| 1. |
- Qvarford, M, et al.
(author)
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Photoemission and x-ray absorption study of superconducting and semiconducting Ba1-xKxBiO3 single crystals
- 1996
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 54:9, s. 6700-6707
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Journal article (peer-reviewed)abstract
- Semiconducting Ba0.9K0.1BiO3 and superconducting Ba0.6K0.4BiO3 single crystals cleaved in situ have been studied by core level and valence band photoelectron spectroscopy and O K edge x-ray absorption spectroscopy. It was found that the general shape of the valence band spectrum agrees with the shape predicted by band structure calculations, but the intensity near the Fermi level, was lower in the experimental spectrum as compared to the calculated. The O K edge spectra showed that the metallic phase is not related to the presence of doping inducted O 2p holes. This property of Ba1-xKxBiO3 shows that the semiconductor-metal transition of this system is of a different nature than that of the hole doped cuprate high-T-c superconductors. The core level photoemission spectra of the cations showed a small asymmetry for Ba0.9K0.1BiO3. Corresponding spectra for Ba0.6K0.4BiO3 showed a larger asymmetry resulting in a resolved high binding energy shoulder in the Bi 4f spectrum. The origin of this feature is discussed.
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| 4. |
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| 5. |
- Qvarford, M, et al.
(author)
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Doping dependence of the O 1s is core-level photoemission in bi-Sr-Ca-Cu-O superconductors
- 1996
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 53:22, s. 14753-14756
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Journal article (peer-reviewed)abstract
- The O 1s core level of three different Bi-Sr-Ca-Cu-O superconductors has been studied by means of high-resolution x-ray-photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS). The O 1a XPS spectra could be decomposed into three components that were unambiguously assigned to the emission from the three different oxide layers in the crystal structure. These are, in order of increasing binding energy, Cu-O-2, Sr-O, and Bi-O. Furthermore, the component assigned to the Cu-O-2 layers exhibits a shift which depends on the hole doping as monitored by the XAS spectra.
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| 6. |
- Qvarford, M, et al.
(author)
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Doping dependence of the O 1s is core-level photoemission in bi-Sr-Ca-Cu-O superconductors
- 1996
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In: PHYSICAL REVIEW B-CONDENSED MATTER. - : AMER INST PHYSICS. - 0163-1829. ; 53:22, s. 14753-14756
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Journal article (other academic/artistic)abstract
- The O 1s core level of three different Bi-Sr-Ca-Cu-O superconductors has been studied by means of high-resolution x-ray-photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS). The O 1a XPS spectra could be decomposed into three component
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| 8. |
- Soderholm, S, et al.
(author)
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A photoelectron spectroscopy and x-ray absorption study of Bi2Sr2CaCu2O8 single crystal with adsorbed Cs : On the origin of the states affected by electron doping and evidence for spatially resolved electron doping
- 1996
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 8:9, s. 1307-1320
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Journal article (peer-reviewed)abstract
- The influence of electron doping, via deposition of small amounts of Cs, on the electronic structure of Bi2Sr2CaCu2O8 has been studied by high-resolution photoelectron spectroscopy (PES) and x-ray absorption spectroscopy (XAS), utilizing synchrotron radiation. The changes in the electronic structure were monitored by PES of the valence band and of the O Is, Bi 4f, Bi 5d, Ca 2p and Sr 3d core levels, and by XAS at the O Is, Cu 2p and Ca 2p edges. The experimental data suggest that the loss of the Fermi edge and the loss of spectral intensity down to about 2 eV below the Fermi level, and the substantial loss of spectral intensity of the pre-edge structure in the O 1s XAS spectrum are mainly due to annihilation of states with O 2p character in the Cu-O layer. It is evident from bulk- and surface-sensitive XAS spectra that the electron doping by Cs affects the electronic structure more strongly close to the surface. This implies that the doping occurs locally and that the charge transfer between the different layers in the unit cell is not uniform. Thus it seems possible to alter the electronic properties of Bi2Sr2CaCu2O8 locally through spatially resolved electron doping. When larger amounts of Cs are deposited, a chemical reaction occurs which causes a disruption of the Bi-O layer. This deposition regime is characterized by the presence of caesium oxide and reduced (metallic) Bi.
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| 9. |
- TJERNBERG, O, et al.
(author)
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ANGLE-RESOLVED PHOTOEMISSION ON NIO - ON THE NATURE OF THE VALENCE-BAND
- 1995
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In: Vacuum. - 0042-207X .- 1879-2715. ; 46:8-10, s. 1215-1218
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Journal article (peer-reviewed)abstract
- Angle resolved photoelectron spectroscopy has been performed on the valence band of NiO at the National Swedish Laboratory for Synchrotron Radiation. Normal emission spectra have been recorded for photon energies between 17 and 140 eV in order to study the electronic structure of the valence band. The experimentally determined band structure has been compared with a local density augmented plane wave band structure calculation. Signs of the influence of antiferromagnetic ordering are found and the general agreement between experimental and theoretical oxygen derived bands indicates strong hybridization between Ni 3d and O 2p orbitals.
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| 10. |
- Tjernberg, O, et al.
(author)
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Evidence of pseudogap related core level shifts in Bi2Sr2Ca1-xYxCu2O8+delta
- 1997
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 79:3, s. 499-502
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Journal article (peer-reviewed)abstract
- Photoelectron spectroscopy data from Bi2Sr2Ca1-xYxCu2O8+delta Single crystals, for x = 0, 0.16, and 0.55, are presented. It is shown that there are core level shifts related to the opening of a pseudogap and that similar shifts are observed at the opening of the superconducting gap in optimally doped samples. This result is in agreement with pair formation above T-c as suggested by V.J. Emery and S.A. Kivelson [Nature (London) 374, 434 (1995)].
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