Two-dimensional crossover and strong coupling of plasmon excitations in arrays of one-dimensional atomic wires

Dimensional crossover is of high relevance to understanding real-world quasi-one-dimensional (1D) systems. Here we study the collective excitations, measured as plasmon dispersions in an electron energy loss experiment, in a tunable family of model systems, namely, Au chains on stepped Si(hhk) substrates, that allow variations of chain widths and interchain spacings. We indeed observe 1D-like dispersions, but with a significant influence of higher dimensions. Surprisingly, we find that it is not the interchain coupling but the width of the conduction channel, as confirmed by tunneling spectroscopy, that dominates the excitations. © 2016 American Physical Society.DFG/FOR/170