Spin and spin current dynamics in low-dimensional quantum magnets, manipulation of spin and current-carrying states in quantum dots

低维关联电子系统允许新的自旋动力学和输运现象。在这个项目中，我们使用数值和分析工具，即含时密度矩阵重整化群、量子蒙特卡罗、精确对角化和微扰理论，分析了从完全定域的一维量子磁体到关联量子点的模型系统的自旋输运和动力学。在前者中，可以实现没有载流子动力学的纯磁性输运，而有限的库仑关联允许受控地跨越到后者中的定域电子的极限。考虑到平衡和非平衡两种情况，我们将研究时间和真实空间以及动量和频率分辨的自旋和自旋流动力学。我们将提取相干和松弛的特征时间尺度，并研究它们对各种控制参数的依赖关系。这些控制参数包括本征模型性质，如交换拓扑、基态纠缠、库仑关联和维度。此外，还将研究诸如温度、磁场、偏置和初始状态等外部参数的影响。最后，对杂质和声子的散射进行了研究。这项研究还旨在更好地了解在几种低维过渡金属化合物中观察到的大自旋热输运，以及双量子点中的自旋动力学，例如，石墨烯和碳纳米管中实现的双量子点。

Low-dimensional correlated electronic systems allow for novel spin dynamics and transport phenomena. In this project we use numerical as well as analytical tools, namely time-dependent density matrix renormalization group, quantum Monte-Carlo, exact diagonalization, and perturbation theory, to analyze spin transport and dynamics in model systems ranging from fully localized one-dimensional quantum magnets to correlated quantum dots. In the former, purely magnetic transport without carrier dynamics can be realized, while finite Coulomb correlations allow for a controlled crossover to the limit of localized electrons in the latter. Considering both, equilibrium as well as out-of-equilibrium situations, we will study time- and real-space as well as momentum- and frequency-resolved spin and spin current dynamics. We will extract characteristic time scales for coherence and relaxation and study their dependence on various control parameters. These control parameters include intrinsic model properties such as exchange topology, ground-state entanglement, Coulomb correlations, and dimensionality. Moreover, the impact of external parameters such as temperature, magnetic fields, bias, and initial states will be investigated. Finally, scattering off impurities and phonons will be studied. This research also aims at a better understanding of the large spin-heat transport observed in several low-dimensional transition metal compounds as well as the spin dynamics in double quantum dots, which are, for instance, realized in graphene and carbon nano-tubes.