Emergence of preformed Cooper pairs from the doped Mott insulating state in Bi 2 Sr 2 CaCu 2 O 8+ δ

High-temperature superconductivity: primed for the pseudogap In conventional superconductors, the superconductivity is generated by pairs of electrons, called Cooper pairs. The energy needed to break these pairs is observable spectroscopically as an 'energy gap'. The high-transition temperature copper oxides have an additional 'pseudogap', detected at temperatures well above those associated with superconductivity. The origin of this pseudogap may provide clues as to the mechanism of high-temperature superconductivity. It has been unclear whether this represents preformed pairs of electrons that have not achieved the coherence necessary for superconductivity. Yang et al . now report a photoemission study of the underdoped copper oxide Bi 2 Sr 2 CaCu 2 O 8+ δ that reveals preformed pairs in the pseudogap, although the pairing occurs only in the anti-nodal region.