Functional renormalization group study of orbital fluctuation mediated superconductivity: Impact of the electron-boson coupling vertex corrections

Tazai, Rina; Yamakawa, Youichi; Tsuchiizu, Masahisa; Kontani, Hiroshi

doi:10.1103/physrevb.94.115155

Cited by 28 publications

(29 citation statements)

References 27 publications

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“…However, recent dynamic mean field theory calculations have shown that robust s-wave superconductivity driven by local spin fluctuations is found in solutions to the Kondo lattice model, which is commonly used to describe heavy-fermion metals ( 49 ). Other recent theoretical work has shown that electron-phonon coupling could be strongly enhanced near a QCP again, stabilizing s-wave superconductivity ( 50 ). Our results might therefore support a new type of unconventional superconductivity where the gap function is s-wave but the pairing is nevertheless driven by strong magnetic fluctuations.…”

Section: Discussionmentioning

confidence: 99%

Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu ₂ Si ₂

et al. 2017

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Section: Discussionmentioning

confidence: 99%

Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu ₂ Si ₂

et al. 2017

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“…S3(a) in the SM:D [16], the full-gap s ++ state without any sign reversal corresponds to the largest eigenvalue for a wide region with α C ≥ 0.8. The obtained λ for the full-gap s ++ state is very large, since the attractive (repulsive) interaction is enlarged (suppressed) by |Λ c(s) | 2 [18][19][20]. Thus, T c for the full-gap s-wave state is expected to be high.…”

Section: (D) and λmentioning

confidence: 99%

Plain s-Wave Superconductivity near Magnetic Criticality: Enhancement of Attractive Electron–Boson Coupling Vertex Corrections

et al. 2017

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Recent experiments revealed that the plain s-wave state without any sign-reversal emerges in various metals near magnetic criticality. To understand this counter-intuitive phenomenon, we study the gap equation for the multiorbital Hubbard-Holstein model, by analyzing the vertex correction (VC) due to the higher-order electron-correlation effects. We find that the phonon-mediated orbital fluctuations are magnified by the VC for the susceptibility (χ-VC). In addition, the charge-channel attractive interaction is enlarged by the VC for the coupling-constant (U -VC), which is significant when the interaction has prominent q-dependences; therefore the Migdal theorem fails. Due to both χ-VC and U -VC, the plain s-wave state is caused by the small electron-phonon interaction near the magnetic criticality against the repulsive Coulomb interaction. We find that the direct Coulomb repulsion for the plain s-wave Cooper pair is strongly reduced by the "multiorbital screening effect." Keywords: orbital fluctuations, self-consistent vertex correction theory, magnetic quantum criticality It is widely believed that the spin-fluctuations are harmful for the conventional s-wave superconductivity. However, recent experiments have revealed that the plain s-wave state without any sign-reversal emerges in some strongly-correlated metals near the magnetic instability. For example, plain s-wave superconductivity with high T c is reported in heavily electron-doped FeSe families (T c = 60 ∼ 100K) [1, 2] and in A 3 C 60 (A =K, Rb, Cs; T c > 30K) [3]. In both compounds, electron-phonon (e-ph) interaction may play a crucial role in the pairing mechanism, as discussed in Refs. [4][5][6][7][8][9][10]. Even so, a fundamental question is why the high-T c plain s-wave state appears against the repulsive interaction by spinfluctuations. More surprisingly, the plain s-wave state is reported in heavy-fermion superconductor CeCu 2 Si 2 near the magnetic phase, according to the measurements of the specific heat, penetration depth, thermal conductivity, and electron irradiation effect on T c [11,12].Therefore, it is a significant problem for theorists to establish a general mechanism of the plain s-wave superconductivity in strongly correlated electron systems. One important feature of these s-wave superconductors would be the orbital degrees of freedom. In this case, in principle, the pairing glue for the plain s-wave state may be realized by the orbital fluctuations. The two possible origins of the orbital fluctuations are the higherorder many-body process given by the vertex correction (VC) [13] and the e-ph interaction [14]. The significant questions are (i) whether these two different origins of the orbital fluctuations (i.e., the VC due to Coulomb interaction and the e-ph interaction) cooperate or not, (ii) why the high-T c plain s-wave state is realized against the strong magnetic fluctuations, and (iii) how the plain swave Cooper pairs escape from the strong direct Coulomb repulsion in multiorbital systems.In this paper, we analyze a canonica...

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“…In an effort to establish more reliable RG to apply twodimensional electrons, the RG+cRPA method has been recently developed 56,[75][76][77][78][79][80] . We show the diagrammatic explanation of the RG+cRPA method in Fig.…”

Section: B Rg+crpa With Form Factormentioning

confidence: 99%

“…From now on, we analyze the dimer Hubbard model by applying the RG+cRPA method 96 . The RG+cRPA method is an efficient hybrid method between the RG and the RPA 46,56,78,80 . Here, we introduce the higher-energy cutoff Λ 0 (= 2).…”

Section: D/p-wave Bond/slc Order In Cupratesmentioning

confidence: 99%

$d$- and $p$-wave quantum liquid crystal orders in cuprate superconductors, $κ$-(BEDT-TTF)$_2$X, and coupled chain Hubbard models: functional-renormalization-group analysis

Tazai,

Yamakawa,

Tsuchiizu

et al. 2021

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Unconventional symmetry breaking without spin order, such as the rotational symmetry breaking (=nematic or smectic) orders as well as the spontaneous loop-current orders, have been recently reported in cuprate superconductors and their related materials. They are theoretically represented by non-A1g symmetry breaking in self-energy, which we call the form factor f k,q . In this paper, we analyze typical Hubbard models by applying the renormalization-group (RG) method, and find that various unconventional ordering emerges due to the quantum interference among spin fluctuations. Due to this mechanism, nematic (q = 0) and smectic (q = 0) bond orders with d-wave form factor f k,q ∝ cos kx − cos ky appear in both cuprates and κ-(BEDT-TTF)2X. The derived bond orders naturally explain the pseudogap behaviors in these compounds. The quantum interference also induces various current orders with odd-parity form factor. For example, we find the emergence of the charge and spin loop-current orders with p-wave form factor in geometrically frustrated Hubbard models. Thus, rich quantum phase transitions with d-and p-wave form factors are driven by the paramagnon interference in many low-dimensional Hubbard models.

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Functional renormalization group study of orbital fluctuation mediated superconductivity: Impact of the electron-boson coupling vertex corrections

Cited by 28 publications

References 27 publications

Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu ₂ Si ₂

Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu ₂ Si ₂

Plain s-Wave Superconductivity near Magnetic Criticality: Enhancement of Attractive Electron–Boson Coupling Vertex Corrections

$d$- and $p$-wave quantum liquid crystal orders in cuprate superconductors, $κ$-(BEDT-TTF)$_2$X, and coupled chain Hubbard models: functional-renormalization-group analysis

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Functional renormalization group study of orbital fluctuation mediated superconductivity: Impact of the electron-boson coupling vertex corrections

Cited by 28 publications

References 27 publications

Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu 2 Si 2

Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu 2 Si 2

Plain s-Wave Superconductivity near Magnetic Criticality: Enhancement of Attractive Electron–Boson Coupling Vertex Corrections

$d$- and $p$-wave quantum liquid crystal orders in cuprate superconductors, $κ$-(BEDT-TTF)$_2$X, and coupled chain Hubbard models: functional-renormalization-group analysis

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Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu ₂ Si ₂

Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu ₂ Si ₂