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Photoelectron Spectroscopy of High Temperature Superconductors and Related Compounds

Nylén, Henrik LU (1998)
Abstract
In this thesis, the high temperature superconductors (HTSC) Ba<sub>0.6</sub>K<sub>0.4</sub>BiO<sub>3</sub>, La<sub>2</sub>CuO<sub>4+x</sub>, Bi<sub>2</sub>Sr<sub>2</sub>Ca<sub>1-x</sub>Y<sub>x</sub>Cu<sub>2</sub>O<sub> 8+d</sub>, Bi<sub>2</sub>Sr<sub>2</sub>CuO<sub>6+d</sub> as well as semiconducting Ba<sub>0.9</sub>K<sub>0.1</sub>BiO<sub>3</sub> and the strongly magnetoresistant material La<sub>1-x</sub>Sr<sub>x</sub>MnO<sub>3</sub> have been studied by photoelectron spectroscopy. By using the... (More)
In this thesis, the high temperature superconductors (HTSC) Ba<sub>0.6</sub>K<sub>0.4</sub>BiO<sub>3</sub>, La<sub>2</sub>CuO<sub>4+x</sub>, Bi<sub>2</sub>Sr<sub>2</sub>Ca<sub>1-x</sub>Y<sub>x</sub>Cu<sub>2</sub>O<sub> 8+d</sub>, Bi<sub>2</sub>Sr<sub>2</sub>CuO<sub>6+d</sub> as well as semiconducting Ba<sub>0.9</sub>K<sub>0.1</sub>BiO<sub>3</sub> and the strongly magnetoresistant material La<sub>1-x</sub>Sr<sub>x</sub>MnO<sub>3</sub> have been studied by photoelectron spectroscopy. By using the tunability of synchrotron radiation, techniques such as resonant photoemission and x-ray absorption spectroscopy have been applied. The aim of the studies has been to investigate the electronic structure of these compounds with an emphasis on strong electron-electron correlation, the distribution of valence states, band structure effects, the importance of oxygen nonstoichiometry, and the influence of metal overlayers. Experimental results from the high quality single crystals are compared to band structure calculations and atomic absorption calculations.



Resonant photoemission was performed on Ba<sub>1-x</sub>K<sub>x</sub>BiO<sub>3</sub> at photon energies in the vicinity of the Ba 4<i>d</i>, Ba 5<i>p</i> and O 1<i>s</i> core levels. The enhancements seen in the valence band at photon energies corresponding to the Ba 5<i>p</i>-5<i>d</i> excitation are assigned to Ba states. From the resonance at the Ba 4<i>d</i> threshold, Ba states were also identified close to the Fermi level whereas no resonant enhancement was seen for photon energies close to the O <i>K</i> absorption threshold. In addition, angle resolved measurements were used to identify the G and X high symmetry points in Ba<sub>0.6</sub>K<sub>0.4</sub>BiO<sub>3</sub>, and laterally resolved photoelectron microscopy showed a strongly varying Fermi level intensity on a micron length scale.



For Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8+d</sub> and Bi<sub>2</sub>Sr<sub>2</sub>CuO<sub>6+d</sub>, a satellite enhancement was seen for photon energies close to the main oxygen <i>K</i>-edge absorption threshold. From the data, the values of the electron-electron interaction energies <i>U<sub>dd</sub></i> and <i>U<sub>pp</sub></i>, as well as the charge transfer energy D, can be found. The core level shifts and the valence-band shape in cuprate HTSC were also investigated by means of yttrium substitution and surface derived electronic bands.



For La<sub>1-x</sub>Sr<sub>x</sub>MnO<sub>3</sub>, core-level spectroscopy and x-ray absorption measurements indicated that x and temperature dependent changes in the electronic structure can be connected to the various magnetic phases. Temperature dependent resonant photoemission at the O <i>K</i> and Mn <i>L</i><sub>3</sub> edges showed enhanced spectral intensity close to the Fermi level and for photon energies around the Mn <i>L</i> edge, strong enhancements were seen in the valence band.



The importance of small deviations in oxygen content is common for all compounds investigated in this thesis, although x-ray absorption and resonant photoemission measurements showed that O 2<i>p</i> holes play different roles in the doping mechanisms of cuprate and bismuthate high temperature superconductors as well as of magnetoresistant manganites. (Less)
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author
opponent
  • Prof Grepstad, Jostein, Dept. of Physical Electronics, The Norwegian University of Science and Technology, NTNU, N-7034 Trondheim, Norway
organization
publishing date
type
Thesis
publication status
published
subject
keywords
egenskaper (elektriska, supraledare, magnetiska och optiska), magnetisk resonans, X-ray Absorption, Photoelectron Spectroscopy, Resonant Photoemission, Condensed matter:electronic structure, High Temperature Superconductors, Angle Resolved Photoemission, electrical, supraconductors, magnetic and optical properties, magnetic resonance, spectroscopy, spektroskopi, Kondenserade materiens egenskaper:elektronstruktur, relaxation, Fysicumarkivet A:1998:Nylén
pages
140 pages
publisher
Henrik Nylén, Dept. of Synchrotron Radiation Research, Box 118, S-221 00 Lund,
defense location
Lecture hall B, Institute of Physics, Lund
defense date
1998-05-28 10:15
external identifiers
  • other:ISRN: LUNFD6/NFSF--98/1013--SE
ISBN
91-628-2914-9
language
English
LU publication?
yes
id
644e5164-c6f9-409b-8420-4f47df137004 (old id 38757)
date added to LUP
2007-09-28 13:08:52
date last changed
2016-09-19 08:45:04
@phdthesis{644e5164-c6f9-409b-8420-4f47df137004,
  abstract     = {In this thesis, the high temperature superconductors (HTSC) Ba&lt;sub&gt;0.6&lt;/sub&gt;K&lt;sub&gt;0.4&lt;/sub&gt;BiO&lt;sub&gt;3&lt;/sub&gt;, La&lt;sub&gt;2&lt;/sub&gt;CuO&lt;sub&gt;4+x&lt;/sub&gt;, Bi&lt;sub&gt;2&lt;/sub&gt;Sr&lt;sub&gt;2&lt;/sub&gt;Ca&lt;sub&gt;1-x&lt;/sub&gt;Y&lt;sub&gt;x&lt;/sub&gt;Cu&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt; 8+d&lt;/sub&gt;, Bi&lt;sub&gt;2&lt;/sub&gt;Sr&lt;sub&gt;2&lt;/sub&gt;CuO&lt;sub&gt;6+d&lt;/sub&gt; as well as semiconducting Ba&lt;sub&gt;0.9&lt;/sub&gt;K&lt;sub&gt;0.1&lt;/sub&gt;BiO&lt;sub&gt;3&lt;/sub&gt; and the strongly magnetoresistant material La&lt;sub&gt;1-x&lt;/sub&gt;Sr&lt;sub&gt;x&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; have been studied by photoelectron spectroscopy. By using the tunability of synchrotron radiation, techniques such as resonant photoemission and x-ray absorption spectroscopy have been applied. The aim of the studies has been to investigate the electronic structure of these compounds with an emphasis on strong electron-electron correlation, the distribution of valence states, band structure effects, the importance of oxygen nonstoichiometry, and the influence of metal overlayers. Experimental results from the high quality single crystals are compared to band structure calculations and atomic absorption calculations.<br/><br>
<br/><br>
Resonant photoemission was performed on Ba&lt;sub&gt;1-x&lt;/sub&gt;K&lt;sub&gt;x&lt;/sub&gt;BiO&lt;sub&gt;3&lt;/sub&gt; at photon energies in the vicinity of the Ba 4&lt;i&gt;d&lt;/i&gt;, Ba 5&lt;i&gt;p&lt;/i&gt; and O 1&lt;i&gt;s&lt;/i&gt; core levels. The enhancements seen in the valence band at photon energies corresponding to the Ba 5&lt;i&gt;p&lt;/i&gt;-5&lt;i&gt;d&lt;/i&gt; excitation are assigned to Ba states. From the resonance at the Ba 4&lt;i&gt;d&lt;/i&gt; threshold, Ba states were also identified close to the Fermi level whereas no resonant enhancement was seen for photon energies close to the O &lt;i&gt;K&lt;/i&gt; absorption threshold. In addition, angle resolved measurements were used to identify the G and X high symmetry points in Ba&lt;sub&gt;0.6&lt;/sub&gt;K&lt;sub&gt;0.4&lt;/sub&gt;BiO&lt;sub&gt;3&lt;/sub&gt;, and laterally resolved photoelectron microscopy showed a strongly varying Fermi level intensity on a micron length scale.<br/><br>
<br/><br>
For Bi&lt;sub&gt;2&lt;/sub&gt;Sr&lt;sub&gt;2&lt;/sub&gt;CaCu&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;8+d&lt;/sub&gt; and Bi&lt;sub&gt;2&lt;/sub&gt;Sr&lt;sub&gt;2&lt;/sub&gt;CuO&lt;sub&gt;6+d&lt;/sub&gt;, a satellite enhancement was seen for photon energies close to the main oxygen &lt;i&gt;K&lt;/i&gt;-edge absorption threshold. From the data, the values of the electron-electron interaction energies &lt;i&gt;U&lt;sub&gt;dd&lt;/sub&gt;&lt;/i&gt; and &lt;i&gt;U&lt;sub&gt;pp&lt;/sub&gt;&lt;/i&gt;, as well as the charge transfer energy D, can be found. The core level shifts and the valence-band shape in cuprate HTSC were also investigated by means of yttrium substitution and surface derived electronic bands.<br/><br>
<br/><br>
For La&lt;sub&gt;1-x&lt;/sub&gt;Sr&lt;sub&gt;x&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt;, core-level spectroscopy and x-ray absorption measurements indicated that x and temperature dependent changes in the electronic structure can be connected to the various magnetic phases. Temperature dependent resonant photoemission at the O &lt;i&gt;K&lt;/i&gt; and Mn &lt;i&gt;L&lt;/i&gt;&lt;sub&gt;3&lt;/sub&gt; edges showed enhanced spectral intensity close to the Fermi level and for photon energies around the Mn &lt;i&gt;L&lt;/i&gt; edge, strong enhancements were seen in the valence band.<br/><br>
<br/><br>
The importance of small deviations in oxygen content is common for all compounds investigated in this thesis, although x-ray absorption and resonant photoemission measurements showed that O 2&lt;i&gt;p&lt;/i&gt; holes play different roles in the doping mechanisms of cuprate and bismuthate high temperature superconductors as well as of magnetoresistant manganites.},
  author       = {Nylén, Henrik},
  isbn         = {91-628-2914-9},
  keyword      = {egenskaper (elektriska,supraledare,magnetiska och optiska),magnetisk resonans,X-ray Absorption,Photoelectron Spectroscopy,Resonant Photoemission,Condensed matter:electronic structure,High Temperature Superconductors,Angle Resolved Photoemission,electrical,supraconductors,magnetic and optical properties,magnetic resonance,spectroscopy,spektroskopi,Kondenserade materiens egenskaper:elektronstruktur,relaxation,Fysicumarkivet A:1998:Nylén},
  language     = {eng},
  pages        = {140},
  publisher    = {Henrik Nylén, Dept. of Synchrotron Radiation Research, Box 118, S-221 00 Lund,},
  school       = {Lund University},
  title        = {Photoelectron Spectroscopy of High Temperature Superconductors and Related Compounds},
  year         = {1998},
}