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Metallic nanowires at the atomic scale:Electronic and vibrational coupling in real world systems


Ideal one-dimensional (1D) electronic systems have peculiar properties, such as quantization of conductance, charge-density waves (CDWs), and Luttingerliquid behavior, a variety of instabilities with a wealth of associated phase transitions. These are due to their reduced dimensionality and the concomitant high electronic correlations. However, systems that are experimentally realized are inevitably coupled in two (2D) or three (3D) dimensions. Thus their properties are stabilized at higher temperatures, but on the other hand, the 1D properties may be modified or even destroyed. Therefore, the central topic of this proposed Research Unit is the exploration and identification of physical scenarios with one-dimensional properties under explicit consideration of 2D and 3D coupling, their control and their manipulation. This highly interesting field is still largely unexplored both from the experimental and the theoretical side. Metallic nanowires are prototype 1D systems. We will concentrate on these systems, and will explicitly consider them on well defined Si and Ge surfaces with crosssectional widths of only a few atomic lattice constants. They will be grown by self-assembly with noble metals (Pt, Au), Pb, In and with silicides of rare earth elements and transition metals. Using both high symmetry planes and appropriate vicinal Si and Ge surfaces we will investigate systematically the intriguing question of coupling between wires, coupling to the underlying substrate and to the 3D embedding material. We plan to explore the consequences of these interactions with respect to intrinsic instabilities (e.g. formation of charge density waves) and potential functionalities. Our investigations will comprise both studies of ground state as well as of excited state properties in order to get information about electron-electron and electron-phonon coupling. Therefore, the structure and phase transitions in the wires and their electronic structure as a function of temperature and of wire density will be correlated with electronic transport, single particle and collective (plasmonic) excitations as well as with their dynamics. In order to explore this field with its great variety of physical phenomena successfully and in reasonable depth, a close collaboration between experimental and theoretical groups is envisaged as well as thecombination of various experimental methods.

(The picture shows an STM image of five atomically-resolved Au-chains on Si(553), by c. of J.Schäfer)