Cornell physicist J.C. Séamus Davis and colleagues at Tokyo University and AIST Labs, Tsukuba, Japan, have been watching superconductors ever so closely, atom by atom in fact. Now, his shocking observations could turn up the heat on this area of research as he has found that high-temperature superconductors may be much more like low-temperature superconductors than scientists previously thought. The discovery has implications for making new superconducting materials.
Superconductors carry an electric current with almost zero resistance, but usually only at temperatures well below zero. Researchers are keen to find ways to make these technologically useful materials operate at much higher temperatures where they might reduce significantly the energy requirements of electricity generation and transmission systems. The work of Davis and colleagues at Cornell University could shed light on how superconductivity works in modified copper oxides known as cuprates, which superconduct at the relatively high temperature of liquid nitrogen.
J. C. Séamus Davis
The team used an analytical technique developed at Cornell a decade ago to measure the vibrations of a single atom, Davis extended the measurements across an entire sample, using an improved scanning tunnelling microscope (STM). The STM uses a probe with a single atom at its tip to map out the surface of their sample of bismuth strontium calcium copper oxide (the superconducting cuprate) down to the nanoscale.
The main expectation has been that electron pairing in cuprates is due to magnetic interactions. The objective of our experiment was to find the magnetic glue, Davis explains. However, instead of finding what they were looking for the researchers came theoretically unstuck. They discovered that rather than being arranged regularly the distribution of paired electrons in a common high-temperature superconductor are disordered and so too was the distribution of phonons, the vibrating structures in a crystal lattice. This is more reminiscent of the situation seen with low-temperature superconductors, those that work only at close to absolute zero. Theory says that electrons interacting with phonons pair up and travel through the superconductor easily without bouncing off atoms. Davis’ work suggests that, in part at least, something similar happens in high-temperature superconductivity too.
A topographic map of cuprate superconductor (Credit: Davis Lab/Cornell University)
We have shown that you can’t ignore the electron-phonon interaction, Davis explains. We can’t prove that it’s involved in the pairing, but we have proven that you can’t ignore it.
Further reading
J. C. Séamus Davis
http://www.physics.cornell.edu/people/faculty/?page=website/faculty&action=show/id=9
Suggested searches
superconductors
high temperature superconductors
scanning tunnelling microscopy