Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Coherent phonon and unconventional carriers in the magnetic kagome metal Fe3Sn2

Goncalves Faria, M. V.; Pashkin, O.; Wang, Q.; Lei, H. C.; Winnerl, S.; Tsirlin, A. A.; Helm, M.; Uykur, E.


Temperature- and fluence-dependent carrier dynamics of the magnetic Kagome metal Fe₃Sn₂ were
studied using the ultrafast optical pump-probe technique. Two carrier relaxation processes (τ₁ and
τ₂) and a laser induced coherent optical phonon were observed. By using the two-temperature model
for metals, we ascribe the shorter relaxation τ₁ (∼1 ps) to hot electrons transferring their energy
to the crystal lattice via electron-phonon scattering. τ₂ (∼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 A1g 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 (ΔR/R).
This amplitude is equivalent to charge-density-wave (CDW) systems, although no signs of such an
instability were hitherto reported in Fe₃Sn₂. Our results set an unexpected connection between
Fe₃Sn₂ and kagome metals with CDW instabilities, and suggest a unique interplay between phonon
and electron dynamics in this compound.

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