Spintronics Meets Density Matrix Renormalization Group: Quantum Spin-Torque-Driven Nonclassical Magnetization Reversal and Dynamical Buildup of Long-Range Entanglement
Spintronics Meets Density Matrix Renormalization Group: Quantum Spin-Torque-Driven Nonclassical Magnetization Reversal and Dynamical Buildup of Long-Range Entanglement
复制标题
DOI：
10.1103/physrevx.11.021062
复制
发表时间：
2020-02
期刊：
影响因子：
--
通讯作者：
M. Petrović;P. Mondal;A. Feiguin;P. Plecháč;Branislav K. Nikoli'c
中科院分区：
文献类型：
--
作者：
M. Petrović;P. Mondal;A. Feiguin;P. Plecháč;Branislav K. Nikoli'c
我们引入含时密度矩阵重整化群（tDMRG）来解决自旋电子学中长期存在的问题--如何通过完全量子力学处理两种自旋物种的动力学来描述导电电子的流动自旋和磁性材料中的局域自旋之间的自旋转移矩（STT）。与传统的Slonczewski-Berger STT相反，在传统的Slonczewski-Berger STT中，局域自旋被视为服从Landau-Lifshitz-吉尔伯特方程的经典矢量，并且只有当流动电子的自旋极化和局域自旋非共线时，它们的STT驱动的动力学才开始，量子STT可以在这些矢量共线但反平行时发生。使用tDMRG，我们模拟的时间演化的多体量子态的电子和本地化的自旋，其中前者被注入作为一个自旋极化电流脉冲，而后者包括一个量子海森堡铁磁金属（FM）spin 1 2 XXZ链最初在基态与自旋极化反平行的注入电子。当注入的电子的数量超过局域自旋的数量时，量子STT反转局域自旋的方向，但不从初始取向旋转。这种非经典的反转，这是不存在的LLG动力学，是惊人的不均匀的整个FM链，它可以伴随着减少与本地化的自旋相关的磁化，甚至在特定的位置为零。这是因为量子STT产生了一个高度纠缠的非平衡多体状态的所有流动和本地化的自旋，尽管从最初的非纠缠基态的平凡FM。此外，在FM边缘的局域自旋之间的互信息保持非零，即使在无限的分离作为远程纠缠的动力学建设的签名。纠缠熵随时间的增长在量子和常规之间有所区别（即，非共线）设置STT，达到更大的渐近值在前一种情况下。
We introduce time-dependent density matrix renormalization group (tDMRG) as a solution to long standing problem in spintronics—how to describe spin-transfer torque (STT) between flowing spins of conduction electrons and localized spins within a magnetic material by treating the dynamics of both spin species fully quantum-mechanically. In contrast to conventional Slonczewski-Berger STT, where the localized spins are viewed as classical vectors obeying the Landau-Lifshitz-Gilbert equation and where their STT-driven dynamics is initiated only when the spin-polarization of flowing electrons and localized spins are noncollinear, quantum STT can occur when these vectors are collinear but antiparallel. Using tDMRG, we simulate the time evolution of a many-body quantum state of electrons and localized spins, where the former are injected as a spin-polarized current pulse while the latter comprise a quantum Heisenberg ferromagnetic metallic (FM) spin1 2 XXZ chain initially in the ground state with spin-polarization antiparallel to that of injected electrons. The quantum STT reverses the direction of localized spins, but without rotation from the initial orientation, when the number of injected electrons exceeds the number of localized spins. Such nonclassical reversal, which is absent from LLG dynamics, is strikingly inhomogeneous across the FM chain and it can be accompanied by reduction of the magnetization associated with localized spins, even to zero at specific locations. This is because quantum STT generates a highly entangled nonequilibrium many-body state of all flowing and localized spins, despite starting from the initially unentangled ground state of a mundane FM. Furthermore, the mutual information between localized spins at the FM edges remains nonzero even at infinite separation as the signature of dynamical buildup of long-range entanglement. The growth-in-time of entanglement entropy differentiates between the quantum and conventional (i.e., noncollinear) setups for STT, reaching much larger asymptotic value in the former case.