Photoemission measurements of transition-metal oxides under laser illumination

Abstract

The effects of photoexcitation on Sr 14−xCa xCu 24O 41 and La 2−2xSr 1+2xMn 2O 7 single crystals were measured via X-ray photoemission spectroscopy. Changes observed in the Sr 14−xCa xCu 24O 41 Cu 2p core-level line shape indicate that the cleaved surface is surprisingly unstable under vacuum and that changes in the surface stoichiometry are easily obtained with laser ablation. In La 2−2xSr 1+2xMn 2O 7, the O 1s core-level peak binding energy irreversibly increases upon optical excitation. The magnitude of the increase depends on the sample hole doping and is observed to be largest in a x = 0.5 sample, where phase competition between electronic ordered states is strongest. It appears that the photoinduced electronic structural change is permanent due to stabilization by strong electron-lattice coupling.