Electron-energy-loss spectroscopy of oxide superconductor bÍ2sr2cacu208

Transmission electron-energy-loss spectra of the oxide superconductor BÍ2Sr2CaCu2 0s have been taken from perfect crystalline areas (100 nm</)) in an energy range of 0-60 eV at temperatures of 30 K, 100 K and 300 K. A peak at about 0.6 eV was observed at these temperatures instead of a peak at about 1 eV which was reported to be a free-carrier plasmon peak. The dielectric function derived from the loss-function indicates that the peak at about 0.6 eV can be attributed not to a collective excitation (plasmon) but to an interband transition. The electron density which contributes to the peak has been calculated to be 2 x 10^^ electron/cm^. The peaks and shoulders of the spectra (the loss-function) are assigned to individual interband transitions. The temperature dependence of £2 has been found around 2.5 eV and 5.5 eV.