NMR relaxation rate in superconducting pnictides: extended $s_{\pm}$ scenario

TL;DR

This paper demonstrates that the observed NMR relaxation rates in Fe-pnictide superconductors can be explained by an extended s±-wave symmetry of the order parameter, accounting for both the absence of a coherence peak and low-temperature power law behavior.

Contribution

It shows that the experimental NMR data are compatible with a nodeless extended s±-wave superconducting gap, challenging the interpretation of nodes based solely on power law behavior.

Findings

No coherence peak in $T_1^{-1}$ is consistent with s±-wave symmetry.

Low temperature power law behavior can be explained within the same model.

The results hold in both clean and dirty limits, with considerations beyond the Born approximation.

Abstract

Recently, several measurements of the nuclear spin lattice relaxation rate $T_{1}^{-1}$ in the newly discovered superconducting Fe-pnictides have been reported. These measurements generally show no coherence peak below $T_{c}$ and indicate a low temperature power law behavior, the characteristics commonly taken as evidence of unconventional superconductivity with lines of nodes crossing the Fermi surface. In this work we show that (i) the lack of a coherence peak is fully consistent with the previously proposed nodeless extended $s_{\pm}$-wave symmetry of the order parameter (whether in the clean or dirty limit) and (ii) the low temperature power law behavior can be also explained in the framework of the same model, but requires going beyond the Born model.