UT Physicists Take Major Step in Superconductivity Research

 

KNOXVILLE –- University of Tennessee and Oak Ridge National Laboratory physicists in collaboration with scientists from the National Institute of Science and Technology (NIST) and the University of Maryland have answered a key question about what high-temperature superconductors have in common.

High-temperature superconductors –- materials that conduct electricity with incredibly high efficiency at higher-than-normal temperatures — have applications in fields from medical imaging to power transmission. In the long term, superconductors could potentially help solve the world’s significant energy issues.

The UT research is published in this week’s issue of the journal Nature, one of the world’s top scientific journals.

Scientists have struggled to understand superconductivity since the early part of the 20th century. While they knew that some metals were able to conduct electricity with incredible efficiency, it only occurred at temperatures too cold to be useful. It was only 20 years ago when researchers discovered materials –- copper oxides — that had superconductivity at temperatures exceeding the liquid nitrogen boiling point (-319 F).

But science still does not understand why.

The UT research, led by associate professor of physics and astronomy Pengcheng Dai, shows that a type of electron spin motion known as magnetic resonance is common across different classes of copper oxides. This represents a significant step towards understanding these potentially useful materials.

“This work tells us that resonance must play a role of some kind in superconductivity,” said Dai, a UT-ORNL joint faculty member. “Knowing this common trait will move the research forward significantly.”

The research indicates that the resonance energy in a material is proportional to the temperature at which a metal is superconductive.

“The higher the temperature at which a material is superconducting, the more possible applications it has,” said UT physics graduate student Stephen Wilson, the paper’s lead author.

The superconducting material they used in their experiment, known as PLCCO, is a crystal grown in the laboratory at UT. Dai and Wilson both point to the fact that in the past, the crystal would have been from Japan through collaborative programs, but that UT’s campus now has the capacity to grow these crystals.

The experiments for this research were carried out at the High Flux Isotope Reactor, Oak Ridge National Laboratory and the NIST Center for Neutron Research (NCNR).

The next step in this research is to try to understand whether the common trait of resonance is the cause of, or just caused by, the superconductivity -– in essence a “chicken or an egg” dilemma, according to Dai and Wilson.

The researchers pointed to the new Spallation Neutron Source (SNS) at Oak Ridge National Laboratory and continued collaboration with NCNR as critical to continuing their work.
“The SNS will have a real impact,” said Dai. “It takes research that would have been impossible and makes it possible.”

Between the ability to grow the crystals in the lab and analyze them at SNS, in the future, their entire research could be completed in East Tennessee.

NCNR, located in Maryland, is a leading national user facility for neutron research, used by more than 2,000 scientists annually.

Joining Wilson and Dai as authors of the paper are UT postdoctoral research fellow Shiliang Li and graduate student Songxue Chi, along with H.J. Kang and J.W. Lynn of NIST. NIST, the Department of Energy and the National Science Foundation funded the research.


Contacts:

Jay Mayfield, UT Media Relations (865-974-9409, jay.mayfield@tennessee.edu)

Mark Bello, NIST Public Affairs (301-975-3776, mark.bello@nist.gov)

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