Abstract
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.
Highlights
Transition metal oxides have attracted much attention due to the complex and strong interaction amongst the charge carriers, as well as between carriers and the lattice, such that small perturbations can lead to dramatic modification of the material properties
We report on displacive excitation of large amplitude coherent lattice motions in TiO2 under resonant conditions using sub-6-femtosecond UV pulses
A typical phenomenon is the significant deformation of the lattice potential following electronic excitations, often studied by displacive excitation of coherent lattice motions by femtosecond optical pulses
Summary
Transition metal oxides have attracted much attention due to the complex and strong interaction amongst the charge carriers, as well as between carriers and the lattice, such that small perturbations can lead to dramatic modification of the material properties. The magnitude of the displacive force is assumed to be proportional to the excited charge density [1], and relaxation of the electronic excited state acts to destroy the coherence of the lattice motion. We observe a significant dependence of the A1 potential displacement on the electronic temperature such that the rapid carrier cooling acts as an additional driving force for the coherent phonon. This effect is discussed as a possible cause of the experimentally observed phonon phase shift
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
