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Schlagwörter:
PACS numbers: 78.47.J-, 63.20.kk, 71.70.Gm, 75.47.Lx
Zusammenfassung:
Coherent lattice vibrations are excited and probed with pulses of 10 fs duration in LaMnO3. The measured frequencies correspond to those of Jahn-Teller stretching and of out-of phase rotations of the oxygen octahedra. Surprisingly, the amplitude and damping rate of both modes exhibit a sharp discontinuity at the Néel temperature, highlighting nontrivial coupling between light, lattice, and magnetic structure. We explain this effect by applying the Goodenough-Kanamori rules to the excited state of LaMnO3, and note that charge transfer can invert the sign of the semicovalent exchange interaction, which in turn perturbs the equilibrium bond lengths.