VUV-PHOTOEMISSION STUDY OF (LA1-XSRX)2CUO4-DELTA SINGLE-CRYSTALS AND THEIR SURFACE DEGRADATION

We have measured the valence-band photoelectron spectra of (La1-xSrx)2 CuO4-delta single crystals. Spectra obtained at low temperatures (30-8 0 K) are similar to each other as well as the results reported so far: The intensity at the Fermi level is quite low and the valence-band ma ximum is shifted to higher binding-energy than what the energy-band ca lculation predicts. At room temperature the intensity of the 3 eV band is reduced rapidly while the specimen is kept in dark, while it shows a quick recovery when the specimen is exposed to the excitation light for photoelectron measurements. This suggests that a photo-assisted p rocess may take part in this phenomenon. Some possible mechanisms for the photo-induced changes are discussed.