Abstract
Electron-enery loss spectroscopy measurements on n-type doped high temperature superconductors, their undoped parent compounds, Y-doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and some rare earth oxides are presented. The undoped parent compounds Ln{sub 2}CuO{sub 4} (Ln = Pr, Nd, Sm) are charge transfer insulators with a charge transfer energy gap of 1.4 eV. The conduction band lies in the CuO{sub 2} plane and has mainly Cu3d{sub x}{sup 2}-y{sup 2} character. O2p{sub x,y} states are slightly hybridized with this band. Upon partially substituting the trivalent Ln ions by tetravalent Ce or Th and monovalent F for the O ions, electron doping of the CuO{sub 2} plane occurs with the electrons having mainly Cu3d character. A rigid band behaviour is proposed by several band structure calculations could be ruled out, as well as the occurence of so called `mid-gap` states appearing inside the band gap between the valence and conduction bands. The position of the Fermi level was found to be at the bottom of the conduction bands. No measurable influence of the reduction process, necessary to obtain superconductivity, was detected in the unoccupied density of states. Characteristics shifts of the measured oxygen and copper edges were correlated with crossing the metal-insulator transition.
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Citation Formats
Alexander, M.
Electron energy-loss spectroscopy on n-type doped high-temperature superconductors and related systems; Elektronenenergieverlustspektroskopie an n-dotierten Hochtemperatursupraleitern und verwandten Systemen.
Germany: N. p.,
1992.
Web.
Alexander, M.
Electron energy-loss spectroscopy on n-type doped high-temperature superconductors and related systems; Elektronenenergieverlustspektroskopie an n-dotierten Hochtemperatursupraleitern und verwandten Systemen.
Germany.
Alexander, M.
1992.
"Electron energy-loss spectroscopy on n-type doped high-temperature superconductors and related systems; Elektronenenergieverlustspektroskopie an n-dotierten Hochtemperatursupraleitern und verwandten Systemen."
Germany.
@misc{etde_10148235,
title = {Electron energy-loss spectroscopy on n-type doped high-temperature superconductors and related systems; Elektronenenergieverlustspektroskopie an n-dotierten Hochtemperatursupraleitern und verwandten Systemen}
author = {Alexander, M}
abstractNote = {Electron-enery loss spectroscopy measurements on n-type doped high temperature superconductors, their undoped parent compounds, Y-doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and some rare earth oxides are presented. The undoped parent compounds Ln{sub 2}CuO{sub 4} (Ln = Pr, Nd, Sm) are charge transfer insulators with a charge transfer energy gap of 1.4 eV. The conduction band lies in the CuO{sub 2} plane and has mainly Cu3d{sub x}{sup 2}-y{sup 2} character. O2p{sub x,y} states are slightly hybridized with this band. Upon partially substituting the trivalent Ln ions by tetravalent Ce or Th and monovalent F for the O ions, electron doping of the CuO{sub 2} plane occurs with the electrons having mainly Cu3d character. A rigid band behaviour is proposed by several band structure calculations could be ruled out, as well as the occurence of so called `mid-gap` states appearing inside the band gap between the valence and conduction bands. The position of the Fermi level was found to be at the bottom of the conduction bands. No measurable influence of the reduction process, necessary to obtain superconductivity, was detected in the unoccupied density of states. Characteristics shifts of the measured oxygen and copper edges were correlated with crossing the metal-insulator transition. These shifts are most probably caused by an improved screening capacity of the free charge carriers. A similar effect was also observed in Y-doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. Thus, it was possible to show that the disappearance of the valence band hole states upon doping did not occur in a rigid-band-like manner. The low energy excitations in Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4-{delta}} showed a plasmon like excitation at about 1 eV as well as a reduction and an energy shift of the charge transfer excitation. The dispersion of this plasmon excitation was determined. (orig.).}
place = {Germany}
year = {1992}
month = {Aug}
}
title = {Electron energy-loss spectroscopy on n-type doped high-temperature superconductors and related systems; Elektronenenergieverlustspektroskopie an n-dotierten Hochtemperatursupraleitern und verwandten Systemen}
author = {Alexander, M}
abstractNote = {Electron-enery loss spectroscopy measurements on n-type doped high temperature superconductors, their undoped parent compounds, Y-doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and some rare earth oxides are presented. The undoped parent compounds Ln{sub 2}CuO{sub 4} (Ln = Pr, Nd, Sm) are charge transfer insulators with a charge transfer energy gap of 1.4 eV. The conduction band lies in the CuO{sub 2} plane and has mainly Cu3d{sub x}{sup 2}-y{sup 2} character. O2p{sub x,y} states are slightly hybridized with this band. Upon partially substituting the trivalent Ln ions by tetravalent Ce or Th and monovalent F for the O ions, electron doping of the CuO{sub 2} plane occurs with the electrons having mainly Cu3d character. A rigid band behaviour is proposed by several band structure calculations could be ruled out, as well as the occurence of so called `mid-gap` states appearing inside the band gap between the valence and conduction bands. The position of the Fermi level was found to be at the bottom of the conduction bands. No measurable influence of the reduction process, necessary to obtain superconductivity, was detected in the unoccupied density of states. Characteristics shifts of the measured oxygen and copper edges were correlated with crossing the metal-insulator transition. These shifts are most probably caused by an improved screening capacity of the free charge carriers. A similar effect was also observed in Y-doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. Thus, it was possible to show that the disappearance of the valence band hole states upon doping did not occur in a rigid-band-like manner. The low energy excitations in Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4-{delta}} showed a plasmon like excitation at about 1 eV as well as a reduction and an energy shift of the charge transfer excitation. The dispersion of this plasmon excitation was determined. (orig.).}
place = {Germany}
year = {1992}
month = {Aug}
}