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

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.

12 pages, 14 figures

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Cited by in corpus (2)

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