Quasiparticle Relaxation Dynamics in Heavy Fermion Compounds

We present the first femtosecond studies of electron-phonon ([Formula presented]-ph) thermalization in heavy-fermion compounds. The [Formula presented]-ph thermalization time [Formula presented] increases below the Kondo temperature by more than 2 orders of magnitude as [Formula presented] is approached. Analysis using the two-temperature model and numerical simulations based on Boltzmanns equations suggest that this anomalous slowing down of the [Formula presented]-ph thermalization derives from the large electronic specific heat and the suppression of scattering between heavy electrons and phonons.