Computational design of magnon spintronic devices with multiscale approach by combining time-dependent quantum transport with classical micromagnetics

传统的自旋电子学使用电子的自旋电流来携带、传输和处理信息。然而，它们在短距离内衰变的同时也会产生焦耳热损失。冲击在磁性绝缘体上的电子自旋电流被转换为由定域磁矩的集体运动携带的自旋电流。由于电子不会通过绝缘体，因此这种自旋波或磁振子自旋电流可以在很长的距离内传播，而不会产生焦耳热损失。当自旋电流在具有易平面各向异性的室温磁绝缘体内通过进动磁矩的螺旋结构传输时，自旋电流的空间衰减甚至更慢，分享了许多在低温下无耗散的相干和超流体传输的特征。此外，自旋波可以干扰并表现出非线性波相互作用，这可以用于新型基于波的逻辑门，以及在同一芯片上混合逻辑和存储器，以避开传统电子学中远距离慢速存储器和快速逻辑门之间数据交换的瓶颈--所谓的存储器墙。超流自旋输运可以被用来创造超导约瑟夫森结的磁性类似物。这项研究将使用最新开发的计算工具来模拟电子自旋电流和自旋波或超流体自旋电流之间的相互转换，从而为器件制造提供精确的指导，通过对跨磁绝缘体的长距离和低耗散自旋编码信息流的优化控制，以及对正常金属接触的体相或近界面的探测来提供精确的指导。拟议研究的更广泛影响将包括：为超低功耗的新型计算技术设计积木；为研究生提供高级量子设备建模和超级计算模拟方面的培训；以及创建新的公开可用的设备建模软件。磁振子自旋电子器件的可扩展性需要有效的方案来激发短波长的交换自旋波，这将通过模拟由两个磁畴壁或单个电流驱动的域壁产生的纳米波长的自旋波来进行研究。这些设置也将是模拟内存中逻辑设备的基础，在这种设备中，域壁存储二进制信息，而自旋波通过遍历它们来执行逻辑操作。我们将模拟在具有易轴各向异性的铁磁和反铁磁绝缘体上调制自旋波自旋电流的磁农阀和晶体管。我们将研究通过易平面各向异性的磁性绝缘体调制超流体自旋电流的方案，包括约瑟夫森结的磁性类似物。在所有这些设备中，读出由磁性绝缘体处理的信息需要最终将由局域磁矩动态携带的自旋电流转换为传统的电子自旋和电荷电流。整个过程将通过利用并进一步发展最近发展的多尺度框架的理论和计算能力来微观模拟，该框架自洽地将电子的含时非平衡格林函数算法与用于局域磁矩经典动力学的Landau-Lifshitz-Gilbert方程相结合。这一框架使得首次能够以时间分辨的方式直接研究注入电子自旋电流(稳定的或脉冲的)如何通过自旋扭矩激发自旋波或超流体自旋输运，以及它们如何通过自旋泵浦效应激发电子自旋电流。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Conventional spintronics employs spin currents of electrons to carry, transport and process information. However, they decay over short distances while also generating Joule heat losses. Electronic spin current impinging onto a magnetic insulator is converted into spin current carried by collective motion of localized magnetic moments. Such spin wave or magnon spin currents can propagate over long distances without Joule heat losses since electrons do not move through an insulator. Even slower spatial decay of spin currents becomes possible when they are transported by spiraling textures of precessing magnetic moments within room temperature magnetic insulators with easy-plane anisotropy, sharing many features of coherent and superfluid transport without dissipation at cryogenic temperatures. In addition, the spin waves can interfere and exhibit nonlinear wave interaction which can be exploited for novel wave-based logic gates, as well as for mixing of logic and memory on the same chip to evade the so-called memory wall as a bottleneck in data exchange between distant slow memory and fast logic gates in conventional electronics. The superfluid spin transport can be exploited to create magnetic analogues of superconducting Josephson junctions. The proposed research will employ newly developed computational tools to simulate interconversion between electronic spin currents and spin wave or superfluid spin currents, thereby offering a precise guidance for device fabrication with optimal control of long-distance and low-dissipation spin-encoded information flow across magnetic insulators and its probing in the bulk or near interfaces with normal metals contacts. Broader impact of the proposed research will include: design of building blocks for novel computing technologies with ultralow power consumption; training for graduate students in advanced quantum device modeling and supercomputing simulations; and creation of new publicly available device modeling software.The scalability of magnon spintronic devices requires efficient schemes to excite exchange spin waves of short wavelength, which will be investigated by simulating spin waves of nanoscale wavelength generated by annihilation of two magnetic domain walls or by a single current-driven domain wall. These setups will also underlie simulations of logic-in-memory devices where domain walls store binary information while spin waves perform logic operations by traversing them. Magnon valves and transistors which modulate spin wave spin current across ferro- and antiferromagnetic insulators with easy-axis anisotropy will be simulated. Schemes to modulate superfluid spin currents across magnetic insulators with easy-plane anisotropy will be investigated, including magnetic analogues of Josephson junctions. In all of these devices, readout of information processed by magnetic insulator requires to eventually convert spin currents carried by the dynamics of localized magnetic moments into conventional electronic spin and charge currents. The whole process will be modeled microscopically by utilizing and further advancing theoretical and computational capabilities of recently developed multiscale framework which self-consistently combines time-dependent nonequilibrium Green function algorithms for electrons with the Landau-Lifshitz-Gilbert equation for classical dynamics of localized magnetic moments. This framework makes it possible for the first time to directly, and in time-resolved fashion, investigate how injection of electronic spin current (steady or pulsed) excites spin waves or superfluid spin transport by spin torque and, how they excite electronic spin currents via the spin pumping effect.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.