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O: Fachverband Oberflächenphysik
O 67: Ultrafast Electron Dynamics II
O 67.1: Vortrag
Mittwoch, 19. März 2025, 15:00–15:15, H11
Polaron formation in NiO analysed by transient absorption spectroscopy — •Mahendra Kabbinahithlu1, Björn Sothmann1, Fred Hucht1, Sergey Kovalenko2, Tobias Lojewski1, Nico Rothenbach1, Katharina Ollefs1, Heiko Wende1, Uwe Bovensiepen1, Julia Stähler2, and Andrea Eschenlohr1 — 1Universität Duisburg-Essen, Fakultät für Physik und Center for Nanointegration (CENIDE), Lotharstraße 1, 47057 Duisburg, Germany — 2Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Straße 2, 12489 Berlin, Germany
Polaron formation is the process by which free electrons in a material find a lower energy localized state by distorting their surrounding lattice. The polaron formation timescales and its fluence dependent dynamics in nickel oxide (NiO) from time-resolved optical absorption studies is discussed here.
NiO is pumped above the band gap with 3.98 eV energy photons, and is probed using a time-delayed supercontinuum. The time-resolved absorption spectrum shows negative ground state bleach and positive excited state absorption and in addition, a time-delayed and energy separated appearance of a positive feature at 3.35 eV that is discussed as the signature of polaron formation. With increasing fluence,the build-up time of this 3.35 eV signature decreases from 4 ps down to 1.1 ps, indicating the transition from isolated polarons to the formation of a polaron band. The spectrally distinct transition between low fluence and high fluence regimes is used to estimate the polaron size and the dynamics is modelled by coupled rate equations.
Keywords: NiO; Time-resolved optical spectroscopy; Polarons