Visualizing electron–phonon and anharmonic phonon–phonon coupling in the kagome ferrimagnet GdMn6Sn6

Abstract

Kagome magnet RMn6Sn6 (R = Gd-Tm, Lu) with unusual lattice geometry and breaking of time-reversal symmetry is a promising platform to investigate the interaction of topology and magnetism. Since phonons play a vital role in the coupling between magnetism and topological fermions, a fundamental understanding of phonon dynamics is of great significance in this emerging research field. Here, we report a systematic investigation of ultrafast coherent phonon dynamics in GdMn6Sn6 crystals as a function of temperature and excitation fluence using time-resolved pump-probe spectroscopy. When the temperature decreases, the coherent phonon exhibits a hardening trend in frequency with a suppressed decay rate, which can be well-explained by the anharmonic scattering model. Unexpectedly, both the frequency and decay rate of coherent phonons are almost independent of excitation fluence, suggesting a weak electron–phonon scattering process in GdMn6Sn6.