Temperature Dependence of the Optical Spectral Weight in the Cuprates: Role of Electron Correlations

Toschi, A.; Capone, Massimo; Ortolani, Michele; Calvani, P.; Lupi, S.; Castellani, C.

doi:10.1103/physrevlett.95.097002

Cited by 69 publications

(98 citation statements)

References 29 publications

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“…For the U > U c2 calculation, we have used the scale W * = 2.25 eV to convert the theoretical results to physical units. We see that for U > U c2 the calculated spectral weight is qualitatively inconsistent with the data 16 , because it vanishes as doping tends to zero. However, we note that in the qualitative comparison, the decisive feature is the behaviour at x < 0.1 where the uncertainties in the data are largest.…”

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confidence: 39%

Optical conductivity and the correlation strength of high-temperature copper-oxide superconductors

et al. 2008

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Since their discovery in 1986, the high-temperature copper-oxide superconductors have been a central object of study in condensed-matter physics. Their highly unusual properties are widely (although not universally) believed to be a consequence of electron-electron interactions that are so strong that the traditional paradigms of condensed-matter physics do not apply: instead, entirely new concepts and techniques are required to describe the physics. In particular, the superconductivity is obtained by adding carriers to insulating 'parent compounds'. These parent compounds have been identified 1 as 'Mott' insulators, in which the lack of conduction arises from anomalously strong electron-electron repulsion. The unusual properties of Mott insulators are widely 2 believed to be responsible for the high-temperature superconductivity. Here, we present a comparison of new theoretical calculations and published 3-8 optical conductivity measurements, which challenges this belief. The analysis indicates that the correlation strength in the cuprates is not as strong as previously believed, in particular that the materials are not properly regarded as Mott insulators. Rather, antiferromagnetism seems to be necessary to obtain the insulating state. By implication, antiferromagnetism is essential to the properties of the doped metallic and superconducting state as well.The prototypical 'parent compound' is La 2 CuO 4 , in which the lattice structure and electron counting is such that there is an odd number of electrons per formula unit. Thus, in the absence of further symmetry breaking, conventional band theory would predict that the material is a good metal. La 2 CuO 4 is however not metallic; it is an insulator with a gap determined by optical spectroscopy to be approximately 1.8 eV (refs 3,4). From one perspective, the insulating behaviour is not surprising. At temperature T = 0, La 2 CuO 4 has two-sublattice Néel order, so that the magnetic unit cell contains two formula units and thus an even number of electrons, compatible with the observed insulating behaviour. However, the consensus has been that the antiferromagnetic order is irrelevant. Instead, the materials have been identified 1,2 as 'Mott insulators' . (Although the cuprates are properly regarded as 'charge-transfer' and not 'Mott' insulators in the sense of ref. 9, we believe this issue is not relevant here: the high-energy-scale physics and chemistry of transition metal (Cu) and ligand (O) ions produces one band of electrons, with an effective interaction strength U which we aim to determine. In particular, optical data show that the nearest bands (arising mainly from the non-bonding oxygen orbitals) are 5-6 eV removed in energy, with only a weak absorption tail extending down to the energies of relevance here. The issue is discussed in more detail in the Supplementary Information.) In a Mott or charge-transfer insulator, the electron-electron interactions are so strong that a density of one electron per unit cell implies a 'jammed' situation: no electron ca...

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confidence: 39%

Optical conductivity and the correlation strength of high-temperature copper-oxide superconductors

et al. 2008

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“…A similar variation as large as 4 − 5% of the total SW integrated below 2.0 eV has been observed in the normal state of high-T c cuprates and quantitatively described by DMFT calculations, with the introduction of strong correlation effects [15,16]. By this approach, the temperature dependence of the SW is controlled by renormalized quasiparticle dispersion near the Fermi level.…”

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confidence: 69%

“…Recent theoretical and experimental advances have demonstrated that electronic correlations profoundly influence the optical response at energies up to several eV. [6,15,16,17,18,19]. Spectroscopic ellipsometry allows one to accurately detect such modifications and is hence a highly distinctive probe of electronic correlations in transition metal oxides [18,19].…”

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confidence: 99%

“…Spectroscopic ellipsometry allows one to accurately detect such modifications and is hence a highly distinctive probe of electronic correlations in transition metal oxides [18,19]. Dynamical mean-field theory (DMFT) calculations explain many aspects of strong temperature and doping dependent modifications of the optical spectral weight (SW) in the normal state of the superconducting cuprates [15,16,17]. Very recent DMFT studies indicate that LaFeAsO is slightly below the critical value of the Hubbard U required to obtain an insulating state [6,7].…”

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confidence: 99%

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Signatures of Electronic Correlations in Optical Properties ofLaFeAsO1−xFx

et al. 2009

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“…For overdoped compounds, this change is a decrease, 13,14 but for underdoped and optimal doped compounds, two groups [9][10][11][12] found an increase, though other groups found either no additional effect 15,16 or a decrease. 17 The finite cutoff was taken into account in several theoretical analyses of the T dependence of the optical integralfor instance, work based on the Hubbard model, 18 the t-J model, 14 and the d-density-wave model. 19 In Ref.…”

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confidence: 99%

Optical integral in the cuprates and the question of sum-rule violation

Norman

Chubukov²,

Heumen

et al. 2007

Phys. Rev. B

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Much attention has been given to a possible violation of the optical sum rule in the cuprates and the connection this might have to kinetic energy lowering. The optical integral is composed of a cutoffindependent term ͑whose temperature dependence is a measure of the sum-rule violation͒, plus a cutoffdependent term that accounts for the extension of the Drude peak beyond the upper bound of the integral. We find that the temperature dependence of the optical integral in the normal state of the cuprates can be accounted for solely by the latter term, implying that the dominant contribution to the observed sum-rule violation in the normal state is due to the finite cutoff. This cutoff-dependent term is well modeled by a theory of electrons interacting with a broad spectrum of bosons.

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Temperature Dependence of the Optical Spectral Weight in the Cuprates: Role of Electron Correlations

Cited by 69 publications

References 29 publications

Optical conductivity and the correlation strength of high-temperature copper-oxide superconductors

Optical conductivity and the correlation strength of high-temperature copper-oxide superconductors

Signatures of Electronic Correlations in Optical Properties ofLaFeAsO1−xFx

Optical integral in the cuprates and the question of sum-rule violation

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