Cuprates, another high-temperature superconductor that layers copper and oxygen atoms, are natural insulators because of their oxygen layers. They must be doped to make them conductors.
Pnictides, on the other hand, are a metallic conductor. Despite their differences, however, both are high-temperature superconductors characterized by magnetic spins that are antiferromagnetic, that is, adjacent atoms have opposite spins. Below a critical temperature, quantum magnetic fluctuations change phases, thereby helping to explain superconduction.
"Our theory explains how electron-to-electron interactions can give rise to quantum magnetic fluctuations as the origin of superconductivity," Si claimed.
For superconductivity to occur, pairs of electrons must careen through metals in synchronized motion. Electrons also must overcome their natural repulsion for each other to couple in this way. In low-temperature superconductors, the Bardeen, Cooper, and Schrieffer (BCS) theory of superconductivity postulates that ionic vibrations in the lattice helps electrons pair up so they can slip through without bumping into its atoms. For high-temperature superconductors, however, the new theory postulates that magnetic interactions related to quantum criticality are responsible for superconductivity.
So far, the research is theoretical, but the scientisits have developed a set of specific predictions about how high-temperature superconductors behave as they change phases internally. These predictions are currently being tested by experimental groups around the world.
If the research holds up under laboratory scrutiny, then the new theory could take its place beside the BCS theory as the best explanation for high-temperature superconductors. That, in turn, could prompt a search for new materials with similar quantum phases in hopes of further raising the temperature of superconduction, ideally to room temperature.
Research funding was provided by the National Science Foundation, the Energy Department, the Robert A. Welch Foundation, the National Natural Science Foundation of China and the Education Ministry of China.