Spin-transport and spin-coherence in quantum wires and quantum dots, carbon nanotubes and graphene, spin-orbit interaction

本项目的主题是自旋相关相互作用对量子点、一维(1D)量子线和量子自旋链输运性质的影响。该项目分为三个子部分：a)我们将研究多能级点中自旋和轨道自由度的相互作用，其中自旋-轨道相互作用(SOI)或共隧穿过程导致自旋相关的相互作用。这包括研究Dzyaloshinskii-Moriya相互作用，环结构中的自旋极化电流，近藤和RKKY关联之间的竞争，以及基于石墨烯的器件中与频率相关的铅态密度的影响。B)我们将计算在存在SOI和电子-声子耦合的情况下，在量子线中以非平衡态制备的巡回自旋的完整动力学。从自旋动力学特性中提取自旋弛豫时间和自旋退相干时间。C)我们计划用低能场论计算自旋为1的Haldane链的自旋电导率。其目的是澄清半经典和全量子场理论处理之间的差异，即自旋电导率在多大程度上具有带隙内的规则部分。这三个子课题既与本研究所的实验项目密切相关，也与理论项目密切相关。对于子项目A，我们将使用我们小组最近发展的非平衡重整化群(RG)方法，而子项目B和C将使用标准玻色化和场论技术。

Topic of this project is the influence of spin-dependent interactions on transport properties of quantum dots, one-dimensional (1d) quantum wires and quantum spin chains. The project is divided in three subparts: A) We will study the interplay of spin and orbital degrees of freedom in multi-level dots, where spin-orbit interaction (SOI) or cotunnelling processes lead to spin-dependent interactions. This includes the study of the Dzyaloshinskii-Moriya interaction, spin-polarized currents in ring structures, the competition between Kondo and RKKY correlations, and the influence of frequency-dependent lead density of states for graphene-based devices. B) We will calculate the complete dynamics of an itinerant spin prepared in a nonequilibrium state in a quantum wire in the presence of SOI and electron-phonon coupling. From the spin dynamics characteristic spin relaxation and spin decoherence times will be extracted. C) We plan to calculate the spin conductivity in a low-energy field theory of the spin-1 Haldane chain. The aim is to clarify a discrepancy between semi-classical and full quantum field theoretical treatments as to what extent the spin conductivity possesses a regular part within the gap. The three sub-projects are in close relation to the experimental projects as well as the theoretical project of this Research Unit. For sub-project A we will use nonequilibrium renormalization group (RG) methods developed recently in our groups, whereas sub-projects B and C will be performed using standard bosonization and field-theoretical techniques.