Ultrafast dynamics of coherent optical phonon correlated with the antiferromagnetic transition in a hexagonal YMnO3 epitaxial film.

We report on the observation of the coherent optical phonon in a hexagonal YMnO₃ epitaxial film using a reflection-type pump-probe technique at various temperatures, excitation powers, and energies. We detected an oscillatory structure with a frequency of ~5.1 THz, which is assigned to the coherent optical phonon with A₁ symmetry, in a time-domain signal. It was found that the coherent optical phonon can be observed at temperatures from 10K to room temperature, while the oscillation amplitude markedly decreases with an increase in temperature around ~70K corresponding to the Néel temperature. The temperature dependence of the oscillation amplitude indicates that the coherent optical phonon is sensitive to the spin-lattice coupling connected with the antiferromagnetic transition. [ABSTRACT FROM AUTHOR]