Quasi-electron and phonon interactions in the femtosecond time domain

Abstract

The properties of optically excited particles in ultra thin metallic films differ markedly between the femto, and the picosecond time domain. In the specific case of Au films, the difference arises from the lack of thermal equilibrium in the femtosecond domain. It is also observed that some quasi-particles travel essentially unhindered, i.e., ballistically at near the Fermi velocity. It is further concluded that although a large number of phonons are produced through the decay of electrons, only a small fraction of the phonon energy returns to the quasi-electrons. It is further demonstrated that the experimental results are not consistent with the so-called “two temperature model (TTM)”, and that an attempt to use classical thermal dynamics, when a system is not in thermal equilibrium, is difficult to justify. We demonstrate that excellent agreement exists between experiment and Fermi-liquid theory (FLT), and that many parameters and functional relations, which describe quasiparticle dynamics and transport, can be recovered by the application of FLT to the experimental results.