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

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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.