Spin and charge currents through contacted quantum spin chains: A time-dependent density matrix renormalization group study

反铁磁金属和绝缘体具有优异的性能、高灵敏度、低能耗和易于操作等优点，是新型自旋电子器件中信息编码、传输和处理的理想材料。在这样的系统中，信号的传输是由自旋电流（代表自旋角动量的流动）介导的，而不是电荷电流。为了使自旋电流进出有源反铁磁元件，（逆）自旋霍尔效应可以在电写入、读取和开关过程中被利用。在拟议的研究项目范围内，我们通过（各向异性）量子自旋（1/2或1）链在外部磁场中建立这样一个通用自旋电子装置，夹在两个二维或三维引线（储层）之间，具有强拉什巴或德雷斯豪斯型自旋-轨道耦合，并特别计算了通过该装置的自旋和电荷电流。为此，我们将基本无偏数值技术、时变密度矩阵重整化群方法（基于矩阵积状态的公式）与块Lanczos递归或树张量网络方案相结合。该算法将被并行化并在大规模计算集群上实现。在我们的理论方法中，自旋链项促进了（更标准的）铁磁和反铁磁情况，预计分别表现出扩散和弹道输运行为。此外，根据自旋-自旋相互作用的各向异性，驱动自旋链可以实现无间隙或有间隙状态，具有明显不同的输运性质。后一种情况下，增加磁场强度，自旋激发间隙减小并最终闭合，这为自旋电流的调谐/控制提供了一种手段。在超越迄今为止存在的（而不是现象学的）自旋波电流描述的过程中，我们能够分析和量化反铁磁系统自旋电子学中的固有量子效应。我们还设想通过耦合到拓扑绝缘体的量子自旋链研究自旋相关输运。

Antiferromagnetic metals and insulators are promising candidates for encoding, transferring and processing information in novel spintronic devices, which combine excellent performance, high sensitivity, low energy consumption and easy handling. In such systems the transmission of signals is rather mediated by spin currents, representing a flow of spin angular momentum, than by charge currents. To get spin currents into and out of the active antiferromagnetic component, the (inverse) spin Hall effect can be exploited in the electrical writing, reading, and switching processes. Within the scope of the proposed research project, we model such a generic spintronic setup by an (anisotropic) quantum spin (1/2 or 1) chain in an external magnetic field, sandwiched between two two- or three-dimensional leads (reservoirs) with strong Rashba- or Dresselhaus-type spin-orbit coupling at play, and calculate, in particular, the spin and charge currents through the device. To this end, we combine basically unbiased numerical techniques, the time-dependent density-matrix renormalization group method (in a matrix-product-state based formulation) with the block Lanczos recursion or tree tensor network schemes. The algorithm will be parallelized and implemented on large-scale compute clusters. In our theoretical approach, the spin-chain term facilitates both (more standard) ferromagnetic and antiferromagnetic situations, expected to show diffusive and ballistic transport behavior, respectively. Furthermore, depending on the anisotropy of the spin-spin interaction, a gapless or gapful state is realized by the driven spin chain, with notably different transport properties. Increasing the magnetic field strength in the latter case, the spin excitation gap will be reduced and finally closed, which provides one mean for tuning/control the spin current. In going beyond the hitherto existing (rather phenomenological) descriptions of spin-wave currents we are in the position to analyze and quantify intrinsic quantum effects in the spintronics of antiferromagnetic systems. We also envisage the investigation of spin-dependent transport through quantum spin-chains coupled to topological insulators.