Kavli Affiliate: Naomi S. Ginsberg
| First 5 Authors: Jocelyn L. Mendes, Jocelyn L. Mendes, , ,
| Summary:
Small polarons remain a significant bottleneck in the realization of
efficient devices using transition metal oxides. Routes to engineer small
polaron coupling to electronic states and lattice modes to control carrier
localization remain unclear. Here, we measure the formation of small polarons
in CuFeO$_2$ using transient extreme ultraviolet reflection spectroscopy and
compare it to theoretical predictions in realistically parameterized Holstein
models, demonstrating that polaron localization depends on its coupling to the
high-frequency versus low-frequency components of the phonon bath. We measure
that small polaron formation occurs on a comparable ~100 fs timescale to other
Fe(III) compounds. After formation, a dynamic delocalization of the small
polaron occurs through a coherent lattice expansion between Fe-O layers and
charge-sharing with surrounding Fe(IV) states. Our simulations of polaron
formation dynamics reveal that two major factors dictate polaron formation
timescales: phonon density and reorganization energy distributions between
acoustic and optical modes, matching experimental findings. Our work provides a
detailed, real-time observation of how electronic-structural coupling in a
polaron-host material can be leveraged to suppress polaronic effects for
various applications.
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