Hybridization dynamics in CeCoIn5 revealed by ultrafast optical spectroscopy

Abstract

We investigate the quasiparticle dynamics in the prototype heavy fermion CeCoIn${}_5$ using ultrafast optical pump-probe spectroscopy. Our results indicate that this material system undergoes hybridization fluctuations before full establishment of the heavy electron coherence, as the temperature decreases from $\sim$120 K ($T^{†}$) to $\sim$55 K ($T^{\ast }$ ). We reveal that the observed anomalous phonon softening and damping reduction below $T^{\ast }$ are directly associated with opening of an indirect hybridization gap. We also discover a distinct collective mode with an energy of $\sim$8 meV, which may be the experimental evidence of the predicted unconventional density wave. Our observations provide critical informations for understanding the hybridization dynamics in heavy fermion materials.