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Abstract:
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
Fe1+delta 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 Fe1+delta 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 considered as intrinsic characteristics of
iron-based superconducting systems.
