Kavli Affiliate: Scott K. Cushing
| First 5 Authors: Jocelyn L. Mendes, Hyun Jun Shin, Jae Yeon Seo, Nara Lee, Young Jai Choi
| Summary:
Controlling the effects of photoexcited polarons in transition metal oxides
can enable the long timescale charge separation necessary for renewable energy
applications as well as controlling new quantum phases through dynamically
tunable electron-phonon coupling. In previously studied transition metal
oxides, polaron formation is facilitated by a photoexcited ligand-to-metal
charge transfer (LMCT). When the polaron is formed, oxygen atoms move away from
iron centers, which increases carrier localization at the metal center and
decreases charge hopping. Studies of yttrium iron garnet and erbium iron oxide
have suggested that strong electron and spin correlations can modulate
photoexcited polaron formation. To understand the interplay between strong spin
and electronic correlations in highly polar materials, we studied gadolinium
iron oxide (GdFeO3), which selectively forms photoexcited polarons through an
Fe-O-Fe superexchange interaction. Excitation-wavelength-dependent transient
extreme ultraviolet (XUV) spectroscopy selectively excites LMCT and
metal-to-metal charge transfer transitions (MMCT). The LMCT transition
suppresses photoexcited polaron formation due to dominant Hubbard interactions,
while MMCT transitions result in photoexcited polaron formation within
~373+/-137 fs due to enhanced superexchange interactions. Ab initio theory
demonstrates that both electron and hole polarons localize on iron centers
following MMCT. In addition to understanding how strong electronic and spin
correlations can control strong electron-phonon coupling, these experiments
separately measure electron and hole polaron interactions on neighboring metal
centers for the first time, providing insight into a large range of
charge-transfer and Mott-Hubbard insulators.
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