Extreme sensitivity of superconductivity to stoichiometry in Fe 1 + δ Se

The recently discovered iron arsenide superconductors appear to display a universal set of characteristic features, including proximity to a magnetically ordered state and robustness of the superconductivity in the presence of disorder. Here we show that superconductivity in ${\text{Fe}}_{1+\ensuremath{\delta}}\text{Se}$, which can be considered the parent compound of the superconducting arsenide family, is destroyed by very small changes in stoichiometry. Further, we show that nonsuperconducting ${\text{Fe}}_{1+\ensuremath{\delta}}\text{Se}$ is not magnetically ordered down to 5 K. These results suggest that robust superconductivity and immediate instability against an ordered magnetic state should not be…

• NS
  National Science Foundation

  Awards: 0819860, DMR-0819860
• UD
  U.S. Department of Energy

  Awards: DE-FG02-98ER45706, DE-FG02-, FG02-98ER45706, DE-FG02
• MR
  Materials Research Science and Engineering Center, Harvard University

  Award: DMR-0819860
• DO
  Division of Materials Research

  Award: DMR-0819860
• BE
  Basic Energy Sciences

  Awards: DE-FG02, DE-FG02-98ER45706