Posted in | Quantum Physics

Researchers Create First Self-Assembled Superconductor Structure

A multidisciplinary team from Cornell have built a three-dimensional, self-assembled gyroidal superconductor based on their research of nearly over two decades.

Group leader Ulrich Wiesner, right, the Spencer T. Olin Professor of Engineering, and graduate student and co-lead author Peter Beaucage, second from right, hold models of the self-assembled gyroid superconductor the group created. Also pictured are Bruce van Dover, left, professor in the Department of Materials Science and Engineering, and Sol Gruner, the John L. Wetherill Professor of Physics. Credit:Lindsay France/University Photography

The group included researchers in chemistry, engineering and physics, and was headed by Ulrich Wiesner, the Spencer T. Olin professor of engineering.

The findings are explained in detail in a paper, published in Science Advances on January 29th, 2016.

According to Wiesner, it is the first time that a superconductor has self-assembled into a 3-D porous gyroidal structure - in this case, made of niobium nitride (NbN). The gyroid can be described as a complex cubic structure, which divides space into two interpenetrating volumes, comprising various spirals. The superconducting material and pores have a dimension of approximately 10 nm, possibly leading to the superconductor’s entirely new property profiles.

Through recent experimentation, superconducting is made possible at 94 degrees below zero, compared to previous temperatures of -459.67 degrees below zero in cases of practical applications, such as fusion reactors and magnetic resonance imaging (MRI) scanners.

There’s this effort in research to get superconducting at higher temperatures, so that you don’t have to cool anymore. That would revolutionize everything. There’s a huge impetus to get that.

Ulrich Wiesner, Spencer T. Olin Professor of Engineering, Cornell University

The electron flow in superconductors takes place without resistance and energy-sapping heat, though superconductivity can still be expensive. For instance, constant cooling is required for superconducting magnets used in MRIs using a mix of liquid helium and nitrogen.

Making a gyroidal superconductor was Wiesner’s and Sol Gruner’s (the frequent co-author) dream for nearly twenty years. The purpose was to discover how it could affect the superconducting properties. Developing a method to synthesize the material was one of the main difficulties in their course of discovery.

The use of NbN as the superconductor was the breakthrough. It was inspired by a conversation between Wiesner and another co-author, James Sethna about the possibilities of using different materials for the superconductor. It was Sethna’s opinion that the NbN would be the best option. At that time, the physicist was writing a paper on superconductors.

Using solvent evaporation induced self assembly, Wiesner’s group began using organic block copolymers to make sol-gel niobium oxide (Nb2O5) into 3D alternating gyroid networks. The group built two structures that were intertwined and later removed one by heating the structure to 450 degrees.

According to Wiesner, the team’s discovery was also based on some chance. The first attempt to achieve superconductivity which involved heating of niobium oxide to 700 degrees, had not been successful. The matter was under flowing ammonia for conversion to nitride. The same material was later reheated to 850 degrees, followed by cooling and testing processes. This resulted in obtaining superconductivity.

We tried going directly to 850, and that didn’t work, so we had to heat it to 700, cool it and then heat it to 850 and then it worked. Only then.

Ulrich Wiesner, Spencer T. Olin Professor of Engineering, Cornell University

The group were not able to give an explanation as to how the heating, cooling and reheating worked, but Wiesner stated, that “it’s something we’re continuing to research,”

Due to a lack of suitable material available for testing, there was limited previous studies on mesostructured superconductors. The research carried out by Wiesner’s team is the initial step toward increased development and research in that area.

Now that we have these periodically nanostructured and porous materials, we can start to ask questions about structure property relationships, or we can fill the pores with a second material, that may be magnetic or a semiconductor, and then study the properties of these new superconducting composites with very large interfacial areas.

Ulrich Wiesner, Spencer T. Olin Professor of Engineering, Cornell University

Wiesner stated that the team’s latest attempt in the field is groundbreaking as it brings together inorganic and organic science communities.

We are saying to the superconducting community, ‘Hey, look guys, these organic block copolymer materials can help you generate completely new superconducting structures and composite materials, which may have completely novel properties and transition temperatures. This is worth looking into.’

Ulrich Wiesner, Spencer T. Olin Professor of Engineering, Cornell University

Wiesner’s paper on laser heating-induced structures from block copolymer directed self-assembly was published in Science. He pointed out that his team's work illustrates the collaborative nature of a lot of research going on at Cornell. He said that professors, grad students and students are identified more by their field of study and not by departments.

“There is a lot of interaction among these different departments, facilitated by the field structure at Cornell. At most places, they are siloed, where at Cornell, even the administrative setup is already encouraging and facilitating interdisciplinary research.”

Ulrich Wiesner, Spencer T. Olin Professor of Engineering, Cornell University

Co-lead authors on the paper, titled “Block copolymer self-assembly directed synthesis of mesoporous gyroidal superconductors,” were Spencer Robbins and Peter Beaucage, graduate students in the fields of chemistry and chemical biology, and materials science and engineering, respectively. Robbins, who graduated in January 2015, is now a materials scientist at San Francisco-based TeraPore Technologies, a startup company out of the Wiesner group.

Other team members included Francis DiSalvo, the John A. Newman Professor of Chemistry and Chemical Biology; Gruner, the John L. Wetherill Professor of Physics; and Bruce van Dover, chair of the Department of Materials Science and Engineering.

The work was funded by grants from the National Science Foundation and the U.S. Department of Energy, and it made use of the Cornell High Energy Synchrotron Source, the Cornell Center for Materials Research Shared Facility, the Kavli Institute at Cornell for Nanoscale Science, and the Cornell NanoScale Science and Technology Facility.

Source: http://www.news.cornell.edu/

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