Atomic resolution mapping of the excited-state electronic structure ofCu2Owith time-resolved x-ray absorption spectroscopy

Abstract

We have used time-resolved soft x-ray spectroscopy to investigate the electronic structure of optically excited cuprous oxide at the $\text{O}\text{ }K$ edge and the $\text{Cu}\text{ }{L}_{3}$ edge. The 400 nm optical excitation shifts the Cu and O absorptions to lower energy, but does not change the integrated x-ray absorption significantly for either edge. The constant integrated x-ray absorption cross-section indicates that the conduction-band and valence-band edges have very similar $\text{Cu}\text{ }3d$ and $\text{O}\text{ }2p$ orbital contributions. The 2.1 eV optical band gap of ${\text{Cu}}_{2}\text{O}$ significantly exceeds the one eV shift in the $\text{Cu}\text{ }{L}_{3}$- and $\text{O}\text{ }K$-edges absorption edges induced by optical excitation, demonstrating the importance of core-hole excitonic effects and valence electron screening in the x-ray absorption process.