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August 02, 2006

STM advance reveals high temp superconductor surprises

New atomic scale imaging reveals surprises about high temperature superconductors



Scanning tunneling microscope "topographic map" of a sample of cuprate semiconductor shows the locations of atoms in the crystal lattice. The inset shows how the current flow at a single point of the scan varies with voltage, with "kinks" (arrows) that indicate the presence of lattice vibrations and electron pairs.

Researchers found that the distribution of paired electrons in a common high-temperature superconductor was "disorderly," but that the distribution of phonons -- vibrating atoms in the crystal lattice -- was disorderly in just the same way. The theory of low-temperature superconductivity says that electrons interacting with phonons join into pairs that are able to travel through the conductor without being scattered by atoms. These results suggest that a similar mechanism may be at least partly responsible for high-temperature superconductivity.

They have shown that you can't ignore the electron-phonon interaction. They have not proved that it's involved in the pairing, but they have proven that you can't ignore it.

They advanced the use of scanning tunneling microscopes. Drawing on a 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 tunneling microscope (STM). The STM uses a probe so small that its tip is a single atom; positioned a few nanometers above the surface of a sample and moved in increments smaller than the diameter of an atom, it can scan a surface while current flowing between the tip and the surface is measured.

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