Persistent Photo-Enhancement of Molecular Orbital Excitations in the Kondo Insulator FeSb2
Abstract
When insulators are excited by photons with above-gap energies, photo-doped carriers are transiently generated. Typically, orbital excitations weaken and broaden due to increased screening by these transient carriers, followed by a few-ps recovery via phonon thermalization. Here we report the observation of anomalous dynamics of many-body molecular orbital excitations in the narrow-gap Kondo insulator FeSb2. In the pumped X-ray absorption spectra following excitation with 1~μm photons, we observe a transient transfer of absorption intensity from the delocalized states at the main absorption peak to the localized molecular orbital states at the pre-edge. At the resonance of the low-energy molecular orbital excitations, the pumped resonant inelastic X-ray spectra show an approximately 30\% intensity increase at a pump fluence of 11 mJ/cm2 concomitant with the emergence of an energy gain feature. While the energy gain feature disappears after about 1-2~ps, the increased molecular orbital excitation intensities partially persist for at least 50~ps with no discernible energy shift. These observations require the invocation of a many-body excitation picture beyond single particle population changes.
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BibTeX
@misc{xu2026persistent,
title = {{Persistent Photo-Enhancement of Molecular Orbital Excitations in the Kondo Insulator FeSb$_2$}},
author = {Ke-Jun Xu and Nathan Giles-Donovan and Paulina Majchrzak and Abhi Suthar and Matthias Hepting and Marco Trento and Giacomo Ghiringhelli and Elizabeth Skoropata and Hiroki Ueda and Eugenio Paris and Biaolong Liu and Elia Razzoli and Wei-Sheng Lee and Thomas P. Devereaux and Zhi-Xun Shen and Dung-Hai Lee and Robert J. Birgeneau},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.27630},
eprint = {2610.27630},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.27630},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Persistent Photo-Enhancement of Molecular Orbital Excitations in the Kondo Insulator FeSb_2
AU - Ke-Jun Xu
AU - Nathan Giles-Donovan
AU - Paulina Majchrzak
AU - Abhi Suthar
AU - Matthias Hepting
AU - Marco Trento
AU - Giacomo Ghiringhelli
AU - Elizabeth Skoropata
AU - Hiroki Ueda
AU - Eugenio Paris
AU - Biaolong Liu
AU - Elia Razzoli
AU - Wei-Sheng Lee
AU - Thomas P. Devereaux
AU - Zhi-Xun Shen
AU - Dung-Hai Lee
AU - Robert J. Birgeneau
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2610.27630
UR - https://arxiv.org/abs/2610.27630
AB - When insulators are excited by photons with above-gap energies, photo-doped carriers are transiently generated. Typically, orbital excitations weaken and broaden due to increased screening by these transient carriers, followed by a few-ps recovery via phonon thermalization. Here we report the observation of anomalous dynamics of many-body molecular orbital excitations in the narrow-gap Kondo insulator FeSb_2. In the pumped X-ray absorption spectra following excitation with 1~μm photons, we observe a transient transfer of absorption intensity from the delocalized states at the main absorption peak to the localized molecular orbital states at the pre-edge. At the resonance of the low-energy molecular orbital excitations, the pumped resonant inelastic X-ray spectra show an approximately 30\% intensity increase at a pump fluence of 11 mJ/cm^2 concomitant with the emergence of an energy gain feature. While the energy gain feature disappears after about 1-2~ps, the increased molecular orbital excitation intensities partially persist for at least 50~ps with no discernible energy shift. These observations require the invocation of a many-body excitation picture beyond single particle population changes.
ER -