Nematic Enhancement of Superconductivity

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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.