A complete theory explaining the physics of superconductors has yet to be developed. But German and US scientists are taking steps towards understanding the mechanisms that could lead to one.

Researchers from the Max Planck Institute of Solid State Research in Munich have found what they believe to be an explan-ation of the mechanism behind high-temperature superconductivity, and a team from Berkley in Cali-fornia have raised questions about some fundamental superconductor theories.

Professor Bernhard Keimer, a director at the Max Planck Institute, said: "Our discovery contributes to the understanding of high-temperature superconductivity."

The Max Planck team investigated the 'mosaic' of crystals of a high-temperature superconductor using neutron beams. They built several hundred small crystals in a mosaic which, as a whole, behaved like a large single crystal. This made neutron scattering experiments possible

Using a neutron beam, the team discovered a fluctuating magnetic order in high-temperature superconductors; the electrons' spin orientation formed an ordered structure.

The spin of every second electron is opposite that of the first, with the two forming Cooper pairs. The idea of Cooper pairs emerged from work by Einstein and Satyendra Nath Bose in the 1920s.

They showed that in a metal below a transition temperature, two free electrons form a 'Cooper pair', effectively forming a single particle — a boson. At low enough temperatures, the bosons condense into a coherent state in which the bosons move through the material without any resistance.

The Max Planck work suggests that something similar is happening in high-temperature superconductors. The neutron scattering experiments suggest the electron spin order fluctuates, appearing and disappearing.

Prof Keimer said: "The origin of the pairing force may be that pairs of electrons can move more easily than single free electrons through a background of fluctuating electron spins — they could thus save magnetic energy. Our results may put a definite theory of high-temperature superconductivity finally within reach."

The Berkley team has identified a 'kink' in the energy spectrum of low-energy electrons in three families of copper oxide high-temperature superconductors.

Zhi-Xun Shen, Stanford University physicist and project leader, said, "We discovered that the electrons' motion in these superconductors are strongly influenced by the lattice vibration. This may have important implications on why these materials superconduct."

This kink in the spectrum would seem to indicate interaction or 'coupling' between an electron and a phonon, a vibration in the ions that form the lattice of a superconductor's crystal.

"This discovery will give more insight on why high-Tc superconductivity occurs which, in the long run, may influence the way we develop superconductors," he said.

Superconductors have been used in, or proposed for use in base stations, memory chips, alternative energy storage systems and magnetic levitation trains.