Fingerprints of Excitonic Collective Modes in the Two-Dimensional Electron Gas
The study investigates collective charge excitations in a two-dimensional electron gas (2D HEG) at low densities using time-dependent density functional theory. It found new excitonic modes emerge beyond traditional plasmons when the Wigner-Seitz radius is large ($r_s eq 1$). These modes leave experimental fingerprints, such as asymmetric peaks in the loss function and strong oscillations in the static density response, indicating an instability towards a charge-density-wave phase.