Extreme Sensitivity of Superconductivity to Stoichiometry in FeSe (Fe1+dSe)

TL;DR

This study reveals that superconductivity in Fe1+dSe is extremely sensitive to stoichiometry variations, with non-superconducting samples lacking magnetic order, challenging assumptions about intrinsic properties of iron-based superconductors.

Contribution

It demonstrates the delicate dependence of superconductivity on stoichiometry in Fe1+dSe and questions the presumed link between magnetism and superconductivity in these materials.

Findings

Superconductivity in Fe1+dSe is destroyed by minor stoichiometric changes.

Non-superconducting Fe1+dSe does not exhibit magnetic order at low temperatures.

Superconductivity's robustness and magnetic instability are not intrinsic to iron-based superconductors.

Abstract

The recently discovered iron arsenide superconductors, which display superconducting transition temperatures as high as 55 K, appear to share a number of general features with high-Tc cuprates, including proximity to a magnetically ordered state and robustness of the superconductivity in the presence of disorder. Here we show that superconductivity in Fe1+dSe, the parent compound of the superconducting arsenide family, is destroyed by very small changes in stoichiometry. Further, we show that non-superconducting Fe1+dSe is not magnetically ordered down to low temperatures. 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, and that Fe1+dSe may present a unique opportunity for determining which materials characteristics are critical to the existence of superconductivity in high Tc iron arsenide superconductors and which are not.