  We have studied the photoexcited carrier relaxation dynamics in the Kondo
insulator SmB6 and the heavy fermion metal YbAgCu4 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.
