Ultrafast spectral weight transfer inRBaCo2O6−δ(R=Sm, Gd, and Tb): Role of electronic correlation in a photoinduced phase transition

Abstract

We performed femtosecond reflection spectroscopy on a series of A-site ordered perovskite-type cobalt oxide $R$BaCo${}_{2}$O${}_{6\ensuremath{-}\ensuremath{\delta}}$ ($R=\text{Sm}$, Gd, and Tb) crystals, in which the electronic transfer was controlled by $R$. The transient reflectivity and the optical conductivity [${\ensuremath{\sigma}}^{\mathrm{PI}}(\ensuremath{\omega})$] obtained by a Kramers-Kronig analysis showed an ultrafast change within a time resolution ($\ensuremath{\approx}$150 fs) at room temperature and the appearance of signals of a hidden state that were different from the high-temperature metallic state. The transferred spectral weight in ${\ensuremath{\sigma}}^{\mathrm{PI}}(\ensuremath{\omega})$ upon photoexcitation sensitively depended on the $R$ species, indicating an important role of electronic correlation in the photoexcited state.