Optical Absorption in La2−xSrxCuO4 Epitaxial Thin Films
An experimental study on optical absorption is described for La2− x Sr x Cu4 (x = 0 ~ 0.36) c-axis oriented epitaxial films. In addition to the fundamental absorption corresponding to the energy gap of 2 eV, an anomalous absorption band is seen in the optical transmission spectra. This absorption, the intensity of which increases with Sr doping, implies Sr doping induces electronic states within the gap of La2CuO4. With further Sr doping, the density of states forms a band about 1 eV wide and centered at about 0.5 eV above the top of the original valence band. This emerging density of states within the gap is totally at variance with the conventional rigid band model, and seems to be inherent to the high T c superconductors.
KeywordsFermi Level Optical Absorption Doping Level Electron Energy Loss Spectroscopy Epitaxial Film
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