Nematic Enhancement of Superconductivity

非技术摘要：向列性是铁基超导体研究中的一个中心主题，是从液晶领域借用的一个术语，在液晶领域，它指的是旋转对称性破缺但平移对称性保持不变的相。由于关于库珀电子配对产生创纪录高转变温度背后的机制的悬而未决的问题，铜氧化物和铁镍化合物材料的高温超导继续吸引和刺激科学界。这些因素不仅要求继续研究和表征已知的向列相系统，而且还需要进行额外的、有针对性的研究工作，以发现和了解其他向列相系统及其在材料物理中的潜在应用。然而，由于缺乏展示电子向列相的材料，对电子向列性及其对超导电性的影响的理解是有限的。这些材料主要局限于某些高T_c超导体和少数其他复杂材料。在这个项目中，我们进行了一系列的实验，探索向列相响应和向列相活性材料的超导态性质，以帮助理解向列相涨落对超导电性的影响，从而阐明向列相在提高铁基和铜基高温超导体相变温度中的作用。这个项目让本科生、研究生和博士后科学家参与跨学科研究和具有科学和技术意义的领域，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与马里兰天文学和物理学促进多样性(GRADMAP)计划、量子材料基础冬季学校和NIST夏季本科生研究奖学金(SURF)计划。技术摘要：作为铜和铁基高温超导系统更大的电子相图中广泛观察到的一个阶段，电子驱动的线形已经变得越来越重要。作为许多铁和铜酸盐超导体的一般特征，了解电子向列性，特别是当它与这些特定化合物有关时，对于真正理解出现高T_c的条件是必不可少的。然而，在这些系统中，其他复杂的因素，通常是长程磁序，使得向列相的影响难以分离。这个项目研究的是BaNi2As2镍-镍镍系，这是一种新发现的无磁性的向列型增强型超导体系列。输运和热力学测量以及散射实验被用来表征电子向列相性质以及超导状态的性质，因为电子系统受到化学压力、掺杂和外加应变的调节。随着越来越多的理论工作表明，向列性实际上可能与库珀配对相互作用，了解这种相关的电子相及其与配对的关系，对于理解和推进高温超导至关重要。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。

Nontechnical abstract:Nematicity, which has been a central theme in the study of iron-based superconductors, is a term borrowed from the field of liquid crystals, where it refers to a phase with broken rotational but preserved translational symmetry. High temperature superconductivity in copper-oxide and iron-pnictide materials continues to fascinate and stimulate the scientific community due to the unanswered questions about the mechanism behind Cooper pairing of electrons to produce record-high transition temperatures. These factors demand not only continued investigation and characterization of known nematic systems but an additional, targeted research effort to uncover and understand other nematic systems and its potential applications within material physics. However, understanding electronic 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. In this project, a series of experiments probing both the nematic response and the superconducting state properties of nematically active materials are performed to help understand the influence of nematic fluctuations on superconductivity, and hence elucidate the role of nematicity in enhancing transition temperatures in both iron- and copper-based high-Tc superconductors. This project involves undergraduate, graduate 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 Fundamentals of Quantum Materials Winter School, and the NIST Summer Undergraduate Research Fellowships (SURF) Program.Technical abstract:Electronically driven nematicity has taken on an increased significance as a widely observed phase in the larger electronic phase diagrams of both copper- and iron-based high-temperature superconductor systems. As a generic feature of many iron and cuprate superconductors, understanding electronic nematicity, particularly as it relates to these specific compounds, is essential to truly understanding the conditions from which high Tc emerges. However, in these systems other complicating factors, commonly long range magnetic order, make the impacts of the nematic phase challenging to isolate. This project investigates the BaNi2As2 nickel-pnictide system, a newly discovered nematically enhanced superconductor series that is free of magnetism. Transport and thermodynamic measurements as well as scattering experiments are being employed to characterize both the electronic nematic properties as well as the nature of the superconducting state as the electronic system is tuned by chemical pressure, doping and applied strain. With a growing body of theoretical work suggesting that nematicity may in fact interact cooperatively with Cooper pairing, understanding this correlated electronic phase and how it relates to pairing is thus crucial to understanding and advancing high-Tc superconductivity.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.