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Ultrafast Evolution of the Excited-State Potential Energy Surface of TiO2 Single Crystals Induced by Carrier Cooling

MPG-Autoren
http://pubman.mpdl.mpg.de/cone/persons/resource/persons21937

Paarmann,  Alexander
Physical Chemistry, Fritz Haber Institute, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons21497

Ernstorfer,  Ralph
Physical Chemistry, Fritz Haber Institute, Max Planck Society;

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Volltexte (frei zugänglich)

PhysRevLett.110.067402.pdf
(Verlagsversion), 538KB

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Zitation

Bothschafter, E. M., Paarmann, A., Zijlstra, E. S., Karpowicz, N., Garcia, M. E., Kienberger, R., et al. (2013). Ultrafast Evolution of the Excited-State Potential Energy Surface of TiO2 Single Crystals Induced by Carrier Cooling. Physical Review Letters, 110(6): 067402. doi:10.1103/PhysRevLett.110.067402.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-000E-E36E-D
Zusammenfassung
We investigate the influence of carrier cooling dynamics in TiO2 on the excited-state potential energy surface along the A1g optical phonon coordinate after above band-gap excitation using ultrashort ultraviolet pulses. The large amplitude coherent oscillation observed in a pump-probe transient reflectivity measurement shows a phase shift of -0.2π with respect to a purely instantaneous displacive excitation. The dynamic evolution of the potential energy surface minimum of the coherent phonon coordinate is explored using accurate density functional theory calculations, which confirm a shift of the potential energy surface minimum upon resonant laser excitation and reveal a significant positive contribution to the displacive force due to the cooling of the excited hot electron-hole plasma. We show that this noninstantaneous effect can quantitatively explain the experimentally observed phase using reasonable assumptions for the parameters characterizing the excited carriers. Our work demonstrates that the fast equilibration dynamics of laser-excited nonequilibrium carrier populations can have a pronounced effect on the initial structural response of crystalline solids.