Unraveling The Mysteries Of High Temperature Superconductors

Superconductors are perfect conductors with zero resistance. They can carry currents without loss of electrical energy as waste heat.

Most materials however become superconducting only at very low temperatures, requiring expensive cooling. Northeastern University Prof. Arun Bansil and his team have discovered new clues toward unraveling how superconductivity can remain intact at higher temperatures.

Bansil’s research on high-temperature superconductors was published in the May 6 issue of the journal Science.

Why High Temperature Superconductors?
The high-temperature superconductors are special because they remain superconducting above –196 °C, which is the temperature at which liquid nitrogen boils and becomes gas.

“This greatly reduces the cost of keeping the material in the superconducting state. As a result, high temperature superconductors are finding wide-ranging applications in generating high magnetic fields needed for MRI machines and maglev trains, making ultra-sensitive devices for magnetoencephalography, and as part of the electrical grid,” said Bansil.

The Path To Discovery
“Superconductivity is a magical state of matter in which electrons which normally repel each other get coaxed into dancing together as pairs,” said Bansil. “But when you heat the material, these pairs break apart and destroy superconductivity. Why these pairs remains intact for relatively high temperatures in the high temperature superconductors is a puzzle that has been baffling the scientific community for nearly quarter of a century.”

In the May 6 issue of the journal Science, Bansil’s team shows how scattering high energy x-rays from single crystals of the well-know Lanthanum-Strontium-Copper-oxide high temperature superconductor, one can directly image the character of holes doped into this material.

“Our discovery is highly significant because we now have a new tool for directly seeing what the all-important holes are doing in these mysterious materials,” Bansil said. “This provides new clues to how the material becomes superconducting and what is the ‘superglue’ that holds the electron pairs together in the material. Such understanding will be the key for us to reach the holy grail of a room temperature superconductor, which will start a new revolution in science and technology.”

Experimental teams in Japan at Spring-8 synchrotron radiation facility and Tohoku University in Sendai participated with Bansil and his team in this research.

New Applications
Bansil and his team at Northeastern have pioneered the application of high energy x-rays for unraveling the nature of electronic states in wide classes of materials.
Inspired by the present study, they are now looking for new approaches to exploit x-rays for imaging dopants in novel materials and for in situ investigation of fuel cells and Li-battery materials under ambient conditions.

Other members of Bansil’s group working on problems of x-ray scattering include Senior Research Scientist Bernardo Barbiellini-Amidei; Peter Mijnarends, Adjunct Professor; Prof. Robert Markiewicz; Stachek Kapryzk, Adjunct Professor; Associate Research Scientist Hsin Lin and graduate students Susmita Basak, Wael Al-Sawai and Ray Wang.

Prof. Arun Bansil
Bansil is the founding director of Northeastern’s Advanced Scientific Computation Center. During his 35-year career at the University, Bansil’s research has focused on understanding how electrons behave in complex novel materials and how these electrons can be probed by modern spectroscopic techniques.

Bansil founded the ELMO Laboratory for science education at Northeastern and the PASTEL program for informal science education in collaboration with the major art and science museums of Boston. In 1997, he organized the Miracle of Superconductivity Symposium at the university at which nobel laureates Robert Schrieffer, David Lee and Philip Anderson and Paul Chu, discoverer of the 123 superconductor, entertained an audience of about one-thousand with hands on demonstrations.

Bansil is the US Editor of the international Journal of Physics and Chemistry of Solids since 1994, and he served as the program manager of the Theoretical Condensed Matter Physics Program at the United States Department of Energy from 2008 – 2010.

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