Opposing phenomena possible key to high-efficiency electricity delivery

Dec 19, 2013
Princeton University-led researchers report that the coexistence of two opposing phenomena might explain how materials known as high-temperature superconductors, which are heralded as the future of powering our homes and communities, actually work. The researchers found that electrons in copper oxide high-temperature superconductors — a copper-oxygen compound prized for making power lines because of its ability to conduct electricity with no resistance — can organize into a fixed pattern known as a charge-order state, or, at a low enough temperature, move freely as superconducting pairs to carry electricity without resistance. The researchers uniquely combined atomic-scale microscopy (front image) and a new sensitive X-ray scattering technique (rear image) to visualize the structure of the charge-order state in copper oxide and its relationship with superconductivity. The image shows that the two techniques reveal unique yet complementary images of the same charge-order state, thereby demonstrating its existence in copper oxide. The junction where the charge-order and superconducting states coexist could help scientists further develop and control superconductivity. Credit: Ali Yazdani, Department of Physics

The coexistence of two opposing phenomena might be the secret to understanding the enduring mystery in physics of how materials heralded as the future of powering our homes and communities actually work, according to Princeton University-led research. Such insight could help spur the further development of high-efficiency electric-power delivery.

Published in the journal Science, the findings provide a substantial clue for unraveling the inner workings of high-temperature superconductors (HTS) based on compounds containing copper and oxygen, or copper oxides. Copper-oxide high-temperature superconductors are prized as a material for making power lines because of their ability to conduct electricity with no resistance. It's been shown that the material can be used to deliver electrical power like ordinary transmission lines, but with no loss of energy. In addition, typical superconductors need extremely low temperatures of roughly -243 degrees Celsius (-405 degrees Fahrenheit) to exhibit this 100-percent efficiency. A copper oxide HTS, however, can reach this level of efficiency at a comparatively toasty -135 degrees Celsius (-211 degrees Fahrenheit), which is achievable using liquid nitrogen.

Copper oxides are the linchpin of the world's first superconducting electrical line, the 600-meter (1,970-foot) cable installed on Long Island in 2008 as the Holbrook Superconductor Project funded by the U.S. Department of Energy. The cable is chilled with about 49,000 liters (13,000 gallons) of liquid nitrogen. Another 3 million meters (1,860 miles) of superconducting cables are bound for a power grid in South Korea.

Despite the promise and burgeoning commercial embrace of HTS materials, scientists still do not fully understand many of the properties of these compounds, including how superconductivity occurs at such high temperatures, said Ali Yazdani, a Princeton physics professor and the Science paper's senior author. That knowledge gap has hindered the development of additional HTC materials as well as efforts to increase further the temperature at which superconductivity can occur, Yazdani said.

The secret to high-temperature superconductivity may lie at the junction of that state and its near opposite, Yazdani and his colleagues found. The researchers report that high-temperature superconductivity in copper oxides forms as the material is cooled from a state in which electrons exhibit what is normally considered a competing behavior called "charge ordering." In a superconductor, electrons overcome their repulsion and form pairs that move in unison and conduct electricity without resistance. In a charge-ordered state, interaction between electrons keeps them locked into a rigid pattern, which usually limits their ability to make the freely moving pairs required for superconductivity.

"Charge ordering is when every electron knows its place and stays there—in a superconductor, they know their place but they move in unison," Yazdani said. "It's almost like they freeze into this patterned charge-order state, and just before they become stuck they change their minds and do exactly the opposite."

The researchers' finding provides an important indication about the point at which a material potentially becomes an HTS, Yazdani said. From there, scientists may one day figure out how to enhance superconductivity, possibly even determining how it can occur at higher temperatures, he said.

There has been a previous indication of the interplay between the charge-order and superconducting states. Yazdani and his co-authors, however, combined atomic-scale microscopy and a new sensitive X-ray scattering technique to demonstrate that this phenomenon is ubiquitous across different families of copper-oxide superconductors. Their approach also presented a new method for visualizing the structure of a charge-order state and for more precisely identifying the state's relationship with superconductivity.

"Understanding and improving the properties of these materials is one of the grand challenges of our field," Yazdani said. "To make a charge-order state you use the same ingredients as a superconductor but at some point the electrons bifurcate into a state you want and the one you don't. In order to understand the one you want, you need to understand where they both came from."

Yazdani worked with co-first authors Eduardo da Silva Neto, who received his doctorate from Princeton and is now a postdoctoral researcher at the University of British Columbia, and Princeton postdoctoral researcher Pegor Aynajian, who recently became a physics professor at Binghamton University. Also involved were Princeton graduate student András Gyenis and researchers from Brookhaven National Laboratory, the Max Planck Institute for Solid State Research in Stuttgart, Germany, the Helmholtz-Zentrum Institute for Materials and Energy in Berlin, the University of British Columbia, and the Central Research Institute of Electric Power Industry in Tokyo.

Explore further: X-rays reveal another feature of high-temperature superconductivity

More information: "Ubiquitous Interplay between Charge Ordering and High-Temperature Superconductivity in Cuprates" Science, 2013.

Related Stories

Recommended for you

Quantum mechanics to charge your laptop?

2 hours ago

Top scientists from UC Berkeley and MIT found the expertise they lacked at FIU. They invited Sakhrat Khizroev, a professor with appointments in both medicine and engineering, to help them conduct research ...

Magnetic neural control with nanoparticles

3 hours ago

Magnetic nanoparticles don't have to be "one size fits all." Instead, individual magnetic nanoparticles can be tailored in an array of differing sizes and compositions to allow for heating them separately ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

orti
not rated yet Dec 19, 2013
It's amazing that the state of organization of moving electrons can be viewed at all, let alone inside of a "solid" conductor.
thingumbobesquire
not rated yet Dec 20, 2013
Here, as always, nonlinear phase changes characterize living, inorganic, noetic realms and their interactions. They are a species of potential inherent in the composition of the universe. They can result in catastrophe or progress. The human alone, at least that we know of, has the freedom to discover this self similarity of potential development and harness it.
Macksb
not rated yet Dec 20, 2013
Think of Runner A on oval running track A, and Runner B on oval running track B. The two tracks do not touch each other. That is the undesirable state. Then imagine that tracks A and B are contiguous at some point, or overlap. In that case, Runner A and Runner B become paired, as Cooper pairs, antisynchronously. B must be 180 degrees out of phase with A, exactly. Notionally, the two tracks become one.

This is a simple case of Art Winfree's law of coupled oscillators.

I suggest that Tracks A and B overlap as an indirect consequence of the uniquely large amplitude described in a recent Physorg article (November 24): "X rays reveal another feature..." The overlap may be temporary but at regular intervals. This would force Runners A and B (two electrons) to coordinate their positions.

The Nov. 24 article also cites a very narrow region of phonon wavelengths and a very low energy of atomic vibration. Both imply highly coordinated lattice vibrations.