尤物视频

Synopsis

When a laser pulse strikes a thin metallic film, it excites electrons from the valence band鈥攕uch as the d-band in copper or gold鈥攊nto conduction band states, thereby creating a non-equilibrium electron distribution. Notably, this process leaves the lattice temperature unchanged. Within a few hundred femtoseconds, these non-equilibrium electrons redistribute their energy through Coulomb interactions, achieving local thermal equilibrium at an elevated electron temperature and forming a thermalized electron distribution. Subsequently, the thermalized electrons lose energy via electron-phonon interactions, transferring their excess energy to the lattice. Over longer timescales, heat diffusion dominates, gradually relaxing the system back to ambient temperature.

To calculate the photoconductivity of a photoexcited metal, it is essential to understand both the electron-phonon relaxation rate and the electron-electron relaxation rate in detail. While the electron-phonon relaxation rate can be determined using Boltzmann transport theory, our work focuses on the role of electron-electron interactions in photoconductivity. Specifically, we investigate how the electron-electron relaxation rate evolves as a function of electron temperature within the framework of the two-temperature model (TTM).

We derive the electron-electron relaxation rate using two distinct semi-classical approaches. In the first method, we calculate the equilibrium scattering rates and then derive the expression for the electron-electron relaxation rate, allowing the distribution function to remain momentum-dependent. In the second method, we present a detailed derivation from an out-of-equilibrium perspective, assuming a momentum-independent electron distribution. Here, a small perturbation is introduced into the equilibrium electron distribution function, and its temporal evolution is analyzed to determine the relaxation rate. Both approaches yield expressions for the electron-electron relaxation rates that are primarily applicable in low-temperature regimes, with excellent numerical agreement observed between them.

Finally, we employ Matthiessen鈥檚 rule to compute the photo-resistivity of gold by incorporating both the electron-phonon and electron-electron relaxation rates. We then plot the resistivity as a function of electron temperature for a fixed lattice temperature, as well as a function of lattice temperature for a fixed electron temperature. These results offer valuable insights into the interplay of relaxation mechanisms in photoexcited metals.