Probing Charge on Cu in Oxide Superconductors
The non-destructive measurement of charge on an ion in a solid has always been a source of great controversy. In this chapter, we will review how x-ray absorption spectroscopy addresses this issue. We will describe the underlying principles of the technique, list some recent experiments, and try to explain the controversial aspects. A new method of evaluation of the position of the absorption edge will be introduced, and its relation to the Mulliken populations determined by discrete variational method for calculating orbital states of a molecular cluster will be discussed. We will then show how x-ray absorption spectroscopy can probe variations in effective charge on atoms as a result of chemical doping. Finally, we will point out some newer developments as a result of using polarized x-rays and oriented crystals.
KeywordsAbsorption Edge Effective Charge Oxide Superconductor Chemical Doping Discrete Variational Method
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