Ultrafast dynamics of coherent optical phonon correlated with the antiferromagnetic transition in a hexagonal YMnO_3 epitaxial film

摘要

We report on the observation of the coherent optical phonon in a hexagonal YMnO_3 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 A_1 symmetry, in a time-domain signal. It was found that the coherent optical phonon can be observed at temperatures from 10 K to room temperature, while the oscillation amplitude markedly decreases with an increase in temperature around ∼70 K 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.