Foundation grantees at Cornell University have produced the first direct evidence of "Cooper pairs"-- coupled electrons that can carry electricity with zero resistance, or behave as a wave whose density varies across space.
In the 1950s, physicist Leon Cooper discovered electrons in a metal reduce their overall energy by pairing up. This behavior is responsible for superconductivity, which allows electrical current to flow inside a material with zero resistance, while expelling magnetic fields to its surface. This unique set of properties is used in technologies such as power transmission lines, MRI devices and Maglev trains.
In 1957, based on their findings, John Bardeen, Cooper and John Schrieffer developed the theory of superconductivity (usually called the BCS theory), which was later recognized with a Nobel Prize in physics.
The wave aspect of Cooper pairs has been impossible to pin down since it was first predicted because no microscope or other instrument was capable of observing Cooper pair density waves directly.
Now, EPiQS investigator and physicist J.C. Séamus Davis and colleagues at Max-Planck Institute CPMS in Dresden, Germany have unveiled direct evidence of a Cooper pair density wave state in a high-temperature superconductor.
The team used a scanning tunneling microscope to scan the surface of a high-temperature superconductor. By briefly lowering the tip of the microscope probe to touch the surface and pick up a flake of the superconducting material, Cooper pairs could then tunnel between the superconductor surface and the tip.
Current flow between the sample and the tip revealed the density of Cooper pairs at any point, showing periodic variations across the sample.
This work was recently published in Nature; read a Cornell article about the team's findings here.
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