We have studied the photoexcited carrier relaxation dynamics in the Kondo insulator ${\mathrm{SmB}}_6$ and the heavy fermion metal ${\mathrm{YbAgCu}}_4$ as a function of temperature and excitation level. The dynamic response is found to be both strongly temperature dependent and nonlinear. The data are analyzed with a Rothwarf-Taylor bottleneck model, where the dynamics are governed by the presence of a narrow gap in the density of states near the Fermi level. The remarkable agreement with the model suggests that carrier relaxation in a broad class of heavy electron systems (both metals and insulators) is governed by the presence of a (weakly temperature dependent) hybridization gap.

• Received 20 June 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.037401