Berlin 2018 – wissenschaftliches Programm

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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 27: Postersession KFM

KFM 27.11: Poster

Donnerstag, 15. März 2018, 15:00–17:00, Poster E

Dynamics of small polarons in the limit of high charge carrier densities — •Thorben Groven, Simon Messerschmidt, and Mirco Imlau — Department of Physics, Osnabrück University, Barbarastr. 7, 49076 Osnabrück, Germany

Small strong-coupling polarons take a crucial part in optical processes [Imlau, M. et al., Appl. Phys. Rev. 2 (2015)]; therefore, polaron dynamics in dependency of the excitation wavelength are of vital interest. Up to now, polaron excitation has been investigated in the vis-spectral range via two-photon absorption (TPA) whereas polaron dynamics initiated by higher photon energies are largely unknown.

We have addressed this question by performing systematic studies under deep UV-pulse excitation at 355 nm and probed with different cw-lasers via transient absorption spectroscopy. Optical excitation and recombination of small polarons is analyzed in terms of pump-intensity and temperature in congruent, Mg-, and Fe-doped lithium niobate (LN). At 355 nm, the bound/free polaron formation probability for congruent and Mg-doped LN increases towards the UV region because of a growing TPA coefficient, whereas iron-doped LN exhibits a decreased bound polaron formation probability altogether compared to an excitation at 532 nm due to an altered excitation path. Latter can be explained by a single photon absorption (SPA) from the valence band into the Fe³⁺-state forming hole-polarons and Fe²⁺. Furthermore, SPA quenches TPA and therefore, band to band transitions are suppressed. Financial support by the DFG (IM 37/5-2, INST 190/165-1 FUGG) is gratefully acknowledged.