How One-Dimensional Are Atomic Gold Chains on a Substrate?

One-dimensional (1D) wires are inherently unstable but can be stabilized by three-dimensional (3D) interaction with their environment, resulting in two-dimensional (2D) and 3D hybridization of 1D electronic states. The relevance of these interactions, which is still under debate, is exemplified by the prototypical Si(553)–Au system investigated here. This system forms double atomic 1D chains on each mini-terrace for the high-coverage phase, whereas in the low-coverage phase every second terrace is empty. The relevance of hybridization is demonstrated by the complete breakdown of the nearly free electron gas model, as revealed from plasmon dispersion. Nevertheless, the combined approach consisting of plasmon spectroscopy and first-principles calculations allows for a consistent and almost quantitative description. It further demonstrates that plasmon spectroscopy contains important information about the excitation spectrum of an electronic system. Because the coupling of the Au wires with higher dimensions through the substrate cannot be neglected, the wires are more appropriately described as an extremely anisotropic 2D object than as purely 1D.