Abstract
We have prepared cross-grating gate electrodes on top of a two-dimensional electron system in ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ heterostructures, which act as grating couplers. In addition to the well-known two-dimensional plasmon modes at ${\ensuremath{\omega}}_{P}{(q}_{1})$ and ${\ensuremath{\omega}}_{P}{(2q}_{1}),$ with wave vector ${q}_{1}=2\ensuremath{\pi}/a,$ where a is the grating period, we observe an excitation at ${\ensuremath{\omega}}_{P}(\sqrt{2}{q}_{1}).$ This plasma excitation oscillates in the diagonal direction with respect to the cross-grating structure, and is formed by a superposition of the plasmons in the orthogonal lattice directions with wave vectors ${q}_{x}$ and ${q}_{y}.$
Published Version
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