Einstein-de Haas probes of equilibrium and nonequilibrium magnetism and superconductivity

嵌入的机械角动量是所有磁性物体所固有的。丘德诺夫斯基和特哈达将磁性固体描述为大量相互作用的量子陀螺仪。由于即使是经典陀螺仪也可能表现出违反直觉的行为，这激发了磁性的复杂性。人类对磁性的理解仍然缺乏对角动量守恒的完整解释。 1915 年，爱因斯坦和德哈斯 (EdH) 进行了一项非常困难的（也是爱因斯坦唯一的）实验来测量铁中角动量与磁矩的比率。他们首次观察到微小的附加磁扭矩，该扭矩会使指南针绕其长轴旋转。不幸的是，少量的普通指南针扭矩也悄然进入。他们的结果意外地与经典预测一致，后来被认为是不正确的。我们的小组使用 21 世纪的纳米机器重新审视基础实验，例如 EdH 进行的实验。由于设备的振荡速度比 1915 年使用的设备快 100,000 倍，我们证明了违反直觉的“EdH”扭矩与普通罗盘扭矩的比率也大了 100,000 倍。在纳米器件中，EdH 扭矩可以说是最强的！最重要的是，随着振荡频率的不断增加，EdH 扭矩不会无限制地增强。研究这种缩放如何分解将揭示关于使罗盘针转动的机械扭矩实际上如何从作用于针内微观磁矩的磁扭矩产生的全新信息。这是当代自旋力学子领域的一个焦点。我们还在测量协议中添加了信号相位、其他类似波形的波峰和波谷的移动对齐。相位产生了重要的新信息，如果爱因斯坦和德哈斯当时有这种能力的话，确实可以使他们发现他们的错误。 此外，我们还将把新的 EdH 方法应用于超导体，这是一类表现出磁悬浮等奇异行为的量子材料。超导性的 EdH 研究仅在文献中报道过 3 次，最近一次是在 1958 年。现代 EdH 实验将扩展我们对超导体如何与磁场相互作用的知识，可能有助于它们在特定应用中替代稀土永磁体。拟议的研究建立在过去资助期间取得的成就的基础上，其中包括与许多学生合作建立一个科学硬件创客空间，或者用他们的话说：“The Shack，一个用于创新、研究和自主学习的跨学科研讨会”。该小屋扩大了本科生发现实验研究并做出贡献的机会，并且是拟议工作的招聘和基础设施的有机组成部分。

Embedded mechanical angular momentum is intrinsic to all things magnetic. Chudnovsky and Tejada describe a magnetic solid as a huge number of interacting quantum gyroscopes. Since even classical gyroscopes can behave counter-intuitively, this motivates the complexity of magnetism. Humanity's understanding of magnetism still lacks a complete accounting of angular momentum conservation. In 1915, Einstein and de Haas (EdH) performed a very difficult (and Einstein's only) experiment to measure the ratio of angular momentum to magnetic moment in iron. They observed for the first time a tiny, additional magnetic torque that would make a compass needle rotate about its long axis. Unfortunately, a tiny amount of ordinary compass needle torque also crept in. Their result accidentally agreed with a classical prediction, later understood to be incorrect. Our group uses 21st-century nanomachines to revisit foundational experiments such as the one performed by EdH. With devices oscillating 100,000 times faster than those used in 1915, we demonstrated that the ratio of the counter-intuitive "EdH" torque to ordinary compass torque is also 100,000 times larger. In nanodevices, the EdH torque can be the strongest one! Best of all, the EdH torque will not gain strength without limit as oscillation frequencies continue to increase. Studying how this scaling breaks down will reveal fundamentally new information about how the mechanical torque that makes a compass needle turn actually follows from the magnetic torques acting on the microscopic magnetic moments inside the needle. This is a focus of the contemporary sub-field of spin mechanics. We also add signal phase, the shifting alignment of crests and troughs of otherwise similar waveforms, to the measurement protocol. Phase yields important new information, and indeed could have enabled Einstein and de Haas to spot their error, had the capability been available in their time. Additionally, we will apply the new EdH methods to superconductors, a class of quantum materials that displays exotic behaviour such as magnetic levitation. EdH studies of superconductivity have been reported in the literature only three times, most recently in 1958. Modern EdH experiments will extend our knowledge of how superconductors interact with magnetic field, possibly contributing to their use as replacements for rare-earth permanent magnets in select applications. The proposed research builds on accomplishments from the past grant period, which included working together with many students to establish a Science Hardware Makerspace, or in their words: "The Shack, an interdisciplinary workshop for innovation, research, and self-directed learning". The Shack expands opportunities for undergraduates to discover and contribute to experimental research, and is a fully organic part of recruiting and infrastructure for the work proposed.