Abnormal phase flip in the coherent phonon oscillations of Ca2RuO4

Min Cheol Lee, Choong H. Kim, Inho Kwak, J. Kim, S. Yoon, Byung Cheol Park, Bumjoo Lee, F. Nakamura, C. Sow, Y. Maeno, T. W. Noh, K. W. Kim

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Abstract

We employ an optical pump-probe technique to study coherent phonon oscillations in Ca2RuO4. We find that oscillation amplitude of an Ag symmetric phonon mode is strongly suppressed at 260 K, a putative transition point of orbital ordering. The oscillation also shows a gradual but huge change in its phase, such that the oscillation even flips over with a 180 change across the temperature. Density functional theory calculations indicate that the Ag phonon has an eigenmode of octahedral distortion with conventional tilting along the a axis and antipolar distortion of apical oxygen. Careful inspection of the lattice captures an unusually large antipolar distortion in low-temperature structures, which may play a crucial role for the phase transition at 260 K.

Original languageEnglish
Article number161115
JournalPhysical Review B
Volume98
Issue number16
DOIs
StatePublished - 17 Oct 2018

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