Center for Molecular Spectroscopy and Dynamics

IBS CMSD Seminar

Prof. Ye-Jin Kim

September 25(Wed) - September 25(Wed), 2024

16:00~17:00

Seminar Room B (119)

ABSTRACT

Over the past few decades, tabletop time-resolved X-ray spectroscopy has seen advancements, offering precise probing of elements, charge carriers, and oxidation states, along with flexibility for instrumental modifications. Employing attosecond pulse trains or extreme ultraviolet (XUV) probes produced by gas-phase high-harmonic generation enabled the exploration of electronic localization dynamics with millielectronvolt resolution and high surface sensitivity, taking advantage of optical transitions from shallow core levels. [1]. Polarons, which are localized electron-lattice interactions, form in transition metal oxides through coupling with optical phonons, particularly in the adiabatic regime. The lattice reorganization energy in this case is so large that the first electron–optical phonon scattering event creates a small polaron without requiring extensive carrier thermalization [2]. Using the transient XUV absorption/reflection spectroscopy, it was observed for the first time that disrupting the iron-centered octahedra in the rare-earth orthoferrite ErFeO3 leads to the formation of nonadiabatic small polarons [3]. Coherent charge hopping between neighboring Fe3+ and Fe2+ sites persists for several picoseconds before the polaron fully forms. The formation time is an order of magnitude longer than previous measurements, indicating a shallow potential well, even in the excited state. This highlights the importance of accounting for dynamic electron-electron correlations, along with electron-phonon–induced lattice changes, in understanding polaronic behavior for the applications in transport, catalysis, and photoexcitation, which can be uniquely measured with the attosecond XUV probe.

References

[1] H. Liu, et al. Element-specific electronic and structural dynamics using transient XUV and soft X-ray spectroscopy, Chem. 7, 2569–2584 (2021)

[2] L. M. Carneiro, et al. Excitation-wavelength-dependent small polaron trapping of photoexcited carriers in α-Fe2O3, Nat. Mat. 16, 819–825 (2017)

[3] Y.-J. Kim, et al. Coherent charge hopping suppresses photoexcited small polarons in ErFeO3 by antiadiabatic formation mechanism, Sci. Adv. 10, adk4282 (2024)