Ultrafast Melting of Superconductivity in an Iron-Based Superconductor

Intense debate has recently arisen regarding the photoinduced changes to the iron-chalcogenide superconductors, including the enhancement of superconductivity and a metastable state. Here, by employing high-energy resolution, we directly observe the melting of superconductivity on ultrafast timescales. We demonstrate a distinctly nonequilibrium response on short timescales, where the gap fills in prior to the destruction of the superconducting peak, followed by a metastable response. We propose that the former is due to pair phase decoherence and speculate that the latter is due to the increase in double-stripe correlations that are known to compete with superconductivity. Our results add to exciting new developments on the iron-based superconductors, indicating that the photoinduced metastable state possibly competes with superconductivity.