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Sign Flips and Spin Fluctuations in Iron High-Tc Superconductors

The symmetry of electron-pairing interactions in iron-based superconductors suggests a shared spin-mediated pairing mechanism with the cuprate family. In superconductors, the key process that allows current to travel without resistance is the formation of electron pairs that move as a single quantum state. The mechanism of pairing in the high-temperature (high-Tc) cuprate superconductors is still elusive, so the recent discovery of iron-based superconductors (1) sparked the hope that comparison with the cuprates would lead to a better understanding of pairing in both materials. On page 474 of this issue, Hanaguri et al. (2) report the experimental determination of the pairing symmetry in FeSexTe1−x. Combined with the recent observation of a spin fluctuation resonance in this material (3) akin to that seen in the cuprates (4), a compelling hypothesis emerges that these high-Tc superconductors share a common pairing mechanism.