The research team performed measurements on the compound-which becomes superconducting at around 18 Kelvin-that reveal a magnetically mediated pairing of electrons. Some physicists consider that same mechanism to be the underlying cause of superconductivity in high-critical-temperature copper oxide superconductors.

Similar physical effects have been observed in another class of superconductors: the "heavy fermion" compounds, including CeCoIn5, which has a very low critical temperature, of 2.3 K. One unanswered question facing theorists is how compounds with widely disparate critical temperatures can be governed by the same superconducting mechanism. The new plutonium-based system is encouraging since it has a transition temperature between the lows of the heavy fermion superconductors and the high critical temperature of copper oxide superconductors. The Los Alamos researchers are confident that other exotic superconductors will soon be found.

In conventional low-critical-temperature superconductors, such as lead and niobium, electrons form into pairs under the influence of mechanical vibrations in the metal called phonons. Once paired up at a low enough temperature, the pairs merge into a single quantum state that represents a macroscopic quantum particle. One result is the flow of electrons through the metal with zero resistance.

In the type of superconductivity being discovered by the Los Alamos team, anti-ferromagnetic interchanges, rather than phonons, are the mechanism for formation of the electron pairs. While the same condensation into a single macroscopic quantum state occurs, the electron pairs have a net angular momentum that distinguishes them from the phonon-mediated pairs. The angular momentum produces different behavior, which can be detected experimentally.

One type of behavior generated by the net angular momentum is a strong directional component in the superconductivity-a behavior characteristic of the high-critical-temperature superconductors. The energy gap between the superconducting pairs and the remaining unpaired electrons drops to zero at regular intervals, forming excitation centers that can be observed.

Nicholas Curro led the Los Alamos team. Yunkyu Bang, a scientist at the Chonnam National University (South Korea), contributed to the work.