Nematic Enhancement of Superconductivity

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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.