Brookhaven physicists have found ways to sharpen images of the energy spectra in high-temperature superconductors to reveal previously unobserved details about electron pairing. These new imaging methods confirm that the electron pairs needed to carry current emerge above the transition temperature, before superconductivity sets in.
The findings rule out certain explanations for the development of superconductivity in these materials, and lend support to other, competing theories. Honing in on the mechanism for high-temperature (high-Tc) superconductivity may help scientists engineer new materials to make use of the current-carrying phenomenon in transformative applications such as high-efficiency transmission lines in the U.S. power grid.
To search for pre-formed electron pairs, the Brookhaven team bombarded a copper-oxide material, held at temperatures above and below its transition temperature, with beams of light from the National Synchrotron Light Source, and analyzed the energy spectrum of electrons emitted from the sample. This technique allowed the scientists to look for symmetry in a so-called pseudogap they’d previously observed in the energy spectrum of some high-Tc materials well above the transition temperature. Symmetry in this gap would be a clear indication of electron pairing above the transition temperature. The Brookhaven team demonstrated that the pseudogap does indeed exhibit this symmetry, indicating that electrons are forming pairs before the material becomes a superconductor.
H.-B. Yang, J. D. Rameau, P. D. Johnson, T. Valla, A. Tsvelik, G. D. Gu, “Emergence of preformed Cooper pairs from the doped Mott insulating state in Bi2Sr2CaCu2O8+É¬,” Nature 456, 77 - 80 (06 Nov 2008)
Last Modified: November 04, 2009