Finite-size and nonlinear effects on the ultrafast electron transport in thin metal films

Self-consistent simulations of the electron dynamics and transport in thin metal films are performed using a semiclassical Vlasov-Poisson model. The Vlasov equation is solved using an accurate Eulerian scheme that preserves the fermionic character of the electron distribution. Although the thermodynamical properties of the ground state are accurately described by the bulk theory, the dynamical properties are strongly influenced by the finite size of the system and the presence of surfaces. Our results show that (i) heat transport is ballistic and occurs at a velocity close to the Fermi speed; (ii) after the excitation energy has been absorbed by the film, slow nonlinear oscillations appear, with a period proportional to the film thickness, which are attributed to nonequilibrium electrons bouncing back and forth on the film surfaces; (iii) except for trivial scaling factors, the above transport properties are insensitive to the excitation energy and the initial electron temperature. Finally, the coupling to the ion dynamics and the impact of electron-electron collisions are also investigated.