Nonlocality in the Two-Dimensional Plasmon Dispersion

Abstract

Two-dimensional plasmons have been investigated in AlGaAs-GaAs heterostructures with transmission spectroscopy. In a magnetic field $B$, we observe an interaction of the plasmon excitation with harmonics of the cyclotron-resonance frequency ${\ensuremath{\omega}}_{c}=\frac{\mathrm{eB}}{m}$, which arises from nonlocal effects on the two-dimensional-plasmon excitation and is governed by the parameter ${(\frac{q{v}_{\mathrm{F}}}{{\ensuremath{\omega}}_{c}})}^{2}$ ($q$ is the plasmon wave vector; ${v}_{\mathrm{F}}$ is the Fermi velocity). The dispersion and the excitation strengths of the combined resonances are in excellent quantitative agreement with a quasiclassical nonlocal theory.