CAREER: Determining the Role of Intertwined Orders in Superconducting Quantum Materials

简单金属中电阻的起源可以用一个模型很好地描述，在这个模型中，电子的行为就像在材料内部碰撞的独立台球，在这个过程中会损失能量。另一方面，在超导量子材料中，许多电子的集体行为创造了一种电流可以流动而不损失能量的状态。在许多情况下，这些量子材料可能具有超越我们传统知识的增强特性，并且可能成为未来清洁能源传输和其他日常技术的关键。然而，当人们试图增强超导性时，其他现象，包括有序态，也会出现。最根本的障碍是理解这些额外的缠绕序是如何对超导性有害还是有益的。该项目使用互补扫描隧道显微镜和光谱学，这是一种可视化亚纳米级电子的工具，以及共振x射线散射来研究超导量子材料中缠绕有序的作用，同时使用各种条件（如外场或温度）来操纵材料。该项目还利用在线工具更广泛地传播知识。几个在线视频模块，以本科生和研究生为特色，演示和解释与本项目相关的先进实验室技术。该项目还旨在通过为加州大学戴维斯分校物理和数学科学项目的本科生研究参与者开发教学模块，将代表性不足的少数民族纳入其中。理解量子材料如何发展集体电子现象是当今凝聚态物理学家面临的最大挑战之一。解开量子材料的关键在于理解多相是如何内在地交织在一起的，并且不能单独存在。在量子材料中，超导性可能与电子自组织成不寻常的模式（密度波）或进入x和y方向变得不等效的状态（向列顺序）的相位交织在一起。本项目研究了缠绕序在非常规超导体中的作用，重点关注两个重要案例：(i)利用扫描隧道显微镜和光谱（STM/S）和共振x射线散射技术研究ce基115重费米子超导体中密度波序、磁性和超导性之间的关系；（ii）通过集成STM/S和单轴应变来控制向列序来研究铁基超导体中的超导和向列序。通过这些活动，本研究的最终目标是直接可视化重费米子超导体中的对密度波状态，以及通过铁基超导体的晶体变形来切换控制超导性。最后，通过单轴应变与STM/S的积分来研究向列序的新方法的发展将对其他量子材料的研究产生重大影响。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 AbstractThe origin of electrical resistance in simple metals is well-described by a model in which electrons behave like independent billiard balls colliding within the material, and losing energy in the process. On the other hand, in superconducting quantum materials many electrons behave collectively to create a state where electric current can flow without energy loss. In many cases, these quantum materials may feature enhanced properties that defy our conventional knowledge, and could be key to the future of clean energy transmission and other everyday technologies. However, as one tries to enhance superconductivity, other phenomena, including ordered states, appear as well. The fundamental roadblock is to understand how these additional intertwined orders are detrimental or helpful to the superconductivity. This project uses complementary scanning tunneling microscopy and spectroscopy, a tool that visualizes the electrons in the sub-nanoscale, and resonant x-ray scattering to investigate the role of intertwined orders in superconducting quantum materials, while manipulating the materials using a variety of conditions like external field or temperature. This project also uses online tools for the broader dissemination of knowledge. Several online video modules, featuring undergraduate and graduate students, demonstrate and explain the advanced laboratory techniques related to this project. This project also targets the inclusion of underrepresented minorities through the development of teaching modules for the Mentorships for Undergraduate Research Participants in the Physical and Mathematical Sciences program at UC Davis.Technical AbstractUnderstanding how quantum materials develop collective electronic phenomena is one of the biggest challenges facing condensed matter physicists today. The key to unlocking quantum materials comes from understanding how multiple phases are intrinsically intertwined and cannot exist alone. In quantum materials, superconductivity may intertwine with phases where electrons self-organize into unusual patterns (density waves) or into states where the x and y directions become nonequivalent for electrons in an otherwise square crystal (nematic order). This project investigates the role of intertwined orders in unconventional superconductors, focusing on two important cases : (i) studies of the relationship between density-wave order, magnetism and superconductivity in the Ce-based 115 family of heavy-fermion superconductors using scanning tunneling microscopy and spectroscopy (STM/S) and resonant x-ray scattering techniques; and (ii) studies of superconducting and nematic orders in Fe-based superconductors by integrating STM/S and uniaxial strain to control the nematic order. Through these activities, this research ultimately targets the direct visualization of a pair-density-wave state in a heavy fermion superconductor and the switchable control of superconductivity by crystal deformation of Fe-based superconductors. Finally, the development of a new methodology to study nematic order via the integration of uniaxial strain to STM/S will have significant impact on the study of other quantum materials.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.