Non-Hermitian and topological magnonics with interacting artificial spin ices for reconfigurable microwave devices

半导体定义了我们的技术格局，使我们进入了大数据计算时代。随着设备接近它们的极限，人们为特定的应用寻找替代和节能的解决方案。磁性材料提供了一种节能的替代方案，因为它们的自然运行时间为纳秒(十亿分之一秒)，并减少了通过加热造成的能量损失。这种操作依赖于磁波的激发，这种磁波在材料中传播，可以与光子学和cmos器件连接。然而，磁子衰变很快，在微米(百万分之一米)范围内可检测到的传播限制了它们的性能。在这个方案中，引入了一类新的磁性材料，它支持受约束的磁子沿其边缘传播。这种模式的空间限制确保了单向运动和更长的传播长度。此外，所提出的由强耦合纳米磁体组成的材料是“功能性”的，因为它们的性质可以主动和非破坏性地重新配置，甚至可以切换。该项目的成功将为研制性能优越的可重构微波器件开辟一条新的途径。该项目将为处于磁学前沿的不同的研究生和本科生群体提供研究机会。外联活动将使社区参与进来，并使人们认识到科学进步及其对社会的影响。该项目将允许研究生和本科生领导开发专门为K-12学生设计的扩展演示装置，并扩大未被充分代表的群体的参与。这里提出的功能材料旨在将磁振子被操纵的磁农学领域与人造自旋冰领域相结合，在人造自旋冰领域，二维晶格展示可重构的状态。这样做，就有可能利用两种不同的物理现象来实现潜在的微波应用。“磁环自旋冰”依赖于稳定的手征磁态在磁振子能带结构中诱导拓扑。在这种情况下，边缘模式预期是拓扑保护的，因此是单向的。基于PT对称性守恒，非厄米系统将利用层间强耦合和不可避免的损耗来支持单向模。为了模拟这些功能材料，这个项目引入了一种新的分析形式，它将能够处理基于哈密顿形式的任意磁性超晶格。然后，这种形式将应用于两种不同的数值格式：特征值求解器和依赖于时间的模拟。本征值求解器将提供计算磁振子带结构的手段，这是迄今为止用其他数值方法还没有有效求解的。与时间相关的模拟是一种独特的工具，它将哈密顿形式与大规模数值模拟联系起来。通过将几何学、耦合和拓扑学相结合，该项目有望在社区中引发对更大类别的功能磁性材料的研究，包括三维几何和纳米图案材料。该项目还将通过为它们的建模和随后的实验实现提供分析和数值工具，从而实现可重新配置的基于微波磁铁的器件和类似半导体的器件的下一步。该奖项反映了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。

Semiconductors have defined the landscape of our technology, enabling an era of big-data computing. As devices approach their limits, alternative and energy-efficient solutions are sought for specific applications. Magnetic materials offer an energy-efficient alternative because of their natural operation timescales of nanoseconds (one billionth of a second) and reduced energy losses through heat. This operation relies on the excitation of magnetic waves, or “magnons”, that propagate through the material and can be interfaced with photonics and CMOS devices. However, magnons decay quickly, with detectable propagation in the micrometer (one-millionth of a meter) scale that limits their performance. In this proposal, a new class of magnetic materials supporting magnons constrained to propagate along their edges is introduced. The spatial constraint on such modes ensures both unidirectional motion and longer propagation lengths. Additionally, the proposed materials composed of strongly coupled nanosized magnets are “functional” in the sense that their properties can be actively and non-destructively reconfigured and even toggled. The success of this project will open a new pathway toward reconfigurable microwave devices with superior performance. This project will provide research opportunities for a diverse graduate and undergraduate student population at the forefront of magnetism. Outreach activities will engage the community and bring awareness to scientific advances and their impact on society. This project will allow graduate and undergraduate students to lead the development of an outreach demonstration setup specifically designed for K-12 students and to broaden the participation of underrepresented groups.The functional materials proposed here aim to combine the field of magnonics, where magnons are manipulated, and the field of artificial spin ices, where two-dimensional lattices exhibit reconfigurable states. In doing so, it will be possible to harness two distinct physical phenomena for potential microwave applications. The “magneto-toroidal spin ice” relies on a stable chiral magnetic state to induce topology in the magnon band structure. In this case, edge modes are expected to be topologically protected and, therefore, unidirectional. The non-Hermitian systems will make use of strong inter-layer coupling and the unavoidable losses to support unidirectional modes based on the conservation of PT-symmetry. To model these functional materials, this project introduces a new analytical formalism that will be able to tackle arbitrary magnetic super-lattices based on a Hamiltonian formalism. The formalism will be then applied to two distinct numerical schemes: an eigenvalue solver and a time-dependent simulation. The eigenvalue solver will provide the means to compute the magnon band structure, which has not been efficiently solved by other numerical methods to date. A time-dependent simulation is a unique tool that will bridge the Hamiltonian formalism to large-scale numerical modeling. By combining geometry, coupling, and topology, this project is expected to spark the investigation of a larger class of functional magnetic materials in the community, including three-dimensional geometries and nanoscale-patterned materials. The project will also enable the next step towards the realization of reconfigurable microwave magnon-based devices and semiconductor-like devices by providing the analytical and numerical tools for their modeling and subsequent experimental realization.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.