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

TL;DR

This study uses femtosecond spectroscopy to reveal ultrafast spectral weight transfer and hidden states in RBaCo2O6-delta cobalt oxides, highlighting the role of electronic correlation in photoinduced phase transitions.

Contribution

It demonstrates the ultrafast spectral weight transfer and the influence of rare-earth elements on electronic correlation effects during photoexcitation.

Findings

Ultrafast change in optical properties within 150 fs.

Detection of a hidden state distinct from the high-temperature metallic phase.

Spectral weight transfer depends on the rare-earth element R.

Abstract

We performed femtosecond reflection spectroscopy on a series of perovskite-type cobalt oxide $R$BaCo$_2$O$_{6-\delta}$ ($R$=Sm, Gd, and Tb) crystals, in which the electronic transfer was controlled by $R$. The transient reflectivity and the optical conductivity ($\sigma^{\rm PI}(\omega)$) 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 $\sigma^{\rm PI}(\omega)$ upon photoexcitation sensitively depended on the $R$-species, indicating an important role of electronic correlation in the photoexcited state.