https://doi.org/10.1051/epjconf/20134104021
Interband excitation and carrier relaxation as displacive driving force for coherent phonons
1 Technical University Munich, Department of Physics, 85748 Garching, Germany
2 Max Planck Institute for Quantum Optics, 85748 Garching, Germany
3 Fritz Haber Institute of the Max Planck Society, 14195 Berlin, Germany
4 University Kassel, Theoretical Physics Department, 34132 Kassel, Germany
5 Ludwig Maximilian University Munich, Faculty of Physics, 85748 Garching, Germany
We report on displacive excitation of large amplitude coherent lattice motions in TiO2 under resonant conditions using sub-6-femtosecond UV pulses. Calculations of non-equilibrium potential energy surfaces reveal a new displacive mechanism for the coherent phonon generation, where a unidirectional displacement of the phonon potential occurs both instantaneously due to carrier excitation and dynamically due to cooling of the hot photo-excited carriers. The carrier cooling dynamics in TiO2 are faster than the phonon period, resulting in an initially anharmonic lattice motion. This effect manifests itself in an effective phase shift of the coherent phonon oscillation, in good agreement between our experiments and the calculations.
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