Monitoring ultrafast metallization in LaCoO3 with femtosecond soft x-ray spectroscopy

The study of ultrafast dynamics is a new tool to understand and control the properties of correlated oxides. By enhancing some properties and realizing new dynamically excited phrases, this tool has opened new routes for technological applications. LaCoO3 is one paradigmatic example where the strong electron, spin, and lattice coupling induced by electronic correlations results in a low-temperature spin transition and a high-temperature semiconductor-to-metal transition that is still not completely understood. Here, we monitor ultrafast metallization in LaCoO3 using time-resolved soft x-ray reflectivity experiments. While the process is entangled at the Co L-3 edge, the time information of the different channels is decrypted at different resonant energies of the O K edge. Metallization is shown to occur via transient electronic, spin, and lattice separation. Our results agree with the thermodynamical model and demonstrate the potential of femtosecond soft x-ray experiments at the O K edge to understand correlated oxides. We thank Karsten Holldack, Niko Pontius, and Christian Schuessler-Langeheine, for experimental support at the FemtoSpeX facility during the experiments. We acknowledge Alexander Folisch for supporting the realization of the experiments at the FEMTOSPEX and Kurt Ament for editing the manuscript. M. I. acknowledges BMBF Grant no. 05K12GU2 for financial support.