Image courtesy of Peter Beaucage

Image of a bismuth-based superconductor

February 9, 2016

Cornell Researchers Explain Creation of First Self-Assembling Superconductor

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An interdisciplinary team of Cornell researchers in engineering, physics and chemistry recently created the first self-assembling superconductor. The news of this development came when Science Advances published the group’s research, describing their creation of the three-dimensional gyroidal superconducting structure.

The group, led by Spencer T. Olin Professor of Engineering, Ulrich Wiesner, engaged the expertise of several Cornell faculty and researchers — including Prof. Sol Gruner and Prof. James Sethna, physics, Prof. Francis DiSalvo, chemistry and chemical biology,  Bruce van Dover, chair of the materials science and engineering department  and graduate students Spencer Robbins and Peter Beaucage. All are co-authors to the study.

“We had the perfect storm of collaborators,” Beaucage said.

The integrative approach to the research was particularly important in the study of this electronic material because it implements the self-assembling nature of organic block copolymers in the traditionally inorganic realm of superconductor nanostructures.

Speaking about the interdisciplinary essential collaborative nature of this development, Wiesner said that “it stimulates the imagination because it brings two areas together that typically don’t overlap.”

“For me it’s so fulfilling because I’ve been thinking about it for such a long time, almost 20 years,” Wiesner said. “The feedback’s been really, really good because it’s a little out of the box.”

Superconductors regularly attract  great interest and research due to their vast potential as near self-sufficient non-dissipative conduction media. These materials allow for the conduction of electrons with very little to no resistance and thus no dissipation of energy lost to heat. Superconducting wires in a magnetic field can dismiss the need for a constant current supply and their technology is used in Magnetic Resonance Imaging (MRI) scanners and fusion reactors.

Computer simulation of gyroid structure observed in superconducting materials

Image courtesy of Peter Beaucage

Computer simulation of gyroid structure observed in superconducting materials

The main drawback to superconductor technology is the necessity of operating at very low temperatures and until recently, superconducting was impossible at temperatures much higher than absolute zero. Thus, a large portion of superconductor research focuses on varying the nanostructuring and materials involved to explore the potential for improved macroscale conducting properties.

“We want to understand the materials and their properties better as we give them different structures … What happens when you start to nanostructure these materials on periodic lattices?” Wiesner said.

Wiesner first considered this idea of organic materials in three-dimensional gyroidal structures almost two decades ago, before he began working at Cornell in 1999. The porous gyroidal structure is understood as a complex cubic formation of spirals of superconducting material with 10nm sized pores dispersed throughout. Gruner advanced the concept to the use of gyroidal structures in superconductors but the team encountered a challenge in figuring out how to synthesize the structure.

After unsuccessful experimentation with other superconducting materials, Wiesner consulted Sethna as to what material could exhibit superconducting properties in this structure. Sethna, who was writing a paper on superconductors at the time, recommended Niobium Nitride, an inorganic compound that Wiesner’s group was coincidentally working with.

The process involved the use of a three-monomer chain in a triblock copolymer to form the alternating gyroidal network from direct sol-gel Niobium Oxide. While ammonia flowed over the oxide to convert it to Niobium Nitride, the sample was heated in air at 450 degrees Celsius. This heating step removed one of the two solvent-induced self-assembled gyroidal networks by evaporation.

Computer simulation of gyroid structure observed in superconducting materials

Image courtesy of Peter Beaucage

Computer simulation of gyroid structure observed in superconducting materials

“You can think of it like oil and water: you take chemistries that don’t mix,” Beaucage said. “[This] allows additives like nanoparticles to mix with only one of the block polymers.”

The subsequent heat treatment required more experimentation to find a balance between preserving structure by reducing processing temperatures and improving material properties by raising processing temperatures. When Robbins first heated the sample to 700 degrees then cooled to room temperature it did not exhibit superconducting properties. He then heated the same sample to 850 degrees in a second wash. Upon cooling, this sample showed superconducting properties. When heating the sample directly to 850 degrees in a single nitriding step proved unsuccessful, the group concluded that the sample must be heated twice, an unexpected requirement that the group cannot explain.

The use of organic materials and polymer self-assembly in synthesis is a revolutionary advancement in superconductor structure. Block copolymer self-assembly in superconductor formation allows for precise tunability of morphology, dimensionality and feature size at the mesoscale. Professor Wiesner calls this the “bottom-up” approach to superconductor formation.

“[The] information about final structure is encoded into primary sequence of polymers,” he explained.

The research related to the creation of this superconducting structure is momentous in light of the lack of studies into the effects of mesostructure on superconductivity. The experiment’s innovative implementation of organic materials is some of the first research into the area of organic material use in superconducting and composite structures.

This advancement opens many pathways for future research and collaboration between the inorganic superconductor and organic polymer fields and their scientific communities. The group plans to investigate the superconducting properties of this structure to determine the potential for elevated superconducting temperatures, conduction under different applied magnetic field conditions, or improved superconductivity. This specific structure prompts further lines of research such as inquiry into the double-heating requirement and the potential to increase conduction at large interfacial areas by filling the pores with a second material to make a composite superconductor.

Scanning electron microscope image of gyroidal structure in superconducting materials

Image courtesy of Peter Beaucage

Scanning electron microscope image of gyroidal structure in superconducting materials

The exciting potential of this development has been well-received by scientific communities and public audiences alike.

“We’ve been working on this for such a long time and think it’s so cool, and it’s really interesting to hear everyone else say [that] it’s such a neat idea,” Beaucage said.

The researchers are excited by the public’s enthusiastic response and are receiving increasing attention from the media, other scientists and researchers looking to collaborate, and even young kids sending in questions about the discovery.