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Li, Eric; Sharma, Rakesh; Ogale, Satishchandra; Zhao, Yinchang; Venkatesan, T.; Li, J. J.; Cao, Wenping; Lee, C. H.

doi:10.1103/physrevb.65.184519

Cited by 11 publications

(15 citation statements)

References 53 publications

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“…The EH-dimer, or coupled electron-hole pair, can be viewed as a "negative-U " center where U , or the recombination energy (the energy of the inverse disproportionation reaction) defines an energy scale of a robustness of the EHBL phase. 56,57 ). It seems to be likely that a famous 1.5 eV peak in the optical spectrum of superconducting 123 system that reveals a fairly sharp CPB resonance 57 can be assigned to a EH recombination transition with a minimal energy.…”

Section: Evolution Of Cuprates With Non-isovalent Substitutionmentioning

confidence: 99%

True charge-transfer gap in parent insulating cuprates

Moskvin¹

2011

Phys. Rev. B

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A large body of experimental data point towards a charge transfer instability of parent insulating cuprates to be their unique property. We argue that the true charge transfer gap in these compounds is as small as 0.4-0.5 eV rather than 1.5-2.0 eV as usually derived from the optical gap measurements. In fact we deal with a competition of the conventional (3d 9 ) ground state and a charge transfer (CT) state with formation of electron-hole dimers which evolves under doping to an unconventional bosonic system. Our conjecture does provide an unified standpoint on the main experimental findings for parent cuprates including linear and nonlinear optical, Raman, photoemission, photoabsorption, and transport properties anyhow related with the CT excitations. In addition we suggest a scenario for the evolution of the CuO2 planes in the CT unstable cuprates under a nonisovalent doping. II. ELECTRON-LATTICE RELAXATION AND CT INSTABILITY OF PARENT CUPRATESMinimal energy cost of the optically excited disproportionation or electron-hole formation due to a direct Franck-Condon (FC) CT transition in insulating cuprates is E opt gap ≈1.5-2 eV. This relatively small value of the optical gap is addressed to be an argument against the "negative-U " disproportionation reaction 2Cu(II) = Cu(III) + Cu(I) 9 , or more correctlyHowever, the question arises, what is the energy cost for the thermal excitation of such a local disproportionation?The answer implies first of all the knowledge of relaxation energy, or the energy gain due to the lattice polarization by the localized charges. The full polarization energy R includes the cumulative effect of electronic and ionic terms, related with the displacement of electron shells and ionic cores, respectively. The former term R opt is due

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Section: Evolution Of Cuprates With Non-isovalent Substitutionmentioning

confidence: 99%

True charge-transfer gap in parent insulating cuprates

Moskvin¹

2011

Phys. Rev. B

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“…The latter effect is not just atomic physics but the effect of the above new electron count upon the local cation/anion bonding interaction. The antibonding p/d hybridization that hitherto had held the chemical potential high at d 8 , and even at d 9 , now with d 10 becomes terminated. The d 10 closed shell is thereby freed to relax rapidly in energy to its new status, semi-corelike when uncharged, though here much distended, whilst the oxygen p states, no longer constituting stabilized partner within the dpσ bonding interaction, are freed to rise in energy up through the descending copper d-state set.…”

Section: Introduction To Boson-fermion Negative-u Crossover Modelling...mentioning

confidence: 99%

“…In the present case of the mixed-valent cuprates [5], the double-loading charge fluctuations in question are adequately represented by the intervalence, three-unit process 9 Note the double loading occurs here into coordination units that nominally carry trivalent Madelung charging by virtue of local counter-cation substitution and/or excess interstitial oxygen content. Moreover the double loading brings the local, shell-filling, configuration p 6 d 10 , and in its trivalent setting the d 10 shell then becomes greatly stabilized.…”

Section: Introduction To Boson-fermion Negative-u Crossover Modelling...mentioning

confidence: 99%

“…To arrive at this picture calls for a Hubbard negative-U value local to trivalent sites of −1.5 eV per electron [6], roughly the size of the d x2−y2 bandwidth. U takes its standard definition by reference to single loading-here the local trivalent condition 9 Cu…”

Section: Introduction To Boson-fermion Negative-u Crossover Modelling...mentioning

confidence: 99%

“…Within the mixed-valent environment of the HTSC cuprates the global level of E F is largely dictated not by 9 Cu 1− III but by the majority species 9 Cu 0 II . This means that the negative-U state 10 Cu 2− III will not find degeneracy with E F unless and until |U | per electron comes to possess roughly the bandwidth energy ∼ 1.5 eV (see figure 3 in [11]).…”

Section: Introduction To Boson-fermion Negative-u Crossover Modelling...mentioning

confidence: 99%

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On properly integrating the electronic Raman and optical infra-red spectra of high temperature superconducting cuprate materials

Wilson¹

2009

J. Phys.: Condens. Matter

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New electronic Raman and infra-red spectroscopy results from optimally and overdoped high temperature superconducting cuprate systems are interpreted in terms of the negative- U, boson-fermion crossover model. A distinction is made between those features which follow the condensate gap, 2Δ(p), and those that are set by the local pair binding energy, [Formula: see text]. The critical role of the doping level p(c) = 0.185 is highlighted in conjunction with the question of developing quasiparticle incoherence, making connection here with recent transport and related results. [Formula: see text] IR results for magnetic fields parallel and perpendicular to c prove particularly illuminating. The general scheme developed continues to embrace all experimental data very satisfactorily.

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Room temperature rectifying characteristics of epitaxial Y1Ba2Cu3−xZnxO7−δ (x=0.0,0.2) and Nb:SrTiO3 (Nb: 0.05%, 0.1%, 0.5%) heterojunctions

Ramadan

Ogale

Dhar

et al. 2006

Journal of Applied Physics

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We report on the fabrication and electrical characterization of epitaxial metal-semiconductor junctions between Y1Ba2Cu3O7−δ (YBCO) (optimally doped and Zn doped) and (001) Nb:SrTiO3 with different Nb concentrations (0.05%, 0.1%, and 0.5%). The current-voltage characteristics of such epitaxial junctions are nonlinear and rectifying, and these are dramatically enhanced with decreasing Nb concentration and Zn doping. Indeed, for the case of 0.05% Nb:STO, reverse breakdown voltage as high as −18V(−28V) is realized for optimally doped (Zn doped) YBCO. These data are analyzed within the framework of thermionic emission∕diffusion models for Schottky and metal-insulator-semiconductor-type junctions.

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Sharp resonant multiplet in femtosecond optical pair-breaking spectroscopy of optimally doped, underdoped, and Zn-dopedYBa2Cu3

Cited by 11 publications

References 53 publications

True charge-transfer gap in parent insulating cuprates

True charge-transfer gap in parent insulating cuprates

On properly integrating the electronic Raman and optical infra-red spectra of high temperature superconducting cuprate materials

Room temperature rectifying characteristics of epitaxial Y1Ba2Cu3−xZnxO7−δ (x=0.0,0.2) and Nb:SrTiO3 (Nb: 0.05%, 0.1%, 0.5%) heterojunctions

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