Origin of the pseudogap in cuprate superconductors from quantum cluster theories

Merino, Jaime; Gunnarsson, O.

doi:10.1088/0953-8984/25/5/052201

Cited by 9 publications

(48 citation statements)

References 21 publications

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“…The latter cannot be interpreted, hence, in terms of preformed pairs. This scenario matches very well the different estimates of fluctuation strengths in previous DCA studies [83,86,87]. We also emphasize the general applicability of our result (see Supplemental Material [51]): A well-defined mode in one channel appears as short-lived fluctuations in other channels.…”

Section: Fig 2 (Color Online) As Forsupporting

confidence: 91%

Fluctuation Diagnostics of the Electron Self-Energy: Origin of the Pseudogap Physics

et al. 2015

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We demonstrate how to identify which physical processes dominate the low-energy spectral functions of correlated electron systems. We obtain an unambiguous classification through an analysis of the equation of motion for the electron self-energy in its charge, spin, and particle-particle representations. Our procedure is then employed to clarify the controversial physics responsible for the appearance of the pseudogap in correlated systems. We illustrate our method by examining the attractive and repulsive Hubbard model in two dimensions. In the latter, spin fluctuations are identified as the origin of the pseudogap, and we also explain why d-wave pairing fluctuations play a marginal role in suppressing the low-energy spectral weight, independent of their actual strength. Introduction.-Correlated electron systems display some of the most fascinating phenomena in condensed matter physics, but their understanding still represents a formidable challenge for theory and experiments. For photoemission [1] or STM [2,3] spectra, which measure single-particle quantities, information about correlation is encoded in the electronic self-energy Σ. However, due to the intrinsically many-body nature of the problems, even an exact knowledge of Σ is not sufficient for an unambiguous identification of the underlying physics. A perfect example of this is the pseudogap observed in the single-particle spectral functions of underdoped cuprates [4], and, more recently, of their nickelate analogues [5]. Although relying on different assumptions, many theoretical approaches provide self-energy results compatible with the experimental spectra. This explains the lack of a consensus about the physical origin of the pseudogap: In the case of cuprates, the pseudogap has been attributed to spin fluctuations [6-10], preformed pairs [11][12][13][14][15], Mottness [16,17], and, recently, to the interplay with charge fluctuations [18][19][20][21] or to Fermi-liquid scenarios [22]. The existence and the role of (d-wave) superconducting fluctuations [11][12][13][14][15] in the pseudogap regime are still openly debated for the basic model of correlated electrons, the Hubbard model.Experimentally, the clarification of many-body physics is augmented by a simultaneous investigation at the two-particle level, i.e., via neutron scattering [23], infrared or optical [24] and pump-probe spectroscopy [25], muon-spin relaxation [26], and correlation or coincidence two-particle spectroscopies [27][28][29]. Analogously, theoretical studies of Σ can also be supplemented by a corresponding analysis at the two-particle level. In this

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Section: Fig 2 (Color Online) As Forsupporting

confidence: 91%

Fluctuation Diagnostics of the Electron Self-Energy: Origin of the Pseudogap Physics

et al. 2015

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“…64 In fact, due to the relevance for the cuprate physics, the general problem of the pseudogap formation in the Hubbard model on a square lattice has been intensively investigated for embedded clusters, e.g., in DCA. 65,66 Based on studies for N c = 4 and 8, it has recently been argued that, for a sufficiently large U , a localized state |ψ loc is formed on the cluster, 64 leading to pseudogap features. More specifically, by comparing correlation functions of the DCA calculation and for |ψ loc , this state was identified 64 with a singlet, which -for N c = 4 we are considering here-takes the approximate form…”

Section: B Rvb State and Pseudogapmentioning

confidence: 99%

“…65,66 Based on studies for N c = 4 and 8, it has recently been argued that, for a sufficiently large U , a localized state |ψ loc is formed on the cluster, 64 leading to pseudogap features. More specifically, by comparing correlation functions of the DCA calculation and for |ψ loc , this state was identified 64 with a singlet, which -for N c = 4 we are considering here-takes the approximate form…”

Section: B Rvb State and Pseudogapmentioning

confidence: 99%

Parquet decomposition calculations of the electronic self-energy

et al. 2016

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The parquet decomposition of the self-energy into classes of diagrams, those associated with specific scattering processes, can be exploited for different scopes. In this work, the parquet decomposition is used to unravel the underlying physics of non-perturbative numerical calculations. We show the specific example of dynamical mean field theory (DMFT) and its cluster extensions (DCA) applied to the Hubbard model at half-filling and with hole doping: These techniques allow for a simultaneous determination of two-particle vertex functions and self-energies, and hence, for an essentially "exact" parquet decomposition at the single-site or at the cluster level. Our calculations show that the self-energies in the underdoped regime are dominated by spin scattering processes, consistent with the conclusions obtained by means of the fluctuation diagnostics approach [Phys. Rev. Lett. 114, 236402 (2015)]. However, differently from the latter approach, the parquet procedure displays important changes with increasing interaction: Even for relatively moderate couplings, well before the Mott transition, singularities appear in different terms, with the notable exception of the predominant spin-channel. We explain precisely how these singularities, which partly limit the utility of the parquet decomposition, and -more generally -of parquet-based algorithms, are never found in the fluctuation diagnostics procedure. Finally, by a more refined analysis, we link the occurrence of the parquet singularities in our calculations to a progressive suppression of charge fluctuations and the formation of an RVB state, which are typical hallmarks of a pseudogap state in DCA.

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“…The work presented here is an in-depth extension of our previous short paper [59] and is organized as follows. In Sec.…”

Section: Introductionmentioning

confidence: 99%

Pseudogap and singlet formation in organic and cuprate superconductors

Merino

Gunnarsson

2014

Phys. Rev. B

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The pseudogap phase occurring in cuprate and organic superconductors is analyzed based on the dynamical cluster approximation approach to the Hubbard model. In this method a cluster embedded in a self-consistent bath is studied. With increasing Coulomb repulsion, U , the antinodal point [k = (π,0)] displays a gradual suppression of spectral density of states around the Fermi energy which is not observed at the nodal point [k = (π/2,π/2)]. The opening of the antinodal pseudogap is found to be related to the internal structure of the cluster and the much weaker bath-cluster couplings at the antinodal than nodal point. The role played by internal cluster correlations is elucidated from a simple four-level model. For small U , the cluster levels form Kondo singlets with their baths leading to a peak in the spectral density. As U is increased a localized state is formed localizing the electrons in the cluster. If this cluster localized state is nondegenerate, the Kondo effect is destroyed and a pseudogap opens up in the spectra at the antinodal point. The pseudogap can be understood in terms of destructive interference between different paths for electrons hopping between the cluster and the bath. However, electrons at the nodal points remain in Kondo states up to larger U since they are more strongly coupled to the bath. The strong correlation between the (π,0) and the (0,π ) cluster levels in the localized state leads to a large correlation energy gain, which is important for localizing electrons and opening up a pseudogap at the antinodal point. Such a scenario is in contrast with two independent Mott transitions found in two-band systems with different bandwidths in which the localized cluster electron does not correlate strongly with any other cluster electron for intermediate U .The important intracluster sector correlations are associated with the resonating valence bond character of the cluster ground state containing d-wave singlet pairs. The low-energy excitations determining the pseudogap have suppressed d-wave pairing, indicating that the pseudogap can be related to breaking very short-range d-wave pairs. Geometrical frustration on the anisotropic triangular lattice relevant to κ-(BEDT-TTF) 2 X leads to a switch in the character of the ground state of the cluster at intermediate hopping ratios t /t ∼ 0.7. Electron doping of the frustrated square lattice destroys the pseudogap, in agreement with photoemission experiments on cuprates, due to a larger Schrieffer-Wolff exchange coupling, J K , and a stronger cluster-bath coupling for the antinodal point.

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Origin of the pseudogap in cuprate superconductors from quantum cluster theories

Cited by 9 publications

References 21 publications

Fluctuation Diagnostics of the Electron Self-Energy: Origin of the Pseudogap Physics

Fluctuation Diagnostics of the Electron Self-Energy: Origin of the Pseudogap Physics

Parquet decomposition calculations of the electronic self-energy

Pseudogap and singlet formation in organic and cuprate superconductors

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