Novel Electronic State and Superconductivity in the Electron-Doped High-Tc T’-Superconductors

Adachi, Tadashi; Koike, Yasuhiro

doi:10.3390/condmat2030023

Cited by 29 publications

(23 citation statements)

References 74 publications

(138 reference statements)

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“…Several recent reviews have given excellent discussions of the experimental developments on the electron-doped cuprates [54][55][56] . There is general agreement that the difference between the electron-and hole-doped cuprates originates from their different crystal structures (T in the former versus predominantly T in the latter).…”

Section: A Experimental Puzzles: Electron-doped Materialsmentioning

confidence: 99%

Valence transition model of the pseudogap, charge order, and superconductivity in electron-doped and hole-doped copper oxides

Mazumdar

2018

Phys. Rev. B

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We present a valence transition model for electron-and hole-doped cuprates, within which there occurs a discrete jump in ionicity Cu 2+ → Cu 1+ in both families upon doping, at or near optimal doping in the conventionally prepared electron-doped compounds and at the pseudogap phase transition in the hole-doped materials. In thin films of the T compounds, the valence transition has occurred already in the undoped state. The phenomenology of the valence transition is closely related to that of the neutral-to-ionic transition in mixed-stack organic charge-transfer solids. Doped cuprates have negative charge-transfer gaps, just as rare earth nickelates and BaBiO3. The unusually high ionization energy of the closed shell Cu 1+ ion, taken together with the doping-driven reduction in three-dimensional Madelung energy and gain in two-dimensional delocalization energy in the negative charge transfer gap state drives the transition in the cuprates. The combined effects of strong correlations and small d − p electron hoppings ensure that the systems behave as effective 1 2 -filled Cu-band with the closed shell electronically inactive O 2− ions in the undoped state, and as correlated two-dimensional geometrically frustrated 1 4 -filled oxygen hole-band, now with electronically inactive closed-shell Cu 1+ ions, in the doped state. The model thus gives microscopic justification for the two-fluid models suggested by many authors. The theory gives the simplest yet most comprehensive understanding of experiments in the normal states. The robust commensurate antiferromagnetism in the conventional T crystals, the strong role of oxygen deficiency in driving superconductivity and charge carrier sign corresponding to holes at optimal doping are all manifestations of the same quantum state. In the hole-doped pseudogapped state, there occurs a biaxial commensurate period 4 charge density wave state consisting of O 1− -Cu 1+ -O 1− spin-singlets, that coexists with broken rotational C4 symmetry due to intraunit cell oxygen inequivalence. Finite domains of this broken symmetry state will exhibit two-dimensional chirality and the polar Kerr effect. Superconductivity within the model results from a destabilization of the 1 4 -filled band paired Wigner crystal [Phys. Rev. B 93, 165110 and 93, 205111]. We posit that a similar valence transition, Ir 4+ → Ir 3+ , occurs upon electron doping SrIr2O4. We make testable experimental predictions on cuprates including superoxygenated La2CuO 4+δ and iridates. Finally, as indirect evidence for the valence bond theory of superconductivity proposed here, we note that there exist an unusually large number of unconventional superconductors that exhibit superconductivity proximate to exotic charge ordered states, whose bandfillings are universally 1 4 or 3 4 , exactly where the paired Wigner crystal is most stable.

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Section: A Experimental Puzzles: Electron-doped Materialsmentioning

confidence: 99%

Valence transition model of the pseudogap, charge order, and superconductivity in electron-doped and hole-doped copper oxides

Mazumdar

2018

Phys. Rev. B

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“…[2] In the electron-doped cuprate, a short-range magnetic order due to a very small amount of excess oxygen is formed in the parent SC polycrystal of La 1.8 Eu 0.2 CuO 4+δ and the SC underdoped single crystal of Pr 1.3−x La 0.7 Ce x CuO 4 with x = 0.10. [15,16] The Cu-spin correlation is moderately developed in the overdoped PLCCO with x = 0.14 [20] and the development of the Cu-spin correlation almost disappears in the heavily overdoped PLCCO with x = 0.20 where the superconductivity disappears. Therefore, there is a similarity for both hole-doped and electron-doped cuprates in terms of the Cu-spin correlation, that is, the development of the Cu-spin correlation is observed in the SC region of the phase diagram.…”

Section: Methodsmentioning

confidence: 99%

“…[20] NMR experiments of the SC single crystal of Pr 1.3−x La 0.7 Ce x CuO 4 with x = 0.15 have also indicated the presence of AF spin fluctuations. [21] These suggest that, compared with the short-range magnetic order in the parent and underdoped samples, [15,16] the development of the Cu-spin correlation weakens with increasing x but is apparently observed in the slightly overdoped regime. In order to obtain detailed information on the low-energy Cu-spin correlation in the heavily overdoped regime and its relation to the superconductivity, we have carried out µSR measurements using PLCCO single crystals in the heavily overdoped regime of x = 0.17 and 0.20.…”

Section: Introductionmentioning

confidence: 99%

Muon-spin relaxation study of the spin correlations in the overdoped regime of electron-doped high- Tc cuprate superconductors

et al. 2019

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In order to investigate the low-energy antiferromagnetic Cu-spin correlation and its relation to the superconductivity, we have performed muon spin relaxation (µSR) measurements using single crystals of the electron-doped high-Tc cuprate Pr1−xLaCexCuO4 in the overdoped regime. The µSR spectra have revealed that the Cu-spin correlation is developed in the overdoped samples where the superconductivity appears. The development of the Cu-spin correlation weakens with increasing x and is negligibly small in the heavily overdoped sample where the superconductivity almost disappears. Considering that the Cu-spin correlation also exist in the superconducting electron-doped cuprates in the undoped and underdoped regimes [T. Adachi et al., J. Phys. Soc. Jpn. 85, 114716 (2016)], our findings suggest that the mechanism of the superconductivity is related to the low-energy Cu-spin correlation in the entire doping regime of the electron-doped cuprates.

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“…In subsequent studies of thin films and polycrystalline samples with the T ′ structure, superconductivity was observed even without Ce substitution (x = 0) when the oxygen concentration was carefully controlled [13][14][15]. These more recent findings triggered a reexamination of the effects of post-growth annealing [16,17]. A µSR study [18] revealed short-ranged magnetic correlations in superconducting polycrystalline La [20,21], where such signatures were associated with a significant increase of spin correlations on cooling.…”

Section: Introductionmentioning

confidence: 99%

Post-growth annealing effects on charge and spin excitations in Nd$_{2-x}$Ce$_x$CuO$_4$

Ishii,

Asano,

Ashida

et al. 2020

Preprint

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We report a Cu K-and L3-edge resonant inelastic x-ray scattering study of charge and spin excitations of bulk Nd2−xCexCuO4, with focus on post-growth annealing effects. For the parent compound Nd2CuO4 (x = 0), a clear charge-transfer gap is observed in the as-grown state, whereas the charge excitation spectra indicate that electrons are doped in the annealed state. This is consistent with the observation that annealed thin-film and polycrystalline samples of RE2CuO4 (RE = rare earth) can become metallic and superconducting at sufficiently high electron concentrations without Ce doping. For x = 0.16, a Ce concentration for which it is known that oxygen reduction destroys long-range antiferromagnetic order and induces superconductivity, we find that the highenergy spin excitations of non-superconducting as-grown and superconducting annealed crystals are nearly identical. This finding is in stark contrast to the significant changes in the low-energy spin excitations previously observed via neutron scattering.

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Novel Electronic State and Superconductivity in the Electron-Doped High-Tc T’-Superconductors

Cited by 29 publications

References 74 publications

Valence transition model of the pseudogap, charge order, and superconductivity in electron-doped and hole-doped copper oxides

Valence transition model of the pseudogap, charge order, and superconductivity in electron-doped and hole-doped copper oxides

Muon-spin relaxation study of the spin correlations in the overdoped regime of electron-doped high- Tc cuprate superconductors

Post-growth annealing effects on charge and spin excitations in Nd$_{2-x}$Ce$_x$CuO$_4$

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