Anomalous Hot Carrier Decay in Ferromagnetic Cr2Ge2Te6 via Spin-Phonon Coupling.

The link between spin-phonon coupling (SPC) and coherent phonon excitation as well as hot carrier decay dynamics is investigated with femtosecond transient optical spectroscopy. Coherent phonon excitation via SPC is directly observed in a van der Waals ferromagnet Cr2Ge2Te6 (CGT). Such coherent phonon excitation is strongly dependent on spin ordering of CGT and facilitates considerably hot carrier decay. While hot carriers decay normally via direct electron-phonon coupling, hot carrier decay in ferromagnetic CGT is also achieved via indirect electron-phonon coupling, with spin ordering acting as the intermediate between hot carriers and coherent phonons.