Effect of inelastic scattering on the nuclear magnetic relaxation rate 1/T1T in iron-based superconductors

TL;DR

This study investigates how inelastic scattering affects the nuclear magnetic relaxation rate in iron-based superconductors, revealing suppression of the coherence peak in optimally doped samples and potential emergence in heavily overdoped samples, with implications for pairing symmetry identification.

Contribution

The paper provides a microscopic evaluation of inelastic scattering effects on 1/T1 in iron-based superconductors, linking damping rates to doping levels and coherence peak behavior.

Findings

Coherence peak suppressed in optimally doped compounds due to large damping.

In heavily overdoped compounds, the coherence peak can reappear as damping decreases.

Discrimination between s++ and s+- pairing states remains challenging based on current data.

Abstract

We present a microscopic study of the nuclear magnetic relaxation rate 1/T1 based on the five-orbital model for iron-based superconductors. We mainly discuss the effect of the "inelastic" quasi-particle damping rate {\gamma} due to many-body interaction on the size of the coherence peak, for both s++ and s+- wave superconducting states. We focus on Ba(Fe1-xCox)2As2, and systematically evaluate {\gamma} in the normal state from the experimental resistivity, from optimally to over-doped compounds. Next, {\gamma} in the superconducting state is calculated microscopically based on the second order perturbation theory. In optimally doped compounds (Tc ~ 30 K), it is revealed that the coherence peak on 1/T1T is completely suppressed due to large {\gamma} for both s++ and s+- wave states. On the other hand, in heavily over doped compounds with Tc < 10 K, the coherence peak could appear for both pairing states, since {\gamma} at Tc is quickly suppressed in proportion to Tc^2. By making careful comparison between theoretical and experimental results, we conclude that it is difficult to discriminate between s++ and s+- wave states from the present experimental results.