Pseudogap and singlet formation in organic and cuprate superconductors

Merino, Jaime; Gunnarsson, O.

doi:10.1103/physrevb.89.245130

Cited by 40 publications

(40 citation statements)

References 104 publications

(242 reference statements)

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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%

“…These Q ¼ 0 fluctuations are certainly strong in proximity of the superconducting phase, but they were also found [83] to be significant over short distances in the pseudogap regime. Their intensity gets stronger as U is increased, beyond the values where superconductivity exists.…”

Section: Fig 2 (Color Online) As Formentioning

confidence: 93%

“…For these parameters, the selfenergy (see upper panels of Fig. 2) displays strong momentum differentiation between the "antinodal" [K ¼ ð0; πÞ] and the "nodal" [K ¼ ðπ=2; π=2Þ] momentum, with a pseudogaplike behavior at the antinode [82,83].…”

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confidence: 99%

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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%

Section: Fig 2 (Color Online) As Formentioning

confidence: 93%

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

et al. 2015

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“…Comparing regimes where s-wave preformed pairs are certainly present or certainly absent, we identify which properties of the system are so sensitive to their presence to be exploited for their detection. Such an identification will also be applicable to interpret existing analyses of the pseudogap-phase in the cuprates 19,21,22 . We have structured our paper as follows: In Sec.…”

Section: Introductionmentioning

confidence: 98%

Detecting a preformed pair phase: Response to a pairing forcing field

2016

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The normal state of strongly coupled superconductors is characterized by the presence of "preformed" Cooper pairs well above the superconducting critical temperature. In this regime, the electrons are paired, but they lack the phase coherence necessary for superconductivity. The existence of preformed pairs implies the existence of a characteristic energy scale associated to a pseudogap. Preformed pairs are often invoked to interpret systems where some signatures of pairing are present without actual superconductivity, but an unambiguous theoretical characterization of a preformedpair system is still lacking. To fill this gap, we consider the response to an external pairing field of an attractive Hubbard model, which hosts one of the cleanest realizations of a preformed pair phase, and a repulsive model where s−wave superconductivity can not be realized. Using dynamical mean-field theory to study this response, we identify the characteristic features which distinguish the reaction of a preformed pair state from a normal metal without any precursor of pairing. The theoretical detection of preformed pairs is associated with the behavior of the second derivative of the order parameter with respect to the external field, as confirmed by analytic calculations in limiting cases. Our findings provide a solid testbed for the interpretation of state-of-the-art calculations for the normal state of the doped Hubbard model in terms of d−wave preformed pairs and, in perspective, of non-equilibrium experiments in high-temperature superconductors.

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“…A typical realization of the square-lattice Hubbard model is cuprate superconductors and related materials. Pseudogap state and superconductivity in those systems have been studied actively by using both the DCA [18][19][20] and CDMFT approaches [21][22][23][24][25][26][27][28] . Another typical realization of the two-dimensional Hubbard model is the organic materials κ-(BEDT-TTF) 2 X, and this has a triangular lattice structure.…”

Section: Dynamical Mean Field Theory (Dmft)mentioning

confidence: 99%

Publisher's Note: Cluster dynamical mean field theory study of antiferromagnetic transition in the square-lattice Hubbard model: Optical conductivity and electronic structure [Phys. Rev. B94, 085110 (2016)]

Sato¹,

Tsunetsugu²

2016

Phys. Rev. B

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We numerically study optical conductivity σ(ω) near the "antiferromagnetic" phase transition in the square-lattice Hubbard model at half filling. We use a cluster dynamical mean field theory and calculate conductivity including vertex corrections, and to this end, we have reformulated the vertex corrections in the antiferromagnetic phase. We find that the vertex corrections change various important details in temperature-and ω-dependencies of conductivity in the square lattice, and this contrasts sharply the case of the Mott transition in the frustrated triangular lattice. Generally, the vertex corrections enhance variations in the ω-dependence, and sharpen the Drude peak and a high-ω incoherent peak in the paramagnetic phase. They also enhance the dip in σ(ω) at ω=0 in the antiferromagnetic phase. Therefore, the dc conductivity is enhanced in the paramagnetic phase and suppressed in the antiferromagnetic phase, but this change occurs slightly below the transition temperature. We also find a temperature region above the transition temperature in which the dc conductivity shows an insulating behavior but σ(ω) retains the Drude peak, and this region is stabilized by the vertex corrections. We also investigate which fluctuations are important in the vertex corrections and analyze momentum dependence of the vertex function in detail.

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Pseudogap and singlet formation in organic and cuprate superconductors

Cited by 40 publications

References 104 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

Detecting a preformed pair phase: Response to a pairing forcing field

Publisher's Note: Cluster dynamical mean field theory study of antiferromagnetic transition in the square-lattice Hubbard model: Optical conductivity and electronic structure [Phys. Rev. B94, 085110 (2016)]

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