When it comes to superconductivity, magnetic excitations may top good vibrations. Scientists working at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) in collaboration with physicists from the University of Tennessee (UT) and Oak Ridge National Laboratory (ORNL) have discovered strong evidence that magnetic fluctuations are key to a universal mechanism for pairing electrons and enabling resistance-free passage of electric current in high-temperature superconductors. Their work is described in the July 6 issue of Nature.*
Phonons—vibrations in the atomic latticework—are responsible for the pairing-up of electrons in conventional, low-temperature, superconductors that allows for the characteristic, resistance-free flow of electrons. High-temperature superconductors, which have been objects of intense interest since their discovery in 1986, need some other pairing mechanism—phonons have been ruled out.
There are two main classes of high-temperature superconductors, those which have a surplus of electrons and those that have a surplus of electron vacancies or "holes." Previous work by other researchers has shown that magnetism plays a role in the superconductivity of the latter materials, but the mechanism for the former remained elusive. This work, using neutron probes at NCNR and ORNL's High Flux Isotope Reactor, forges a key link by demonstrating a magnetic resonance in an electron-doped, high-temperature superconductor.
The finding should boost efforts to develop a variety of useful technologies now considered impractical for conventional superconductors. Examples include loss-free systems for storing and distributing electric energy, superconducting digital routers for high-speed communications, and more efficient generators and motors.
NIST, the National Science Foundation and the Department of Energy supported the research.
For more information, see Researchers Peg Magnetism as Key Driver of High-Temperature Superconductivity.
*S.D. Wilson, P. Dai, S. Li, S. Chi, H.J. Kang, J.W. Lynn. 2006. Resonance in the electron-doped high-transition-temperature superconductor Pr0.88LaCe0.12CuO4-δ Nature. July 6, 2006.