High pressure may help boost superconductors

Washington, May 20 : Scientists at the Carnegie Institution's Geophysical Laboratory have for the first time shown that high pressure may help boost superconductors, which are believed to have the ability to convey more than 150 times more electricity than copper wires.

Viktor Struzhkin, a researcher attached with the study, said that the new findings open a new window on understanding and harnessing the so-called high-temperature superconductors.

In their study report, published in the journal Physical Review Letters, the researchers have revealed that the early superconductors had to be cooled to extremely low (below 20 K) temperatures.

The report also says that in the 1980s, scientists discovered high-temperature superconductors made of ceramic copper oxides, called cuprates.

It further states that the scientists behind that discovery found that at temperatures as high as about 135 K, such materials transition into superconductors.

Understanding how those materials could be manipulated to operate at even higher temperatures has been one of the most important unsolved problems in physics, adds the report.

"In cuprate superconductors the atoms are arranged in a layered structure. When the material goes into the superconducting state, changes occur in the copper-oxide planes, the electron spins behave differently, the vibrational energy is altered, the charges move differently, and more," said Struzhkin.

Alexander Goncharov, who jointly authored the present study with Struzhkin, said: "Over the years scientists have found that the transition temperature can be increased with a specific amount of 'doping,' which is the addition of charged particles-either negatively charged electrons or positively charged holes. We wanted to see the effects of high pressure on one bismuth-based high-temperature cuprate. Pressure has the added bonus that it can be applied gradually, like tuning a radio. We gradually tuned in to the superconductivity and could watch what happened over a broad range of pressures."

While conducting the current study, the researchers observed the subatomic effects on the material of pressures close to 350,000 times the atmospheric pressure at sea level (35 GPa) using a diamond anvil cell to squeeze the sample and specialized techniques, Raman spectroscopy and X-ray diffraction, to measure the changes.

"21 GPa was the magic number, or critical pressure," said Tanja Cuk, the lead author and a student at Stanford University, who carried out this work as part of her Ph.D. thesis research.

"By compressing the structure, we were able to observe changes in six different physical properties. But even more exciting, the changes were similar to those observed when the material has been doped to its optimal level. This means that the critical pressure is likely related to doping. Plus, by finding that pressure can be used instead of temperature and doping, we've found an entirely new approach to studying what's behind superconducting properties of high-Tc superconductors," she added.

Struzhkin said: "This study brings us one step closer to understanding the mechanism of high-temperature superconductivity by giving a completely new perspective of the superconducting state driven by a continuous variable-pressure. It appears that superconductivity is favoured on the borderline between insulating and metallic states. By applying these high pressures, we may be able to discover the missing clues to the mechanism of the high-temperature superconductivity and move a few steps closer to using superconductors in daily life. This could change our whole energy system."

ANI