Thermoelectric Effects in Superconductor-Ferromagnet Hybrids

非技术摘要：热电系统将热量转换为电力，反之亦然。它们在制冷、废热回收和温度测量中有应用。由于没有气体或液体成分，也没有移动部件，热电设备体积小，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，还没有在~ 200 K以下工作的高效热电系统。该项目的重点是热电系统的制造和测量，预计在高温下是有效的。从技术角度来看，这将使以前认为不可能的应用成为可能，例如低温设备和太空望远镜的热电冷却。该项目培养了新一代的学生在量子系统，合成，表征，低温，低噪声电子学和计算的专业知识。本科生的研究和招募代表性不足的群体是通过科罗拉多矿业学院与社区学院的桥梁计划促进。此外，正在开发模块，介绍该项目背后的科学，用于Mines对丹佛公立学校，垂直技能学院（这是万年青，CO的一所学校，为有阅读障碍的儿童）和社区的推广计划。技术摘要：热电效应，通常在超导体中可以忽略不计，预计在超导体（S）-铁磁体（F）混合体中会显着增加。虽然有很多令人兴奋的理论预测，但在这一领域几乎没有任何实验研究。此外，还没有关于维度的作用和超导性质（单线态与三线态）的实验或理论研究。这是一个巨大的错失机会，原因有几个。首先，如果在低温下的高热电优值的预测是正确的，S-F系统将是在这个温度范围内唯一有效的热电。第二，在S-F界面有迷人的物理学，包括三重态超导性，在电荷和自旋输运测量中看到。热电效应为这一物理现象提供了新的探索。第三，在超导体中，与热效应相关的降维对准粒子的影响还没有被探索。最后，由于缺少“基础”实验，S-F系统中的热效应有许多令人着迷的预测尚未实现。该项目通过使用低温、电荷、自旋和热输运测量系统地研究S-F混合电路中的热电效应来填补这一空白。结果测试了现有的理论预测，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性应用。该奖项反映了NSF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.