Extrinsic doping on the atomic scale: Tuning metallicity in atomic Au chains

Understanding the response of low-dimensional electronic systems to external perturbations is of great interest for fundamental science as well as future applications. Here we employ plasmon spectroscopy to study the modification of metallicity in Au-induced quantum wires on the Si(553) surface by hydrogenation. The present study shows that no direct bond formation to the Au chains is necessary for controllable modifications of metallicity. Instead, changes in band structure of the whole system by H adsorbed at the Si step edges suffice via indirect interaction, as proven by the quantitative agreement between first-principles calculations and the unoccupied band structure derived from plasmon spectroscopy. Interestingly, simple electron donation has a similar effect as hydrogen adsorption at the step edges with respect to the Au bands and the dimerization of the Au chains.