Density response in laterally modulated two-dimensional electron systems

Abstract
We have evaluated within the random-phase approximation the density-response function of laterally modulated two-dimensional electron systems, examining both single-particle and collective behavior. By varying model parameters we can produce crossovers between different response characteristics. When the lateral period is long compared to the Fermi wavelength, the excitation spectrum evolves as the modulation strength is increased from a regime of plasmon bands with small gaps to a regime of geometrically confined plasmons. Simpler theories which ignore nonlocal effects in the response kernel can provide a qualitative picture of both these extremes but fail to describe the complicated crossover behavior between them. The simpler theories also fail completely when the lateral period becomes comparable to or smaller than the Fermi wavelength. Our fully quantum-mechanical evaluations show how in this limit the response behavior changes from that of Landau-broadened plasmons at weak modulation to that of depolarization-shifted intersubband transitions at strong modulation.