Minigaps in the Plasmon Dispersion of a Two-Dimensional Electron Gas with Spatially Modulated Charge Density

In a two-dimensional electron gas with a spatially modulated charge density we observe a splitting of the two-dimensional-plasmon dispersion. The charge-density modulation is induced in a metal-oxide-silicon capacitor with a modulated oxide thickness of submicrometer periodicity. The splitting is caused by the superlattice effect of the charge-density modulation on the collective excitation spectrum and depends strongly on the Fourier expansion coefficients of the charge-density profile.