Time-dependent screening in a two-dimensional electron gas

Transient effects during the evolution in time of the screening process are studied for the particular case of a suddenly created charge in a two-dimensional (2D) electron gas. The response of the medium is described using linear theory and the random-phase approximation to the dielectric function. The distinctive peculiarities of the excitation spectra for a two-dimensional electron gas provide a time behaviour different from the one obtained for a three-dimensional (3D) medium. We find that, for rs=2, the transition to the steady-state regime takes place in less than 0.5 fs, without showing the long-time oscillations characteristic of the 3D system. The results are explained in terms of the different nature of the 2D and 3D plasmons.