EAGER: CRYO: Thermomagnetic Refrigeration

该项目由化学、生物工程、环境和运输系统部和材料研究部联合支持。许多关键的物理现象和相只能在低于1K的超低温下观察到并发生。用于量子计算、传感和通信的未来量子设备依赖于超低温物理。因此，制冷技术的进步使得亚开尔文制冷对于继续和扩大我们对基础和应用物理学的理解至关重要。目前广泛使用的制冷技术实现亚开尔文是基于稀有氦同位素3He的使用。考虑到液氦的预计短缺和高价格，开发替代技术以实现未来可持续的量子计算、传感和通信至关重要。在潜在的解决方案中，没有活动部件的固态技术很有吸引力，因为它们不需要维护。其中一个解决方案，也是本提案的重点，是恩斯特-埃廷斯豪森制冷。除了是完全固态的，这些冰箱的设计非常简单，由一种材料制成。能斯特-埃廷斯豪森制冷是指在固体材料（通常是半金属）上施加电场和磁场时，沿着样品观察到由于加热而产生的温差。铋及其含锑合金在50K-150K温度范围内是有效的热磁材料。新发现的量子材料，即所谓的拓扑半金属，具有将制冷工作温度扩展到超低温的潜力。基于PI团队主要开发的第一性原理模块，该提案包括研究拓扑半金属的热磁特性，理论上没有拟合参数，并使用描述符和机器学习来识别用于亚开尔文制冷的新热磁材料。该提案设想了三个主要推力：(1)确定在低于1K的超低温下具有较大性能的材料，(2)在2K-100K范围内实验表征热磁特性，以及(3)构建和测试一个原理验证的冰箱原型。该提案的智力价值在于对大量新发现的材料进行系统研究，这是由于最近计算方法的进步，包括该团队最近开发的基于第一原理的代码。建立和验证一套完整的理论实验工具来评估材料的潜力，可以加快发现材料独特特性的步伐。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project is jointly supported by the Division of Chemical, Bioengineering, Environmental and Transport Systems and the Division of Materials Research.Many critical physics phenomena and phases are only observable and occur at ultra-low temperatures, below 1K. Futuristic quantum-based devices for applications in quantum computing, sensing, and communications are dependent upon ultra-low temperature physics. Advances in refrigeration technologies enabling sub-Kelvin refrigeration are therefore crucial to continue and expand our understanding of fundamental and applied physics. The current widely used refrigeration technology to achieve sub-Kelvin is based on the usage of the rare helium isotope, 3He. Given the projected shortage and the high price of liquid helium, it is crucial to develop alternative technologies enabling future sustainable quantum computing, sensing, and communications. Among potential solutions, solid-state technologies with no moving parts are attractive since they do not require maintenance. One of the solutions, which is the focus of this proposal, is the Nernst-Ettingshausen refrigeration. In addition to being fully solid-state, these refrigerators have an extremely simple design and are made out of a single material. The Nernst-Ettingshausen refrigeration refers to the observation of a developed temperature difference along the sample as a result of heat pumping when an electric field and a magnetic field are applied to a solid material, usually a semi-metal. Bismuth and its alloys with antimony are shown to be efficient thermomagnetic materials in the 50K-150K temperature range. The newly discovered quantum materials, the so-called topological semimetals, have the potential of extending the refrigeration operating temperature to ultra-low temperatures. Based on PI team's primarily developed first-principles module, this proposal includes studying the thermomagnetic properties of topological semimetals, theoretically with no fitting parameters, and using descriptors and machine learning to identify new thermomagnetic materials for sub-Kelvin refrigeration. The proposal envisions three major thrusts: (1) Identify materials with a large figure of merit at ultra-low temperatures, below 1K, (2) Experimentally characterize the thermomagnetic properties in the 2K-100K range, and (3) Build and test a proof-of-principle refrigerator prototype. The intellectual merit of the proposal is in the systematic studying of a large group of newly discovered materials, which is only possible due to recent advances in computational methods, including the team's recently developed first-principle-based code. Building and validating a complete theoretical-experimental set of tools to evaluate the potential of materials enables a fast pace in the discovery of materials' unique properties.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.