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arXiv · 2307.05139

Coherent phonon and unconventional carriers in the magnetic kagome metal Fe$_3$Sn$_2$

M. V. Gonçalves-Faria·A. Pashkin·Q. Wang·H. C. Lei·S. Winnerl·A. A. Tsirlin·M. Helm·E. Uykur
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Abstract

Temperature- and fluence-dependent carrier dynamics of the magnetic Kagome metal Fe$_3$Sn$_2$ were studied using the ultrafast optical pump-probe technique. Two carrier relaxation processes ($\tau_1$ and $\tau_2$) and a laser induced coherent optical phonon were observed. By using the two-temperature model for metals, we ascribe the shorter relaxation $\tau_1$ (~1 ps) to hot electrons transferring their energy to the crystal lattice via electron-phonon scattering. $\tau_2$ (~25 ps), on the other hand, cannot be explained as a conventional process and is attributed to the unconventional (localized) carriers in the material. The observed coherent oscillation is assigned to be a totally symmetric A$_{1g}$ optical phonon dominated by Sn displacements out of the Kagome planes, and possesses a prominently large amplitude, on the order of 10$^{-3}$, comparable to the maximum of the reflectivity change ($\Delta$R/R). This amplitude is equivalent to charge-density-wave (CDW) systems, although no signs of such an instability were hitherto reported in Fe$_3$Sn$_2$. Our results set an unexpected connection between Fe$_3$Sn$_2$ and kagome metals with CDW instabilities, and suggest a unique interplay between phonon and electron dynamics in this compound.

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M. V. Gonçalves-Faria, A. Pashkin, Q. Wang, H. C. Lei, S. Winnerl, A. A. Tsirlin, M. Helm, E. Uykur. 2023-07-11. Coherent phonon and unconventional carriers in the magnetic kagome metal Fe$_3$Sn$_2$. https://doi.org/10.1038/s41535-024-00642-6

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