FOR 1700: Metallic Nanowires on the Atomic Scale: Electronic and Vibrational Coupling in Real World Systems

本研究单元的中心主题是在明确考虑二维和三维耦合及其控制和操纵的情况下，探索和识别具有一维属性的物理场景。选择它的原因很明显：理想一维（1D）电子系统的吸引人的特殊性质，如电导的量子化，电荷密度波（CDWs）和luttinger -液体行为，加上各种不稳定性和丰富的相关相变，在实验上只能在二维（2D）或三维（3D）相互作用的系统中观察到。除了在tb>0时稳定一维特性外，这些耦合的可控修改还允许调整和改变一维行为。通过这种方式，我们试图通过实验和理论小组之间的密切合作，对这个非常有趣的领域有更深入的了解。由生长在Si或Ge表面的Au、Pt、In或Pb自组织原子链组成的金属原子线，以及由稀土元素或过渡金属形成的硅化金属线，是我们重点研究的原型一维体系。在积累经验的基础上，我们将继续研究金属丝及其电子结构的结构和相变与电子输运、单粒子和集体激发及其动力学的关系。在这个新的资助期内，重点将放在导线之间耦合的可控变化、与底层衬底的耦合以及与3D嵌入材料的耦合上。为此，我们计划通过原子和分子的吸附、阶跃密度、阶跃取向和底物的变化来控制电荷密度、长程序和局部结构。进一步的重点将放在这些系统中意想不到的大程度的自旋有序，它的稳定性和与其他参数的耦合。此外，声子和电子动力学以及光诱导相变将发挥重要作用。实验与理论之间业已建立的密切合作关系以及对同一系统应用的各种实验方法的结合将继续和加强，以全面探索这一领域。

The central topic of this 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. It was chosen for obvious reasons: The attractive special properties of ideal one-dimensional (1D) electronic systems such as quantization of conductance, charge-density waves (CDWs), and Luttinger-liquid behav- ior, coupled with a variety of instabilities with a wealth of associated phase transitions, are experimentally only observable in systems that interact in two (2D) or three (3D) dimensions. Apart from stabilization of 1D properties at T >0, controlled modification of these couplings allows tuning and changes also of the 1D behavior. In this way we try to obtain deeper insight into this highly interesting field by close collaboration between experimental and theoretical groups. Metallic atomic wires, consisting of self-organized atomic chains of Au, Pt, In or Pb grown on Si or Ge surfaces, as well as silicide wires, formed with rare earth elements or transition metals, are prototype 1D systems, on which we concentrate. Based on the gathered experience, we will continue to correlate studies of structure and phase transi- tions in the wires and their electronic structure with electronic transport, single particle and collective excitations as well as with their dynamics. In this new funding period, a focus will be put on the controlled variation of coupling between wires, coupling to the underlying substrate and to the 3D embedding material. For this purpose, we plan to ma- nipulate charge densities, long range order and local structure by adsorption of atoms and molecules, variation of step densities, step orientations and substrates. Further emphasis will be given to the unexpected large degree of spin order in these systems, its stability and coupling to other parameters. Furthermore phonon and electron dynamics will play an important role as well as photoinduced phase transitions. The already well established close collaboration between experiment and theory as well as the combination of various experimental methods applied to identical systems will be continued and intensified in order to explore this field comprehensively.