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arXiv · 2201.02525

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

M. Zahradnik·M. Kiaba·S. Espinoza·M. Rebarz·J. Andreasson·O. Caha·F. Abadizaman·D. Munzar·A. Dubroka
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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.

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M. Zahradnik, M. Kiaba, S. Espinoza, M. Rebarz, J. Andreasson, O. Caha, F. Abadizaman, D. Munzar, A. Dubroka. 2022-01-07. Photo-induced insulator-to-metal transition and coherent acoustic phonon propagation in LaCoO$_3$ thin films explored by femtosecond pump-probe ellipsometry. https://doi.org/10.1103/physrevb.105.235113

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