Abstract
The electronic structure and dielectric functions of single crystallites of the infinite-layer compound (Sr[sub 1[minus][ital x]]Ca[sub [ital x]])[sub [ital y]]CuO[sub 2] ([ital y]=0.90, [ital x]=0.3) are investigated by transmission-electron-energy-loss spectroscopy with a cold-field emission-gun TEM. The band gap along the [ital c] axis is estimated to be significantly greater than in the [ital aa] plane, which suggests anisotropic electronic properties. Unlike other cuprates, oxygen core-loss spectra of this compound display two distinct preedge peaks. A close correlation was observed between the valence-band excitations below 10 eV in the [ital aa] plane and the oxygen [ital K] core-loss fine structure. The [similar to]2 eV excitation in the valence-band spectrum is associated with a transition from the lower Hubbard band to the upper Hubbard band and is detected only in the [ital aa] plane. This excitation coincides with the first preedge peak in O [ital K] core-loss spectra, which is assigned to a transition from the O 1[ital s] state to the upper Hubbard band. The results are consistent with the band-structure calculations, for the infinite-layer compound, which indicate strong Cu 3[ital d]--O 2[ital p] hybridization within the [ital aa] plane, but little overlap of the wave function along the [ital c]more » axis.« less
Published Version
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