EAGER: CRYO: Refrigeration across temperature scales with electrically-tunable spin-orbit materials

在信息时代的下一阶段，量子计算和通信技术将对竞争力和安全性变得越来越重要，它们需要比室温小数百到数千倍的超低温。目前，达到这种温度的主要方法依赖于在稀释冰箱中反复混合和分离氦的两种同位素He-3和He-4。然而，一般来说，氦，特别是氦-3，是稀有的，而且越来越昂贵。这对量子技术的广泛应用提出了严峻的挑战。在材料研究部的支持下，伦斯勒理工学院的研究人员研究了一种新的方法，可以在不依赖稀有元素的情况下实现超低温。具体来说，他们利用了一类被称为Rashba材料的材料中电子自旋与电场的独特相互作用。初步的模拟表明，以特定的模式和方向开关施加在这些材料上的电压可以有效地达到低温，使这些潜在的有前途的材料与稀释冰箱竞争。除了使量子技术的广泛采用，这种达到极低温度的新方法的成功可以使广泛的低温现象，如超导体，在科学和技术上更容易实现。为了教育下一代STEM劳动力，研究人员将超低温制冷的基本理论和实验演示整合到本科和研究生课程以及高中推广计划中。这有助于向未来的科学家和工程师介绍通往量子信息时代道路上的技术挑战。在材料研究部的支持下，研究人员利用Rashba自旋轨道耦合作为材料的新平台，使新方法能够达到低至0.01 K的超低温，打破了目前对稀释冰箱所需的极其罕见的He-3同位素的依赖。他们研究了新的热力学循环，利用了电子熵对电场的依赖性，这是由于Rashba材料中自旋轨道分裂随电场强度的变化而引起的。特别是，他们研究了通过Rashba材料的绝热电气化制冷的可能性，并确定这是否可以提供足够的冷却功率，以匹配甚至超过典型的稀释冰箱。研究目标包括探索具有不同自旋轨道耦合强度的Rashba材料，合成能够在这些材料中进行电场循环的结构，并量化这些材料与制冷相关的场和温度相关的热力学参数。如果成功，这种方法可以扩展到更宽的温度范围，因为Rashba能量分裂的范围很广，潜在地开辟了在单一材料平台上从液氮冷却到毫开尔文温度的途径。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。

Non-technical summaryQuantum computing and communication technologies, which will become increasingly critical for competitiveness and security in the next phase of the information age, require ultralow temperatures that are hundreds to thousands of times smaller than room temperature. Currently the predominant approach to reach such temperatures relies on repeatedly mixing and separating two isotopes of helium, He-3 and He-4, in a dilution refrigerator. However, helium in general, and He-3 in particular, are rare and increasingly expensive. This poses a severe challenge to the widespread adoption of quantum technologies. With this high risk/high reward project, supported by the Division of Materials Research, researchers at the Rensselaer Polytechnic Institute investigate a new approach for achieving ultralow temperatures without relying on rare elements. Specifically, they leverage the unique interactions of the spin of electrons in a class of materials called Rashba materials with electric fields. Preliminary simulations show that switching a voltage applied to these materials on and off in a specific pattern and direction may allow reaching low temperatures efficiently, making these potentially promising materials to compete with dilution refrigerators. In addition to enabling the widespread adoption of quantum technologies, the success of this new approach to reach very low temperatures could make a wide range of low-temperature phenomena, such as superconductors, more scientifically and technologically accessible. To educate the next generation of STEM workforce, the researchers integrate the underlying theory and experimental demonstrations of ultralow temperature refrigeration into undergraduate and graduate curricula as well as high-school outreach programs. This helps introduce future scientists and engineers to the technological challenges on the path to the age of quantum information.Technical summaryWith support from the Division of Materials Research, the researchers leverage Rashba spin-orbit coupling in materials as a new platform for enabling new approaches to reach ultralow temperatures down to 0.01 K, breaking the current dependency on the extremely rare He-3 isotope required by dilution refrigerators. They study new thermodynamic cycles that take advantage of the dependence of the electronic entropy on electric fields, due to the change of the spin-orbit splitting with electric field strength in Rashba materials. In particular, they investigate the possibility for refrigeration by adiabatic electrification of Rashba materials and determine if this can provide sufficient cooling power that matches or even exceeds that of typical dilution refrigerators. Research objectives include exploring a wide class of Rashba materials with different spin-orbit coupling strengths, synthesize structures capable of electric field cycling in these materials and quantify the field- and temperature-dependent thermodynamic parameters of these materials relevant for refrigeration. If successful, this approach may be extensible to a wide temperature range due to the broad range of Rashba energy splits, potentially opening up a pathway to cool from liquid nitrogen to millikelvin temperatures in a single material platform.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.