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）中的电传输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，这种耦合会产生非保守电流诱导力和与电子摩擦相关的异常耗散现象，这具有重要的后果。例如，非保守电流诱导的力可以引起局部振动模式的强烈激发，并且由于与电子耦合而经历的振动自由度可以取负值。这些影响可能导致纳米结构的机械不稳定性。详细分析和了解其潜在机制对于进一步推进纳米电子结构至关重要。为了实现这一目标，目前的项目是“降低非平衡系统复杂性”研究单元的一部分，涉及发展一致和准确的理论方法来研究非平衡状态下纳米系统的电流诱导机械运动。为此，将采用两种策略，这两种策略都采用了对整个复杂问题的简化描述的概念：(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）采用广义朗格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，分析电流感应力和电子摩擦的特征、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.