Photo-induced insulator-to-metal transition and coherent acoustic phonon propagation in LaCoO${}_3$ thin films explored by femtosecond pump-probe ellipsometry

Abstract

We have studied ultrafast dynamics of thin films of LaCoO${}_3$ and La${}_{0.5}$Sr${}_{0.5}$CoO${}_3$ with femtosecond pump-probe ellipsometry in the energy range of 1.6-3.4 eV. We have observed a large pump-induced transfer of spectral weight in LaCoO${}_3$ that corresponds to an insulator-to-metal transition. The photo-induced metallic state initially relaxes via a fast process with a decay constant of about 200 fs. Both LaCoO${}_3$ and La${}_{0.5}$Sr${}_{0.5}$CoO${}_3$ exhibit a significant secondary transient structure in the 1-30 ps range. Results of measurements on films with different thicknesses demonstrate that it corresponds to a propagation of an acoustic strain pulse. On timescales longer than 100 ps, heat diffusion to the substrate takes place that can be modelled with a bi-exponential decay.

8 pages, 4 figures

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• The spin state transition in LaCoO${}_3$; revising a revision
• Spin state transition and covalent bonding in LaCoO3
• Dimensionality Control of d-orbital Occupation in Oxide Superlattices
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Cited by in corpus (1)

• Optical signatures of strain-induced ferromagnetism in LaCoO${}_3$ thin film