Transmission High‐Energy Electron Energy Loss Spectrometry (EELS) Analysis of Hole Formation and Charge Transfer in p‐type Doped Cuprate Superconductors

Abstract

The technique of transmission high‐energy electron energy loss spectrometry (EELS) in TEM has been applied to analyze the formation of charge carriers (holes) and charge transfer in p‐type doped cuprate superconductors. The O‐K absorption edges of these compounds exhibit a distinct pre‐edge feature which is related to the formation of holes on oxygen sites. The newly discovered Ga‐based cuprate superconductors display additional significant spectral features. O‐K absorption edge fine structure analysis reveals two types of holes in this system, one induced by hole doping alone and the other by high‐pressure oxygenation treatment. Only the second type of hole appears to be associated with the occurrence of superconductivity. The Cu L3 edge of the doped and oxygenated compounds also exhibits a pronounced shoulder on the higher‐energy side of the Cu L3 edge which represents the charge transfer between copper and oxygen. EELS absorption data are consistent with the doped charge‐transfer insulator or Mott‐Hubbard model description of the electronic states. Necessary experiments to distinguish between the above two models are also suggested.