Anisotropic Hybridization Dynamics in the Quasi-One-Dimensional Kondo Lattice CeCo₂Ga₈ Revealed by Ultrafast Optical Spectroscopy

We investigate the ultrafast dynamics of the quasi-one-dimensional Kondo lattice CeCo₂Ga₈ using optical pump-probe spectroscopy. Time-resolved pump-probe reflectivity measurements reveal a strong anisotropy in the photoinduced response, which is a direct consequence of the material's unique electronic structure. The temperature dependence of the relaxation dynamics provides evidence for the formation of two distinct hybridization gaps that appear at different temperatures in the heavy fermion state. A direct gap of 2Δdir ≈ 50 meV that persists up to T^ ≈ 90 K, well above the coherence temperature T^* ≈ 20 K. We attribute this higher-temperature gap to the hybridization fluctuations. An indirect gap of 2Δind ≈ 10 meV opens closer to T^*, signifying the development of long-range coherence in the heavy fermion state. Furthermore, we find that the hybridization gap can be suppressed with increasing pump fluence, indicating a delicate interplay between photoexcitation and the coherent heavy fermion state. Our results provide insights into the interplay of Kondo physics and low dimensionality in CeCo₂Ga₈, and establish ultrafast optical spectroscopy as a sensitive probe of anisotropic hybridization in heavy fermion materials.