Ultrafast Spectral Weight Transfer in RBaCo2O6-delta (R=Sm, Gd, and Tb): A Role of Electronic Correlation in Photoinduced Phase Transition

Abstract

We performed femtosecond reflection spectroscopy on a series of perovskite-type cobalt oxide $R$BaCo${}_2$O${}_{6-\hat{I}´}$ ($R$=Sm, Gd, and Tb) crystals, in which the electronic transfer was controlled by $R$. The transient reflectivity and the optical conductivity ($\ddot{I}{ƒ}^{\mathrm{PI}}(\ddot{I}‰)$) obtained by Kramers-Kronig analysis showed an ultrafast change within a time resolution ($\approx 150$ fs) at room temperature and the appearance of signals of a hidden state different from the high temperature metallic state. The transferred spectral weight in $\ddot{I}{ƒ}^{\mathrm{PI}}(\ddot{I}‰)$ upon photoexcitation sensitively depended on the $R$-species, indicating an important role of electronic correlation in the photoexcited state.