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Vibronic Excitation Dynamics in Orbitally Degenerate Correlated Electron System

Orbital-lattice coupled excitation dynamics in orbitally degenerate correlated systems are examined. We present a theoretical framework, where both local vibronic excitations and superexchange-type inter-site interactions are dealt with on an equal footing. We generalize the spin-wave approximation so as to take local vibronic states into account. Present method is valid from weak to strong Jahn-Teller coupling magnitudes. Two characteristic excitation modes coexist; a low-energy dispersive mode and high-energy multi-peak mode. These are identified as a collective vibronic mode, and Flanck-Condon excitations in a single Jahn-Teller center modified by the inter-site interactions, respectively. Present formalism covers vibronic dynamics in several orbital-lattice coupled systems.