Mode-selective coherent spin lattice coupling in Cr₂Ge₂Te₆

Cr₂Ge₂Te₆ (CGT), a rare intrinsic ferromagnetic semiconductor, exhibits exotic non-equilibrium dynamics and offers promising opportunities for ultrafast lattice manipulation in spintronic and magnetoelectric devices. Here, we employ table-top broadband attosecond transient absorption spectroscopy in the extreme ultraviolet (XUV) regime to investigate CGT’s ultrafast response to near-infrared excitation over a broad temperature range. By simultaneously resolving Te N_4,5 and Cr M_2,3 edges, we disentangle carrier-induced state filling/blocking, bandgap renormalization, and spectral broadening effects, while capturing coherent modulation of the energetic landscape near the Fermi level. Notably, two distinct A_1g phonons are observed at 3.3 THz and 4.0 THz at 300 K; however, approaching the Curie temperature, the lower-energy mode remains robust while the other mode gradually diminishes until it vanishes. Complementary density functional theory (DFT) and atomistic spin dynamics (ASD) simulations reveal that these lattice excitations originate from the motion of Te ions, which modulate the superexchange interactions between Cr magnetic moments. The contrasting behavior is attributed to symmetry-restricted magneto-elastic coupling together with temperature-dependent magnetic short-range orders. These results highlight a direct connection between lattice dynamics and spin correlations, paving the way for coherent control of lattice vibrations and design of quantum devices.