Thermoelectric Effects in Superconductor-Ferromagnet Hybrids

非技术摘要：热电系统将热能转化为电能，反之亦然。它们在制冷、废热回收和测温方面都有应用。热电装置没有气体或液体成分，也没有活动部件，体积小，便携，坚固。然而，热电材料的能量转换效率随着温度的降低而降低。因此，到目前为止，还没有有效的热电系统在~ 200k以下运行。这个项目的重点是制造和测量热电系统，预计在高温下是有效的。从技术的角度来看，这将使以前认为不可能的应用成为可能，比如低温设备和太空望远镜的热电冷却。该项目培养具有量子系统、合成、表征、低温、低噪声电子学和计算等专业知识的新一代学生。科罗拉多矿业学院与社区学院的桥梁项目促进了本科生研究和招募代表性不足的群体。此外，正在开发模块，介绍该项目背后的科学，用于Mines向丹佛公立学校，垂直技能学院（这是一所位于科罗拉多州常青的诵读困难儿童学校）和社区的推广计划。技术摘要：在超导体中通常可以忽略不计的热电效应，在超导体(S) -铁磁体(F)杂化中有望显著增加。尽管令人兴奋的理论预测比比皆是，但在这一领域几乎没有任何实验研究。此外，关于维数的作用和超导性质（单重态与三重态）的实验或理论研究都没有。由于几个原因，这是一个巨大的错失机会。首先，如果低温下高热电值的预测是正确的，那么S-F系统将是该温度范围内唯一有效的热电系统。其次，在S-F界面上有迷人的物理现象，包括在电荷和自旋输运测量中看到的三重态超导性。热电效应为这一物理学提供了一个新的探索。第三，降维对超导体中与热效应相关的准粒子的影响尚未得到探讨。最后，由于缺乏“基础”实验，对S-F系统中的热效应有许多令人着迷的预测尚未实现。这个项目通过使用低温、电荷、自旋和热输运测量系统地研究S-F混合动力车的热电效应，填补了这一空白。结果验证了现有的理论预测，为未来的研究提供了信息，并探索了包括纳米级冷却在内的预示应用。这些努力建立在PI在纳米级制造和低温输运实验方面的专业知识之上。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 abstract: Thermoelectric systems convert heat to electricity and vice versa. They have applications in refrigeration, waste heat recovery, and thermometry. With no gas or liquid components and no moving parts, thermoelectric devices are small, portable, and sturdy. However, the energy conversion efficiency of thermoelectric materials decreases with decreasing temperature. Therefore, to date, there is no efficient thermoelectric systems operating below ~ 200 K. The thermoelectric system this project is focused on fabricating and measuring, is predicted to be efficient at elevated temperatures. From a technology perspective, this will enable applications that were previously thought impossible such as thermoelectric cooling for cryogenic devices and space telescopes. This project trains a new generation of students with expertise in quantum systems, synthesis, characterization, cryogenics, low-noise electronics, and computation. Undergraduate research and recruitment of underrepresented groups is facilitated through Colorado School of Mines' bridge program with community colleges. Additionally, modules are being developed, introducing the science behind this project, for use in Mines' outreach programs to Denver Public Schools, Vertical Skills Academy (which is a school for dyslexic children in Evergreen, CO), and the community.Technical abstract: Thermoelectric effects, which are normally negligible in superconductors, are expected to increase dramatically in superconductor (S) - ferromagnet (F) hybrids. Although exciting theoretical predictions abound, there are hardly any experimental studies in this field. Moreover, there are no studies, experimental or theoretical, on the role of dimensionality and the nature of superconductivity (singlet vs. triplet). This is a tremendous missed opportunity for several reasons. First, if the predictions of high thermoelectric figure of merit at cryogenic temperatures are correct, S-F systems will be the only efficient thermoelectrics in this temperature range. Second, there is fascinating Physics at S-F interfaces, including triplet superconductivity, seen in charge and spin transport measurements. Thermoelectric effects offer a novel probe into this Physics. Third, the effects of reduced dimensionality on quasiparticles in a superconductor, which are relevant for thermal effects, has not been explored. Finally, there are a number of fascinating predictions for thermal effects in S-F systems that have not been realized because the 'groundwork' experiments are missing. This project fills this gap by systematically investigating thermoelectric effects in S-F hybrids using low-temperature, charge, spin and thermal transport measurements. The results test existing theoretical predictions, inform future studies and explore heralded applications including nanoscale cooling. These efforts build upon the PI's expertise in nanoscale fabrication and low temperature transport experiments.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.