Unconventional pairing in the iron arsenide superconductors

TL;DR

This paper demonstrates that iron arsenide superconductors exhibit unconventional, sign-changing pairing symmetry, supported by theoretical analysis and neutron diffraction experiments showing coexistence of antiferromagnetism and superconductivity.

Contribution

The study provides theoretical and experimental evidence that iron arsenide superconductors have an unconventional pairing mechanism with sign-changing Cooper pairs.

Findings

Coexistence of antiferromagnetism and superconductivity observed in Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$

Theoretical model predicts coexistence only with unconventional pairing

Experimental data matches the model, confirming unconventional pairing in these materials

Abstract

We use magnetic long range order as a tool to probe the Cooper pair wave function in the iron arsenide superconductors. We show theoretically that antiferromagnetism and superconductivity can coexist in these materials only if Cooper pairs form an unconventional, sign-changing state. The observation of coexistence in Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ then demonstrates unconventional pairing in this material. The detailed agreement between theory and neutron diffraction experiments, in particular for the unusual behavior of the magnetic order below $T_{c}$, demonstrates the robustness of our conclusions. Our findings strongly suggest that superconductivity is unconventional in all members of the iron arsenide family.