Nematic Enhancement of Superconductivity

非技术摘要：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悬而未决的问题之一，而了解这些化合物的复杂正常状态本身就成为一项重大的物理挑战，这是我们理解强关联电子系统的核心。但是，在超导附近出现所谓的电子向列相，材料中的电子表现出自发的择优取向，促使人们有必要以一般的方式更好地理解这种自由度。这个项目在一个模型系统中研究了这种关系的细节，为阐明通过向列相涨落增强超导配对的潜力和理解电子向列性在凝聚态中的作用提供了重要的下一步。技术摘要：对向列性及其对超导电性的影响的理解，受到显示出电子向列相的材料的缺乏的限制。这些材料主要限于某些高T_c超导体和少数其他复杂材料，在这些材料中，其他复杂因素，通常是长程磁序，使得向列相的影响难以分离。本程序研究了一种无磁性向列型增强型超导体，即镍-磷酸盐固溶体系列Ba1xSrxNi2As2，它已被证明具有通过化学取代高度可调的新颖的结构、电荷和电子向列序。该项目包括输运、光谱和热力学测量超导带隙与应变的关系，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之间的相互作用，以1)进一步建立向列性和超导电性之间的联系，以及2)更好地理解向列性和电荷顺序之间的关系。该计划的更广泛影响涉及跨学科研究和具有科学技术意义的领域的本科生、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，并包括参与研究生资源促进马里兰天文学和物理多样性(GRADMAP)计划。该计划还与马里兰大学的年度量子材料基础冬季学校相结合，该学校专注于培养追求量子材料研究事业的下一代科学家。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.