Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory, Cornell University, and collaborators have produced the first direct evidence of a state of electronic matter first predicted by theorists in 1964. The discovery, described in a paper published online April 13, 2016, in Nature, may provide key insights into the workings of high-temperature superconductors.
The prediction was that “Cooper pairs” of electrons in a superconductor could exist in two possible states. They could form a “superfluid” where all the particles are in the same quantum state and all move as a single entity, carrying current with zero resistance — what we usually call a superconductor. Or the Cooper pairs could periodically vary in density across space, a so-called “Cooper pair density wave.” For decades, this novel state has been elusive, possibly because no instrument capable of observing it existed.
Now a research team led by J.C. Séamus Davis, a physicist at Brookhaven Lab and the James Gilbert White Distinguished Professor in the Physical Sciences at Cornell, and Andrew P. Mackenzie, Director of the Max-Planck Institute CPMS in Dresden, Germany, has developed a new way to use a scanning tunneling microscope (STM) to image Cooper pairs directly.