Hybridization Dynamics in CeCoIn5 Revealed by Ultrafast Optical Spectroscopy

Abstract

We investigate the quasiparticle dynamics in the prototype heavy fermion CeCoIn5 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 ∼120 K (T † ) to ∼55 K (T * ). We reveal that the observed anomalous phonon softening and damping reduction below T * are directly associated with opening of an indirect hybridization gap. We also discover a distinct collective mode with an energy of ∼8 meV below 20 K, 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.

Schwinger boson approach for the dynamical mean-field theory of the Kondo lattice

“…1(b), a hybridization gap opens on the electron dispersion. It already emerges above the Kondo temperature but only becomes fully opened at lower temperatures, in agreement with the ARPES measurement on CeCoIn 5 [32,33] and the suggested two-stage process by exact determinant quantum Monte Carlo simulations [34] and the pump- probe experiment in CeCoIn 5 [35]. Correspondingly, a pseudogap structure is seen in Fig.…”

Universal behavior in the Nernst effect of heavy fermion materials

“…On the other hand, our Nernst data for CeCoIn 5 are only below 25 K. It will be interesting to see if higher-temperature data might follow the same scaling with a larger T * . In a recent pump-probe experiment on CeCoIn 5 [47], two collective modes have been detected to emerge below these two temperatures, respectively. It could be possible that there exist multiple hybridization processes, and the Nernst effect is more sensitive to the lower-temperature one.…”

Uncovering the peculiar 4f electrons in heavy fermions

“…This highlights the importance of excited crystal electric field states in the formation of heavy bands and calls for a fundamental rethinking of the lattice effect on the hybridization process. The high-temperature onset was also supported by an optical pump-probe measurement [2], which further implied that T* could be associated with the emergence of collective hybridization. For anti-ferromagnetic (AFM) CeRhIn 5 , where local-type quantum criticality was proposed (Figure 1(b)), band-dependent hybridization is observed well above T N (=3.8 K) [3], although the Fermi surface (FS) is still dominated by conduction bands.…”