Photoinduced Absorption in the La2−xSrxCuO4–5 System: 2 eV Bandgap and Long-Lived Defect States

Abstract

The discovery of high temperature superconductivity in the La-Ba-Cu-O system [1] has stimulated extensive study of these and related materials. A number of band structure calculations [2,3] have been performed for these materials to explain their electronic structure, and models invoking electron-phonon, electron-electron, or excitonic mechanisms have been proposed for the unusually high Tc [4–9]. Several optical studies were performed[10–12] on sintered pellets or single crystals in an attempt to reveal the electronic structure. It is important to understand the electronic structure of the parent La2CuO4 compound and the defect states that are introduced into the system upon addition or removal of electrons- accomplished by doping or photoexcitation-as they are critical in understanding the mechanism for superconductivity.