Physicists shed light on key superconductivity riddle
Date: Monday, July 21, 2008 @ 23:21:06 GMT
This scanning tunneling microscope image of a bismuth superconducting
compound shows a characteristic checkerboard pattern. The researchers
believe this pattern indicates the presence of a charge density wave.
Image / Doug Wise, Kamalesh Chatterjee and Michael Boyer, MIT
(PhysOrg.com) -- MIT physicists believe they have identified a
mysterious state of matter that has been linked to the phenomenon of
Led by Eric Hudson, associate
professor of physics, the researchers are exploring materials that
conduct electricity with no resistance at temperatures around 30
degrees Kelvin above absolute zero. Such materials could have limitless
applications if they could be made to superconduct at room temperature.
Hudson's team is focusing on
the state of matter that exists at temperatures just above the
temperature at which materials start to superconduct. This state, known
as the pseudogap, is poorly understood, but physicists have long
believed that characterizing the pseudogap is important to
In their latest work, published online on July 6 in Nature Physics, they suggest that the pseudogap is not a precursor to superconductivity, as has been theorized, but a competing state.
If that is true, it could completely change the way physicists look at superconductivity, said Hudson.
"Now, if you want to explain high-temperature superconductivity and
you believe the pseudogap is a precursor, you need to explain both. If
it turns out that it is a competing state, you can instead focus more
on superconductivity," he said.
The researchers studied several samples of a bismuth compound that
superconducts at high temperatures. Each has a different level of
doping (number of extra oxygen atoms that change the material's
electrical properties), which influences both its superconducting and
"We've studied a variety of
samples and found trends which point toward one possible identity,
which is a charge-density wave," said Hudson.
Others have suggested that the pseudogap might be a charge-density
wave, but this is the first systematic study of a "checkerboard"
pattern, which appears when the material is imaged with scanning
tunneling microscopy (STM) across a range of samples. The doping
dependency of the checkerboard pattern offers strong evidence of a
charge-density wave, Hudson said.
"If it is true that the pseudogap is a charge-density wave, that
would be a major, major outcome because people have been looking for
this for the past decade," he said.
Lead author of the paper is graduate student William Wise. Other
MIT authors are graduate students Michael Boyer and Kamalesh
Chatterjee, postdoctoral associate Yayu Wang, and former postdoctoral
associate Takeshi Kondo.
Provided by MIT