ω²(q) = (ne²/2mε₀)·q — √q acoustic plasmon vs 3D ω_p constant
In a 2D electron gas, the long-wavelength plasmon dispersion is ω ∝ √q (vs constant ω_p in 3D). This acoustic-like dispersion arises from the 2D Coulomb interaction V(q)=e²/2ε₀q. At finite q, Landau damping occurs when ω enters the electron-hole continuum above the Fermi velocity line.