Nematic Enhancement of Superconductivity

摘要：铁基和铜基超导体中前所未有的高转变温度仍然是凝聚态物理学中最重要的未解决问题之一，理解这些化合物的复杂正常状态本身已经成为一个重大的物理学挑战，这是我们探索理解强相关电子系统的核心。但是，在所谓的电子向列相超导附近的出现，材料中的电子表现出自发的优先取向，推动了以一般方式更好地理解这种自由度的需要。该项目研究了模型系统中这种关系的细节，为阐明通过向列波动增强超导配对的潜力和理解电子向列在凝聚态物质中的作用提供了重要的下一步。技术摘要：对向列相及其对超导性的影响的理解，由于缺乏证明具有电子向列相的材料而受到限制。这些材料大多局限于某些高tc超导体和少数其他复杂材料，其中其他复杂因素，通常是长范围磁顺序，使向列相的影响难以隔离。本程序研究了一种无磁性的向列增强超导体，即镍镍固溶体系列Ba1 xSrxNi2As2，它已被证明具有新颖的结构，电荷和电子向列顺序，可通过化学取代进行高度调节。该项目涉及超导间隙随应变的输运、光谱和热力学测量，利用热输运和光电发射评估对称性和能带结构，以及电荷顺序和超导性之间的相互作用，以1)进一步建立向列性和超导性之间的联系，2)更好地理解向列性和电荷顺序之间的关系。该计划的广泛影响涉及跨学科研究和科学技术意义领域的本科生，研究生和博士后科学家，包括与外部机构的合作和交流计划，并包括参与马里兰天文学和物理学研究生资源推进多样性（GRADMAP）计划。该项目还与马里兰大学的年度量子材料基础冬季学校对接，该学校专注于培养下一代从事量子材料研究的科学家。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: The unprecedentedly high transition temperatures in iron- and copper-based superconductors remain as one of the most important unsolved problems in condensed matter physics, and understanding the complex normal state of these compounds has become a major physics challenge in its own right, one that sits at the core of our quest to understand strongly correlated electron systems. But the appearance in the vicinity of superconductivity of so-called electronic nematic phases, where the electrons in a material exhibit a spontaneous preferred orientation, drives the need to better understand this degree of freedom in a generic manner. This project studies the details of this relationship in a model system, providing an important next step in elucidating the potential for enhancing superconducting pairing via nematic fluctuations and understanding the role of electronic nematicity in condensed matter. Technical Abstract: Understanding nematicity, and its impact on superconductivity, is limited by the dearth of materials demonstrated to exhibit an electronic nematic phase. These materials are mostly limited to certain high-Tc superconductors and a small handful of other complex materials where other complicating factors, commonly long range magnetic order, make the impacts of the nematic phase challenging to isolate. This program investigates a nematically enhanced superconductor free of magnetism, namely the nickel-pnictide solid solution series Ba1 xSrxNi2As2, which has been shown to exhibit novel structural, charge and electronic nematic orders that are highly tunable by chemical substitution. The project involves transport, spectroscopic and thermodynamic measurements of the superconducting gap dependence on strain, evaluation of symmetries and band structure using thermal transport and photoemission, and the interaction between charge order and superconductivity to 1) further build the connection between nematicity and superconductivity, and 2) better understand the relationship between nematicity and charge order. The broader impact of this program involves undergraduate students, graduate students, and postdoctoral scientists in interdisciplinary research and areas of scientific and technological significance, including collaborative and exchange programs with external institutions, and includes participation in the Graduate Resources Advancing Diversity with Maryland Astronomy and Physics (GRADMAP) program. The program also interfaces with the University of Maryland’s annual Fundamentals of Quantum Materials Winter School, which focuses on training the next generation of scientists pursuing careers in quantum materials research.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.