Science Daily November 5, 2021
What distinguishes a superconducting state from a normal state is a spontaneously broken symmetry corresponding to the long-range coherence of pairs of electrons, leading to zero resistivity and diamagnetism. An international team of researchers (Germany, Sweden, Japan, France) was investigating the superconducting metal Ba1-xKxFe2As2 from the class of iron pnictides when they discovered that four electrons instead of two were forming a bond. It was scrutinized for two years using seven different methods to confirm the result. All data were consistent with the same result. Thus, they concluded that the four-particle electron family in certain metals creates a completely new state of matter when cooled to ultra-low temperatures. They have confirmed the theoretical prediction that there could be an unusual state of matter in certain superconducting metals, in which four instead of two electrons play a role. The discovery of iron pnictides as a class of materials particularly suitable for superconductivity already triggered a worldwide research boom in physics and materials science starting in 2008…read more. TECHNICAL ARTICLE
Time-reversal symmetry breaking in a superconducting state. Credit: Nature Physics (2021)Â