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DOE OSTI · 3375328

Coherent and Dynamic Small Polaron Delocalization in CuFeO 2

Mendes, Jocelyn L. [California Institute of Technology (CalTech), Pasadena, CA (United States)] (ORCID:0000000338500724)·Bhattacharyya, Srijan [University of Colorado, Boulder, CO (United States)]·Huang, Chengye [University of California, Berkeley, CA (United States)]·Michelsen, Jonathan M. [California Institute of Technology (CalTech), Pasadena, CA (United States)] (ORCID:0000000274205610)·Klein, Isabel M. [California Institute of Technology (CalTech), Pasadena, CA (United States)] (ORCID:0000000161346732)·Babbe, Finn [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:000000029131638X)·Sayer, Thomas [University of Colorado, Boulder, CO (United States); Durham University (United Kingdom)] (ORCID:0000000161560835)·Li, Tianchu [University of Colorado, Boulder, CO (United States)]·Cooper, Jason K. [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)]·Liu, Hanzhe [Purdue University, West Lafayette, IN (United States)]·Ginsberg, Naomi S. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000256603586)·Montoya-Castillo, Andrés [University of Colorado, Boulder, CO (United States)] (ORCID:0000000330373695)·Cushing, Scott K. [California Institute of Technology (CalTech), Pasadena, CA (United States)] (ORCID:0000000335382259)
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Abstract

Small polarons remain a bottleneck in realizing efficient transition metal oxide devices. Routes to engineer small polaron coupling to electronic states and lattice modes to control carrier localization remain unclear. Here, we measure small polaron formation in CuFeO 2 using transient extreme ultraviolet reflection spectroscopy and compare to theoretical predictions in realistically parametrized Holstein models, demonstrating that polaron localization depends on coupling to high-frequency versus low-frequency phonon bath components. We measure small polaron formation on a comparable ∼100 fs timescale to other Fe(III) compounds. Dynamic delocalization of the polaron follows formation through a coherent lattice expansion between Fe–O layers and charge-sharing with surrounding Fe(IV) states. Simulations reveal two major factors dictate polaron formation timescales: phonon density and reorganization energy distributions between acoustic and optical modes, matching experimental findings. Our work shows how electronic-structural coupling in a polaron-host material can be leveraged to suppress polaronic effects for various applications.

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Mendes, Jocelyn L. [California Institute of Technology (CalTech), Pasadena, CA (United States)] (ORCID:0000000338500724), Bhattacharyya, Srijan [University of Colorado, Boulder, CO (United States)], Huang, Chengye [University of California, Berkeley, CA (United States)], Michelsen, Jonathan M. [California Institute of Technology (CalTech), Pasadena, CA (United States)] (ORCID:0000000274205610), Klein, Isabel M. [California Institute of Technology (CalTech), Pasadena, CA (United States)] (ORCID:0000000161346732), Babbe, Finn [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:000000029131638X), Sayer, Thomas [University of Colorado, Boulder, CO (United States); Durham University (United Kingdom)] (ORCID:0000000161560835), Li, Tianchu [University of Colorado, Boulder, CO (United States)], Cooper, Jason K. [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)], Liu, Hanzhe [Purdue University, West Lafayette, IN (United States)], Ginsberg, Naomi S. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000256603586), Montoya-Castillo, Andrés [University of Colorado, Boulder, CO (United States)] (ORCID:0000000330373695), Cushing, Scott K. [California Institute of Technology (CalTech), Pasadena, CA (United States)] (ORCID:0000000335382259). 2026-01-02. Coherent and Dynamic Small Polaron Delocalization in CuFeO 2. https://doi.org/10.1021/acs.jpclett.5c03430

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