Superconductivity on the Anisotropic Triangular Lattice Hubbard Model: An Effective Model of κ-(BEDT-TTF) Salts

Cited by 189 publications

References 21 publications

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

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

Paired electron crystal: Order from frustration in the quarter-filled band

Coulomb enhancement of superconducting pair-pair correlations in a34-filled model forκ−(BEDT-TTF)2X

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

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