High-Pressure Synthesis of Missing Pnictide Superconductors

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Part 1: Non-Technical summary: Lossless transmission of power means that all electricity that goes into a material is transported without loss. If achieved, this would lead to astonishing energy savings, completely transform energy generation, and significantly improve medical imaging technology. So-called superconductors demonstrate this lossless transmission of electricity making them very important for novel technologies. Superconductors also offer the potential for fundamental scientific discovery. The mechanism by which superconductors enable this energy saving phenomenon is largely not well understood. Understanding this mechanism and creating better superconductors is essential for technological application, because currently superconductivity is largely a low-temperature phenomenon, with critical temperatures for superconductors being similar to the extremely low temperatures found on Mars or even in the coldest regions of outer space. Through this award, funded by the Solid State and Materials Chemistry as well as the Condensed Matter Physics programs in the Division of Materials Research at NSF, Freedman's research team engages in a theory-inspired search for new superconductors of a specific type, which could enable fundamental insight into the mechanism of superconductivity. Her team uses high-pressure synthesis to access new compounds that have long eluded chemists. This work enables interdisciplinary training for graduate students and postdoctoral fellows, where they benefit from the scientific intersection of solid-state chemistry, physics and geophysics. Preparing graduate students to collaborate across fields strengthens the next generation of our scientifically engaged workforce.Part 2: Technical summary: The realization of high temperature superconductivity would be a transformative advance, with implications across NSF directorates ranging from improved medical imaging to fault tolerant power transmission. Thus far, the vast majority of new superconductors have been found either by serendipity, modification of known superconducting systems, or through the investigation of theoretically unlikely candidates. In stark contrast, the targeted synthesis of new systems is underdeveloped, owing to the inherent difficulty of predicting new superconducting materials. To enable rational progress, a clear design strategy is needed, which necessitates knowing the operative superconducting mechanism in a given class of superconductors. Freedman proposes the synthesis of the notably missing subclass of Fe-Bi pnictide superconductors via high-pressure synthesis. This work is motivated by Freedman's recent discovery of the first Fe-Bi bond in the solid-state, achieved through the application of high pressure and stabilized by the formation of Bi-Bi interactions. Through this award, funded by the Solid State and Materials Chemistry as well as the Condensed Matter Physics programs in the Division of Materials Research at NSF, Freedman's team characterizes novel materials both through in situ and bulk X-ray diffraction and spectroscopic methods. Materials are physically probed via magnetometry, resistivity, and heat capacity measurements. The aggregate of these data provides insight into the mechanism of superconductivity, and possible structure-function correlations. Creating and understanding different superconductors offers promise for true discovery within this complex field. The realization of a new class of superconductors would foster collaborations across the sciences and enable a deeper understanding of superconductivity. Superconductors also have tremendous potential for societal impact, ranging from MRI instrumentation to increased power transmission through the electric grid.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.