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，它指的是一种旋转对称性被破坏但保持平移对称性的相。 铜氧化物和铁磷属元素化物材料的高温超导性继续吸引和刺激科学界，这是由于关于电子的库珀配对产生创纪录的高转变温度的机制的未回答的问题。这些因素不仅要求对已知的碳纳米管系统进行持续的研究和表征，而且还需要进行额外的、有针对性的研究，以发现和了解其他碳纳米管系统及其在材料物理学中的潜在应用。然而，理解电子向列性及其对超导性的影响，受到缺乏表现出电子向列相的材料的限制。这些材料主要限于某些高Tc超导体和少数其他复杂材料。在这个项目中，进行了一系列实验，探索向列性活性材料的超导响应和超导态性质，以帮助理解向列性波动对超导性的影响，从而阐明向列性在提高铁基和铜基高温超导体的转变温度中的作用。该项目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，并包括参与研究生资源推进多样性与马里兰州天文学和物理学（GRADMAP）计划，量子材料基础冬季学校，技术摘要：在铜基和铁基高温超导体系统的较大电子相图中，电子驱动向列性作为一个被广泛观察到的相，具有越来越重要的意义。作为许多铁和铜酸盐超导体的一般特征，理解电子向列性，特别是当它涉及到这些特定的化合物时，对于真正理解高Tc出现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，使得磁相位的影响难以分离。该项目研究了BaNi 2As 2镍-磷属元素化物系统，这是一种新发现的向列增强超导体系列，没有磁性。运输和热力学测量以及散射实验被用来表征电子的超导性质以及超导状态的性质，因为电子系统是由化学压力，掺杂和施加的应变调谐。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以及它与配对的关系对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，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

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.