13.10.2021

Adam Dubroka:
Photo-induced insulator-to-metal transition in LaCoO3 explored by femtosecond
pump-probe ellipsometry 

Abstract:

Femtosecond lasers are used to probe fast relaxation dynamics in materials
after excitation by a pump pulse in the so-called pump-probe arrangement. We
explore relaxation dynamics in LaCoO3 thin films by femtosecond pump-probe
ellipsometry recently developed in ELI, Břežany. We have observed large
spectral weight shifts corresponding to a pump-induced insulator-to-metal
transition. The excited states initially decay within 200~fs via a fast
relaxation most likely related to an electronic relaxation accompanied by
emission of phonons. We observe in LaCoO3 and also in metallic La0.5Sr0.5CoO3
thin film a significant secondary transient structure on 4--100~ps timescale.
We attribute it to a secondary wave of high-spin states excited by phonons. At
longer delays between 10-1000~ps, the films essentially cool down to the state
before pump via a two-component relaxation process that we tentatively
attribute to thermal diffusion via optical and acoustic phonons.