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，电子的行为就像独立的台球在材料中碰撞，并在这个过程中损失能量。另一方面，在超导量子材料中，许多电子集体行动，以创造一种电流可以流动而没有能量损失的状态。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，并且可能是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，包括有序状态，也会出现。最根本的障碍是理解这些额外的相互交织的秩序对超导性是有害的还是有益的。该项目使用互补扫描隧道显微镜和光谱学，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交织秩序的作用，同时使用各种条件操纵材料，如外部场或温度。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，演示和解释与该项目相关的先进实验室技术。该项目还针对通过在加州大学戴维斯分校的物理和数学科学计划的本科生研究参与者的导师的教学模块的发展，纳入代表性不足的少数民族。技术摘要了解量子材料如何发展集体电子现象是凝聚态物理学家今天面临的最大挑战之一。解开量子材料的关键来自于理解多个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，超导性可能会与电子自组织成不寻常的模式（密度波）或进入x和y方向变得不等价的状态的阶段相互交织，对于其他正方形晶体中的电子（三阶）。本项目研究非常规超导体中相互缠绕有序的作用，重点是两个重要案例：（i）利用扫描隧道显微镜和光谱学（STM/S）和共振X射线散射技术研究Ce基115族重费米子超导体中密度波有序、磁性和超导性之间的关系;（ii）利用STM/S和单轴应变控制铁基超导体的超导有序度，研究铁基超导体的超导有序度和超有序度。通过这些活动，本研究最终目标是重费米子超导体中对密度波状态的直接可视化，以及通过铁基超导体的晶体变形对超导性进行可切换控制。最后，通过将单轴应变与STM/S相结合来研究量子有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 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.