Charge Transport in Nanostructures: Current-Induced Forces and Electronic Friction

纳米结构如原子线、分子结或石墨烯纳米带中的电输运通常伴随着电子与机械自由度如局部振动模式的强耦合。对于较高的偏置电压，即，远离热平衡，这种耦合引起非保守的电流感应力和与电子摩擦有关的不寻常的耗散现象，这具有重要的后果。例如，非保守的电流感应力可以引起局部振动模式和电子摩擦的强烈激发，振动自由度由于与电子的耦合而经历的电子摩擦可以呈现负值。这些效应可能导致纳米结构的机械不稳定性。详细的分析和理解的基本机制是至关重要的纳米电子架构的进一步发展。为了实现这一目标，目前的项目，这是研究单位的一部分“减少非平衡系统的复杂性”，涉及一致和准确的理论方法的发展，研究电流诱导的非平衡纳米系统的机械运动。为此，将采取两种策略，这两种策略都采用简化描述整个复杂问题的概念：（i）分层量子主方程方法，开放量子系统的数值精确方法，以及（ii）采用广义朗之万方程的量子经典概念。将这两种互补的方法应用于金属电极之间的原子纳米线，将分析电流诱导力和电子摩擦的签名，机制和后果。此外，非保守力的出现将在半经典极限内进行研究。

Electrical transport in nanostructures such as atomic wires, molecular junctions or graphene nanoribbons is often accompanied by strong coupling of the electrons to the mechanical degrees of freedom such as local vibrational modes. For higher bias voltages, i.e., far from thermal equilibrium, this coupling gives rise to non-conservative current-induced forces and unusual dissipative phenomena related to electronic friction, which have important consequences. For example, non-conservative current-induced forces can cause strong excitation of local vibrational modes and electronic friction, which the vibrational degrees of freedom experience due to coupling to the electrons, can assume negative values. These effects may cause mechanical instabilities of the nanostructures. A detailed analysis and understanding of the underlying mechanisms is crucial for the further advancement of nanoelectronic architectures. Towards this goal, the current project, which is part of the Research Unit "Reducing complexity of nonequilibrium Systems", involves the development of consistent and accurate theoretical methods to study current-induced mechanical motion of nanosystems in nonequilibrium. To this end, two strategies will be pursued, which both employ the concept of a reduced description of the overall complex problem: (i) the hierarchical quantum master equation approach, a numerically exact method for open quantum systems, and (ii) quantum-classical concepts employing generalized Langevin equations. Applying these two complementary approaches to atomic nanowires between metal electrodes, the signatures, mechanisms and consequences of current induced forces and electronic friction will be analyzed. Furthermore, the emergence of non-conservative forces will be investigated within the semiclassical limit.