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Electron Spectroscopy Studies of Cuprate and Bismuthate Superconductors

Qvarford, Mats (1996)
Abstract
The electronic structure of the cuprate superconductors Bi(2)Sr(2)CaCu(2)O(8) and Bi(2)Sr(2)CuO(6) and the bismuthate superconductor Ba(0.6)K(0.4)BiO(3), as well as semiconducting Ba(0.9)K(0.1)BiO(3), have been studied by electron spectroscopy techniques. The intention has been to investigate fundamental properties of the metallic state such as the importance of strong electron correlations. In addition, the chemical and electronic influences from metal-overlayers, Cs, Cu, Ag and Au, on Bi(2)Sr(2)CaCu(2)O(8) have been studied. The spectroscopy techniques comprised photoemission, X-ray absorption and resonant photoemission. All samples studied were single crystals cleaved in situ. Polarisation dependent X-ray absorption at the Cu L3 and O K... (More)
The electronic structure of the cuprate superconductors Bi(2)Sr(2)CaCu(2)O(8) and Bi(2)Sr(2)CuO(6) and the bismuthate superconductor Ba(0.6)K(0.4)BiO(3), as well as semiconducting Ba(0.9)K(0.1)BiO(3), have been studied by electron spectroscopy techniques. The intention has been to investigate fundamental properties of the metallic state such as the importance of strong electron correlations. In addition, the chemical and electronic influences from metal-overlayers, Cs, Cu, Ag and Au, on Bi(2)Sr(2)CaCu(2)O(8) have been studied. The spectroscopy techniques comprised photoemission, X-ray absorption and resonant photoemission. All samples studied were single crystals cleaved in situ. Polarisation dependent X-ray absorption at the Cu L3 and O K edges and X-ray absorption at the Ca L2,3 edge demonstrated the anisotropy of the cuprate superconductors.



The lowest unoccupied Cu 3d and O 2p orbitals were measured to be mainly oriented parallel to the Cu-O(2) layers. Ca in Bi(2)Sr(2)CaCu(2)O(8), situated in between adjacent Cu-O(2) layers, behaved as being ionic, supporting the view that the Ca-layer in Bi(2)Sr(2)CaCu(2)O(8) can be regarded as a passive buffer layer between conducting Cu-O(2) layers. Resonant photoemission at the Cu L3 edge together with Cu 2p3/2 core level photoemission were used to study the effects from strong correlation among the Cu 3d electrons in Bi(2)Sr(2)CaCu(2)O(8) and Bi(2)Sr(2)CuO(6). The satellite emissions made it possible to obtain, within a simplified cluster-configuration-interaction model, quantitative information about model-Hamiltonian parameters describing the electron correlation. Based on this analysis, the materials were classified as doped charge-transfer insulators. High energy resolution O 1s core level photoemission of three different Bi-Sr-Ca-Cu-O superconductors revealed a doping dependent binding energy shift for the component assigned to the Cu-O(2) layers.



This result demonstrated that high resolution O 1s photoemission can be used to study the hole doping of cuprate high-Tc superconductors. Cu overlayers on Bi(2)Sr(2)CaCu(2)O(8) gave rise to a strong chemical reaction, a breaking of Bi-O bonds, at the substrate surface. A similar, but very weak, reaction were found for Ag, Au and Cs at rather high coverage. At lower coverage Cs affected the hole doping of the substrate without any detectable chemical reaction. Valence band spectra for Ba(1-x)K(x)BiO(3) (x equals 0.1 or 0.4) were found to agree well with the prediction from band structure calculations, whereas O K edge X-ray absorption showed that the metallic phase of Ba(1-x)K(x)BiO(3) is not related to the presence of doping induced O 2p holes. Both these results point out fundamental differences between Ba(1-x)K(x)BiO(3) and cuprate high-Tc superconductors. (Less)
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author
opponent
  • Prof Braicovich, L.
publishing date
type
Thesis
publication status
published
subject
keywords
metal overlayer, electronic structure, resonant photoemission, X-ray absorption, photoemission, high-Tc superconductor, electron correlation, Physics, Fysik, Fysicumarkivet A:1996:Qvarford
pages
50 pages
publisher
Synchrotron Radiation Research
defense location
Lecture Hall B, Institute of Physics
defense date
1996-02-16 10:15
external identifiers
  • Other:ISRN: LUNFD6/NFSF--96/1007--SE
ISBN
91-628-1880-5
language
English
LU publication?
no
id
f3b6d810-32b3-4373-8b87-7cbb7e8e3912 (old id 28172)
date added to LUP
2007-06-08 14:46:38
date last changed
2016-09-19 08:45:11
@misc{f3b6d810-32b3-4373-8b87-7cbb7e8e3912,
  abstract     = {The electronic structure of the cuprate superconductors Bi(2)Sr(2)CaCu(2)O(8) and Bi(2)Sr(2)CuO(6) and the bismuthate superconductor Ba(0.6)K(0.4)BiO(3), as well as semiconducting Ba(0.9)K(0.1)BiO(3), have been studied by electron spectroscopy techniques. The intention has been to investigate fundamental properties of the metallic state such as the importance of strong electron correlations. In addition, the chemical and electronic influences from metal-overlayers, Cs, Cu, Ag and Au, on Bi(2)Sr(2)CaCu(2)O(8) have been studied. The spectroscopy techniques comprised photoemission, X-ray absorption and resonant photoemission. All samples studied were single crystals cleaved in situ. Polarisation dependent X-ray absorption at the Cu L3 and O K edges and X-ray absorption at the Ca L2,3 edge demonstrated the anisotropy of the cuprate superconductors.<br/><br>
<br/><br>
The lowest unoccupied Cu 3d and O 2p orbitals were measured to be mainly oriented parallel to the Cu-O(2) layers. Ca in Bi(2)Sr(2)CaCu(2)O(8), situated in between adjacent Cu-O(2) layers, behaved as being ionic, supporting the view that the Ca-layer in Bi(2)Sr(2)CaCu(2)O(8) can be regarded as a passive buffer layer between conducting Cu-O(2) layers. Resonant photoemission at the Cu L3 edge together with Cu 2p3/2 core level photoemission were used to study the effects from strong correlation among the Cu 3d electrons in Bi(2)Sr(2)CaCu(2)O(8) and Bi(2)Sr(2)CuO(6). The satellite emissions made it possible to obtain, within a simplified cluster-configuration-interaction model, quantitative information about model-Hamiltonian parameters describing the electron correlation. Based on this analysis, the materials were classified as doped charge-transfer insulators. High energy resolution O 1s core level photoemission of three different Bi-Sr-Ca-Cu-O superconductors revealed a doping dependent binding energy shift for the component assigned to the Cu-O(2) layers.<br/><br>
<br/><br>
This result demonstrated that high resolution O 1s photoemission can be used to study the hole doping of cuprate high-Tc superconductors. Cu overlayers on Bi(2)Sr(2)CaCu(2)O(8) gave rise to a strong chemical reaction, a breaking of Bi-O bonds, at the substrate surface. A similar, but very weak, reaction were found for Ag, Au and Cs at rather high coverage. At lower coverage Cs affected the hole doping of the substrate without any detectable chemical reaction. Valence band spectra for Ba(1-x)K(x)BiO(3) (x equals 0.1 or 0.4) were found to agree well with the prediction from band structure calculations, whereas O K edge X-ray absorption showed that the metallic phase of Ba(1-x)K(x)BiO(3) is not related to the presence of doping induced O 2p holes. Both these results point out fundamental differences between Ba(1-x)K(x)BiO(3) and cuprate high-Tc superconductors.},
  author       = {Qvarford, Mats},
  isbn         = {91-628-1880-5},
  keyword      = {metal overlayer,electronic structure,resonant photoemission,X-ray absorption,photoemission,high-Tc superconductor,electron correlation,Physics,Fysik,Fysicumarkivet A:1996:Qvarford},
  language     = {eng},
  pages        = {50},
  publisher    = {ARRAY(0x85d36e0)},
  title        = {Electron Spectroscopy Studies of Cuprate and Bismuthate Superconductors},
  year         = {1996},
}